HR (Hertzsprung-Russell) Diagram Solution#

The Hertzsprung-Russell diagram is a fundamental diagram in astronomy that displays important relationships between the stellar color (or temperature) and absolute brightness (or luminosity).

In this exercise, we will use existing stellar catalogs to produce the H-R diagram.

# As a hint, we include the code block for Python modules that you will likely need to import:
import matplotlib
import matplotlib.pyplot as plt
import numpy as np
%matplotlib inline

# For downloading files
from astropy.utils.data import download_file
from astropy.io import fits

import pyvo as vo
from pyvo import registry

## There are a number of relatively unimportant warnings that
## show up, so for now, suppress them:
import warnings
warnings.filterwarnings("ignore", module="astropy.io.votable.*")
warnings.filterwarnings("ignore", module="pyvo.utils.xml.*")

Step 1: Find appropriate catalogs#

We want to find a star catalog that has the available data to produce the H-R diagram, i.e., the absolute magnitudes (or both apparent magnitudes AND distances, so we can calculate the absolute magnitudes) in two optical bands (e.g., B and V). This would give us color. Or we need B- OR V- band magnitude and the stellar temperature.

To simplify this problem, we want to find a catalog of an open cluster of stars, where all the stars were born around the same time and are located in one cluster. This simplifies the issue of getting accurate distances to the stars. One famous cluster is the Pleiades in the constellation of Taurus. So first we start by searching for an existing catalog with data on Pleiades that will provide the necessary information about the stars: magnitudes in two bands (e.g., B and V), which can be used to measure color, or temperature of the star plus one magnitude.

DATA DISCOVERY STEPS#

Here is useful link for how the pyvo registry search works.

tap_services = registry.search(servicetype = 'tap', keywords=['star pleiades'], includeaux=True)
print(len(tap_services))
tap_services.get_summary()

Table length=137

index	short_name	title	description	interfaces
int64	str16	str55	str4800	str7
0	I/163	US Naval Observatory Pleiades Catalog	This catalog is a special subset of the Eichhorn et al. (1970) Pleiades catalog (see <I/90>) updated to B1950.0 positions and with proper motions added. It was prepared for the purpose of predicting occultations of Pleiades stars by the Moon, but is useful for general applications because it contains many faint stars not present in the current series of large astrometric catalogs.	tap#aux
1	I/258	Pleiades positions and proper motions	Based on a preliminary reference catalogue, combined with the catalogues PPM, ACRS and those in Eichhorn et al (1970, Cat. <I/90>), Jones (1973A&AS....9..313J) and Hertzsprung (1947AnLei..19a...1H), 33 exposures on 11 plates taken with the Zo-Se 40cm refractor (f=6895mm) in 86 years are reduced with the central overlapping technique, and high-precision positions and proper motions of 441 stars in the Pleiades astrometric standard region are obtained. The standard errors of star positions are less than +/-0.05arcsec, and the standard errors of proper motions for 90% stars in our reduction are less than +/-0.001arcsec/yr.	tap#aux
2	I/90	Positions of 502 Stars in Pleiades Region	The catalog contains the positions (equinox B1900.0 and epoch B1955.0) of 502 stars in a region of about 1.5 degrees square in the Pleiades cluster, centered on Eta Tau. These coordinates have been derived from measurements of stellar images obtained with 65 exposures of various durations on 14 photographic plates with two telescopes at McCormick Observatory and Van Vleck Observatory. The plates were reduced by the plate overlap method, which resulted in a high degree of systematic accuracy in the final positions. Data in the machine version include Hertzsprung number, color index, photovisual magnitude, right ascension and declination and their standard errors, proper motion, and differences between the present position and previous works. Data for exposures, plates, and images measured, present in the published catalog, are not included in the machine version.	tap#aux
3	II/131	Tonantzintla Pleiades Flare Stars	The original catalog lists the flare stars discovered by different astronomical observatories over an area slightly larger than 20 square degrees in the Pleiades regions centered on Alcyone. Not all the flare stars are members of this cluster, membership indicators are provided in the catalog. The catalog, combining Tables 1 and 2 of the publication, gives the data for 1531 flares of 519 flare stars.	tap#aux
4	II/44	K-Line photometry of stars in Population I clusters	Photoelectric photometry of the K-line of calcium has been performed for the A stars of five open clusters (Hyades, Pleiades, IC 2391, IC 2602, and NGC 6475) and one association (Orion). All observations were carried out simultaneously with the field stars measurements in Paper II (II/43), with the 16-inch (40cm) and 36-inch (91cm) telescopes of the Cerro Tololo Inter-American Observatory, between May 1969 and January 1970.	tap#aux
5	J/A+A/299/696	Pleiades field Membership probabilities	A catalogue of proper motions and photographic B,V magnitudes for stars up to B=19 mag within a region centered near Alcyone is presented. The catalogue is based on MAMA measurements of 8 plates taken with the Tautenburg Schmidt telescope. The survey includes ca. 14500 stars and covers a total field of about 9 square degrees. Membership probabilities, proper motions and B,V magnitudes are listed for 442 stars up to B=19 mag in the Pleiades field.	tap#aux
6	J/A+A/320/74	Radial velocities of Pleiades members	The analysis of CORAVEL radial velocities of 93 stars selected on the basis of their proper motion and Geneva CCD photometric observations for 57 stars have permitted to identify 25 new members in the outer part of the Pleiades. Several spectroscopic binaries have been discovered, but their membership is not clear. Two orbits with short periods have been determined, but both stars are probably non-members. The total number of member stars in the outer part of the Pleiades in the spectral range F5-K0 (0.45<B-V<0.90) is now 81 which is comparable to the number of stars known in Hertzsprung's central area (88 stars) in the same spectral domain. Therefore at least 48% of the F5-K0 main-sequence stars are located in the outer part of the cluster. And the census is probably still incomplete.	tap#aux
7	J/A+A/323/139	K magnitude of Pleiades low-mass binaries	This table provides the list of stars observed but not resolved during the diffraction-limited survey of G and K Pleiades dwarfs. Previously known binaries, either photometric or spectroscopic, are referenced.	tap#aux
8	J/A+A/325/647	High-resolution spectra south of Taurus	Listed are results from our high-resolution data for all stars in our study area which were listed by either Magazzu et al. (1997A&AS..124..449M) or Alcala et al. (1996A&AS..119....7A), i.e. T Tauri candidates from the ROSAT All-Sky Survey. In table 1, we list all stars for which lithium was found either by Magazzu et al. (1997A&AS..124..449M) or in our CASPEC spectra, as well as two stars identified as wTTS by Alcala et al. (1996A&AS..119....7A). Listed are the designation, number of single-order echelle spectra taken, effective temperatures, projected rotational velocities, mean heliocentric radial velocities with errors, radial velocities in the local standard of rest, and remarks on variability in radial velocity as found in our high-resolution spectra. For comparison, we also list the results on spectral types of the stars (with `e' for H{alpha} emission) as found by Magazzu et al. (1997A&AS..124..449M) (or Alcala et al., 1996A&AS..119....7A) with low- and medium-resolution spectroscopy. In the last two columns, we list the (NLTE) lithium abundance (given on a scale where logN(H)=12) and the lithium excess above the relevant Pleiades upper envelope; upper limits indicate stars where the Magazzu et al. (1997A&AS..124..449M) spectra suffer from either low S/N or low resolution. In table 2, we list all stars where no lithium was detected -- neither by Magazzu et al. (1997A&AS..124..449M) nor in our CASPEC spectra.	tap#aux
9	J/A+A/329/101	Masses of Pleiades members	On the basis of the best available member list and duplicity information, we have studied the radial distribution of 270 stars and multiple systems earlier than K0 in the Pleiades. Five new long period spectroscopic binaries have been identified from the CORAVEL observations. We have found a clear mass segregation between binaries and single stars, which is explained by the greater average mass of the multiple systems. The mass function of the single stars and primaries appears to be significantly different. While the central part of the cluster is spherical, the outer part is clearly elliptical, with an ellipticity of 0.17. The various parameters describing the Pleiades are (for a distance of 125pc): core radius r_c_=0.6 deg (1.4pc), tidal radius r_t_=7.4 (16pc), half mass radius r_m/2_=0.88 (1.9pc), harmonic radius r=1.82 (4pc). Low-mass stars (later than K0) probably extend further out and new proper motion and radial velocity surveys over a larger area and to fainter magnitudes would be very important to improve the description of the cluster structure and complete mass function.	tap#aux
...	...	...	...	...
127	2MASS 6XMPSIT	2MASS 6X Merged Point Source Information Table	During the final months of 2MASS observatory operations, a campaign of targeted "long exposure" observations was carried out during times when no previously unscanned parts of the sky were available for the main survey. These observations used the same freeze-frame scanning technique employed for the survey, but with READ2-READ1 exposures six times longer than was used for normal survey observations (hence they are referred to as "6x" observations). The 2MASS 6x measurements were intended to probe ~1 magnitude deeper than the main survey in unconfused regions.\n\nApproximately 590 deg2 of sky distributed in 30 targeted regions were scanned at least once using the long exposures. Most of this area is concentrated in two large, comprehensive surveys of the Large and Small Magellanic Clouds, 383 deg2 and 127 deg2, respectively. Twenty-eight additional smaller fields were mapped in the 6x mode from both observatories, covering targets that include the Pleiades open cluster, galactic star formation complexes, M31, nearby galaxy clusters and the Lockman Hole. \n\nThe merged source tables contain the mean positions magnitudes and uncertainties for sources detected multiple times in each of the 2MASS data sets. The merging was carried out using an autocorrelation of the respective databases to identify groups of extractions that are positionally associated with each other, all lying within a 1.5" radius circular region. A number of confirmation statistics are also provided in the tables that can be used to test for source motion and/or variability, and the general quality of the merge.	tap#aux
128	2MASS 6XMXSIT	2MASS 6X Merged Extended Source Information Table	During the final months of 2MASS observatory operations, a campaign of targeted "long exposure" observations was carried out during times when no previously unscanned parts of the sky were available for the main survey. These observations used the same freeze-frame scanning technique employed for the survey, but with READ2-READ1 exposures six times longer than was used for normal survey observations (hence they are referred to as "6x" observations). The 2MASS 6x measurements were intended to probe ~1 magnitude deeper than the main survey in unconfused regions.\n\nApproximately 590 deg2 of sky distributed in 30 targeted regions were scanned at least once using the long exposures. Most of this area is concentrated in two large, comprehensive surveys of the Large and Small Magellanic Clouds, 383 deg2 and 127 deg2, respectively. Twenty-eight additional smaller fields were mapped in the 6x mode from both observatories, covering targets that include the Pleiades open cluster, galactic star formation complexes, M31, nearby galaxy clusters and the Lockman Hole. \n\nThe merged source tables contain the mean positions magnitudes and uncertainties for sources detected multiple times in each of the 2MASS data sets. The merging was carried out using an autocorrelation of the respective databases to identify groups of extractions that are positionally associated with each other, all lying within a 1.5" radius circular region. A number of confirmation statistics are also provided in the tables that can be used to test for source motion and/or variability, and the general quality of the merge.	tap#aux
129	2MASS 6XPSWDB	2MASS 6X Point Source Working Database Table	During the final months of 2MASS observatory operations, a campaign of targeted "long exposure" observations was carried out during times when no previously unscanned parts of the sky were available for the main survey. These observations used the same freeze-frame scanning technique employed for the survey, but with READ2-READ1 exposures six times longer than was used for normal survey observations (hence they are referred to as "6x" observations). The 2MASS 6x measurements were intended to probe ~1 magnitude deeper than the main survey in unconfused regions.\n\nApproximately 590 deg2 of sky distributed in 30 targeted regions were scanned at least once using the long exposures. Most of this area is concentrated in two large, comprehensive surveys of the Large and Small Magellanic Clouds, 383 deg2 and 127 deg2, respectively. Twenty-eight additional smaller fields were mapped in the 6x mode from both observatories, covering targets that include the Pleiades open cluster, galactic star formation complexes, M31, nearby galaxy clusters and the Lockman Hole. \n\nData processing produced a 6x Image Atlas and 6x point and extended source Working Databases (6x-PSWDB and 6x-XSWDB), analogous to those from the main survey. "Catalogs" of point and extended source detections (6x-PSC and 6x-XSC) that represent uniform, higher reliability single-epoch snapshots of the near infrared sky were drawn from the 6x WDBs using SNR and quality criteria similar to those used to construct the All-Sky Release PSC and XSC (A3.6.c). The 6x-PSC and 6x-XSC have not received the same level of scrutiny and validation as the 2MASS All-Sky PSC and XSC, though.\n\nUnlike the All-Sky Release Catalogs, the 6x Catalogs are not released as separate tables. The 6x Point and Extended Source Catalogs are instead integrated into the respective 6x Point and Extended Source WDBs. Sources comprising the Catalogs are denoted in the WDBs with the cat flag, and have cat="1".	tap#aux
130	2MASS 6XScanInfo	2MASS 6X Scan Information Table	During the final months of 2MASS observatory operations, a campaign of targeted "long exposure" observations was carried out during times when no previously unscanned parts of the sky were available for the main survey. These observations used the same freeze-frame scanning technique employed for the survey, but with READ2-READ1 exposures six times longer than was used for normal survey observations (hence they are referred to as "6x" observations). The 2MASS 6x measurements were intended to probe ~1 magnitude deeper than the main survey in unconfused regions.\n\nApproximately 590 deg2 of sky distributed in 30 targeted regions were scanned at least once using the long exposures. Most of this area is concentrated in two large, comprehensive surveys of the Large and Small Magellanic Clouds, 383 deg2 and 127 deg2, respectively. Twenty-eight additional smaller fields were mapped in the 6x mode from both observatories, covering targets that include the Pleiades open cluster, galactic star formation complexes, M31, nearby galaxy clusters and the Lockman Hole. \n\nThe 6X Scan Information Table provides basic metadata for each survey mode scan taken during 2MASS 6x observations.	tap#aux
131	2MASS 6XXSWDB	2MASS 6X Extended Source Working Database Table	During the final months of 2MASS observatory operations, a campaign of targeted "long exposure" observations was carried out during times when no previously unscanned parts of the sky were available for the main survey. These observations used the same freeze-frame scanning technique employed for the survey, but with READ2-READ1 exposures six times longer than was used for normal survey observations (hence they are referred to as "6x" observations). The 2MASS 6x measurements were intended to probe ~1 magnitude deeper than the main survey in unconfused regions.\n\nApproximately 590 deg2 of sky distributed in 30 targeted regions were scanned at least once using the long exposures. Most of this area is concentrated in two large, comprehensive surveys of the Large and Small Magellanic Clouds, 383 deg2 and 127 deg2, respectively. Twenty-eight additional smaller fields were mapped in the 6x mode from both observatories, covering targets that include the Pleiades open cluster, galactic star formation complexes, M31, nearby galaxy clusters and the Lockman Hole. \n\nData processing produced a 6x Image Atlas and 6x point and extended source Working Databases (6x-PSWDB and 6x-XSWDB), analogous to those from the main survey. "Catalogs" of point and extended source detections (6x-PSC and 6x-XSC) that represent uniform, higher reliability single-epoch snapshots of the near infrared sky were drawn from the 6x WDBs using SNR and quality criteria similar to those used to construct the All-Sky Release PSC and XSC (A3.6.c). The 6x-PSC and 6x-XSC have not received the same level of scrutiny and validation as the 2MASS All-Sky PSC and XSC, though.\n\nUnlike the All-Sky Release Catalogs, the 6x Catalogs are not released as separate tables. The 6x Point and Extended Source Catalogs are instead integrated into the respective 6x Point and Extended Source WDBs. Sources comprising the Catalogs are denoted in the WDBs with the cat flag, and have cat="1".	tap#aux
132	NGC2516XMM	NGC 2516 Cluster XMM-Newton X-Ray Point Source Catalog	This table contains the results from a deep X-ray survey of the young (~ 140 Myr), rich open cluster NGC 2516 obtained with the EPIC camera on board the XMM-Newton satellite. By combining the data from six observations, a high sensitivity, greater than a factor of 5 with respect to recent Chandra observations, has been achieved. Kaplan-Meier estimators of the cumulative X-ray luminosity distribution, statistically corrected for non-member contaminants, were built by the authors and compared to those of the nearly coeval Pleiades cluster. 431 X-ray sources were detected, and 234 of them have as optical counterparts cluster stars spanning the entire NGC 2516 main sequence. On the basis of X-ray emission and optical photometry, 20 new candidate members of the cluster have been identified; at the same time there are 49 X-ray sources without known optical or infrared counterpart. The X-ray luminosities of cluster stars span the range log L<sub>x</sub> (erg s<sup>-1</sup>) = 28.4 - 30.8. The representative coronal temperatures span the 0.3 - 0.6 keV (3.5 - 8 MK) range for the cool component and 1.0 - 2.0 keV (12 - 23 MK) for the hot one; similar values were found in other young open clusters like the Pleiades, IC 2391, and Blanco 1. While no significant differences were found in their X-ray spectra, NGC 2516 solar-type stars are definitely less luminous in X-rays than their nearly coeval Pleiades counterparts. The comparison with a previous ROSAT survey reveals the lack of variability amplitudes larger than a factor of 2 in solar-type cluster stars in a ~ 11 yr time scale, and thus activity cycles like in the Sun are probably absent or have a different period and amplitude in young stars. NGC 2516 has been observed several times with XMM-Newton during the first two years of satellite operations for calibration purposes. The observations used in this analysis span a period of 19 months with exposure times between 10 and 20 ks. All of these observations have been performed with the thick filter. In the combined EPIC datasets the authors detected 431 X-ray sources with a significance level greater than 5.0 sigma, which should lead statistically to at most one spurious source in the field of view.	tap#aux
133	NGC2547XMM	NGC 2547 XMM-Newton X-Ray Point Source Catalog	This table contains a list of point sources detected by XMM-Newton EPIC in a pointing towards the young open cluster NGC 2547, made in order to allow the authors to characterize coronal activity in solar-type stars, and stars of lower mass, at an age of 30 Myr. X-ray emission was seen from stars at all spectral types, peaking among G stars at luminosities (0.3 - 3 keV) of L<sub>x</sub> ~= 10<sup>30.5</sup> erg/s and declining to L<sub>x</sub> <= 10<sup>29</sup> erg/s among M stars with masses >=0.2 solar masses. Coronal spectra show evidence for multi-temperature differential emission measures and low coronal metal abundances of Z~= 0.3. Most of the solar-type stars in NGC 2547 exhibit saturated or even supersaturated X-ray activity levels. The median levels of L<sub>x</sub> and L<sub>x</sub>/L<sub>bol</sub> in the solar-type stars of NGC 2547 are very similar to those in T-Tauri stars of the Orion Nebula cluster (ONC), but an order of magnitude higher than in the older Pleiades. The spread in X-ray activity levels among solar-type stars in NGC 2547 is much smaller than in older or younger clusters. This table contains the properties of those X-ray sources which are correlated with optical cluster members (see Section 2.2 of the reference paper for details on the correlation procedure that was adopted), as well as the properties of those X-ray sources which are uncorrelated with any optical cluster members. The table lists the cross-identifications with optical catalogs for the candidate cluster sources along with their X-ray luminosities and X-ray to bolometric flux ratios, as well as the correlations between cluster members which were detected by XMM-Newton and those detected 7 years earlier by the ROSAT HRI instrument, along with the X-ray luminosities and flux ratios as determined by the HRI.	tap#aux
134	NGC752CXO	NGC 752 Chandra X-Ray Point Source Catalog	This table provides a list of X-ray sources detected in a ~140 ks Chandra X-ray observation of the open cluster NGC 752. For the sources with 2MASS counterparts, the values of their magnitudes in the J, H and K bands are also given. Very little is known about the evolution of stellar activity between the ages of the Hyades (0.8 Gyr) and the Sun (4.6 Gyr). To gain information on the typical level of coronal activity at a star's intermediate age, the authors have studied the X-ray emission from stars in the 1.9 Gyr-old open cluster NGC 752. They analyzed a ~ 140 ks Chandra observation of NGC 752 and a ~50 ks XMM-Newton observation of the same cluster. They detected 262 X-ray sources in the Chandra data and 145 sources in the XMM-Newton observation. Around 90% of the catalogued cluster members within Chandrás field of view are detected in the X-ray observation. The X-ray luminosity of all observed cluster members (28 stars) and of 11 cluster member candidates was derived. These data indicate that, at an age of 1.9 Gyr, the typical X-ray luminosity L<sub>x</sub> of the cluster members with masses of 0.8 to 1.2 solar masses is 1.3 x 10<sup>28</sup> erg s<sup>-1</sup>, which is approximately a factor of 6 times less intense than that observed in the younger Hyades. Given that L<sub>x</sub> is proportional to the square of a star's rotational rate, the median L<sub>x</sub> of NGC 752 is consistent, for t >= 1 Gyr, with a decaying rate in rotational velocities v<sub>rot</sub> ~ t<sup>-alpha</sup> with alpha ~ 0.75, steeper than the Skumanich relation (alpha ~ 0.5) and significantly steeper than that observed between the Pleiades and the Hyades (where alpha <0.3), suggesting that a change in the rotational regimes of the stellar interiors is taking place at an age of ~ 1 Gyr. The 135 ks observation of NGC 752 was performed by the Chandra ACIS camera on September 29, 2003 starting at 21:11:59 UT. The X-ray source detection was performed on the event list using the Wavelet Transform detection algorithm developed at Palermo Astronomical Observatory PWDETECT, available at <a href="http://oapa.astropa.unipa.it/progetti_ricerca/PWDetect">http://oapa.astropa.unipa.it/progetti_ricerca/PWDetect</a>. Initially, the energy range 0.2 - 10 keV was selected and the threshold for source detection was taken as to ensure a maximum of 1-2 spurious sources per field. 169 sources were detected in this way. The analysis of these sources hardness ratios showed, however, that all the catalogued stars in the field had low hardness ratios, HR < ~ 0.2, where HR is the number of photons in the 2 - 8 keV band over the number in the 0.5 - 2 keV band. Thus, to maximize the detection of stellar sources, PWDETECT was applied to the event list in the energy range from 0.5 - 2 keV. Using a detection threshold which ensures less than 1 spurious source per field leads to the detection of 188 sources, while lowering this threshold to 10 spurious sources per field, allows 262 sources to be identified in this energy range. This is a significant increase (well above the number expected if all the additional sources were spurious), thus the authors retained this list of 262 sources as their final list of sources in the NGC 752 field, with the caveat that ~ 10 sources among them are likely spurious. Note that the existence of ~ 10 spurious sources in the list is not so much of a problem in this context, because cluster members or candidate members are identified by the existence of a visible or near-IR counterpart. The authors searched for 2MASS counterparts to the X-ray sources using the 2MASS Point Source Catalogue (PSC) and a search radius of 3 arcsec and found a counterpart for 43 sources. Searching within the Point Source Reject Table of the 2MASS Extended Mission leads to the further identification of 1 counterpart (source number 87).	tap#aux
135	NGC752XMM	NGC 752 XMM-Newton X-Ray Point Source Catalog	This table provides a list of X-ray sources detected in a ~50 ks XMM-Newton X-ray observation of the open cluster NGC 752. For the sources with 2MASS counterparts, the values of their magnitudes in the J, H and K bands are also given. Additionally, for the sources with a Chandra counterpart (within a search radius of 5 arcsec), the values of their Chandra source number (as given in the related Browse table NGC752CXO) are also given. Very little is known about the evolution of stellar activity between the ages of the Hyades (0.8 Gyr) and the Sun (4.6 Gyr). To gain information on the typical level of coronal activity at a star's intermediate age, the authors have studied the X-ray emission from stars in the 1.9 Gyr-old open cluster NGC 752. They analyzed a ~ 140 ks Chandra observation of NGC 752 and a ~50 ks XMM-Newton observation of the same cluster. They detected 262 X-ray sources in the Chandra data and 145 sources in the XMM-Newton observation. Around 90% of the catalogued cluster members within Chandrás field of view are detected in the X-ray observation. The X-ray luminosity of all observed cluster members (28 stars) and of 11 cluster member candidates was derived. These data indicate that, at an age of 1.9 Gyr, the typical X-ray luminosity L<sub>x</sub> of the cluster members with masses of 0.8 to 1.2 solar masses is 1.3 x 10<sup>28</sup> erg s<sup>-1</sup>, which is approximately a factor of 6 times less intense than that observed in the younger Hyades. Given that L<sub>x</sub> is proportional to the square of a star's rotational rate, the median L<sub>x</sub> of NGC 752 is consistent, for t >= 1 Gyr, with a decaying rate in rotational velocities v<sub>rot</sub> ~ t<sup>-alpha</sup> with alpha ~ 0.75, steeper than the Skumanich relation (alpha ~ 0.5) and significantly steeper than that observed between the Pleiades and the Hyades (where alpha <0.3), suggesting that a change in the rotational regimes of the stellar interiors is taking place at an age of ~ 1 Gyr. NGC 752 was observed for 49 ks by the XMM-Newton EPIC camera on February 5, 2003 starting at 23:29:25 UT, and the nominal pointing was towards J2000.0 RA and Declination of (01:57:38, +37:47:60), thus the XMM-Newton field-of-view (FOV) includes the Chandra FOV. For the source detection, the authors used the PWXDETECT code developed at Palermo Observatory and derived from the analogous Chandra PWDETECT code based on wavelet transform analysis. This allows the three EPIC exposures (PN, MOS1 and MOS2) to be combined in order to gain a deeper sensitivity with respect to the source detection based on single images. There were 145 point sources detected in the energy band 0.5 - 2.0 keV. An extended source (not listed in this present table), very likely a galaxy cluster, is also visible in the EPIC data. The authors searched for 2MASS counterparts to the XMM-Newton sources using a search radius of 5 arcsec and found a counterpart for 38 sources. As for the Chandra data, all sources with a visible counterpart from DLM94 have also a 2MASS counterpart, so this leaves 15 XMM-Newton sources with a 2MASS counterpart and no counterpart in Daniel et al. (1994, PASP, 106, 281); of these, 3 were also detected by Chandra; of the other 12, 10 are outside the Chandra FOV, while two are within it (XMM-Newton sources 58 and 65). Source 65 was caught by XMM-Newton during the decay phase of a flare, which explains why it is not detected in the Chandra data. For source 58 there is no immediate explanation for this, since the light curve does not show evidence of a flare. No additional near-IR counterpart to the XMM-Newton sources was found within the Point Source Reject Table of the 2MASS Extended Mission.	tap#aux
136	PSPC/Pleiades	ROSAT PSPC Catalog of the Pleiades (Micela et al. 1996)	This catalog contains the results of a deep X-ray survey of the core region of the Pleiades open cluster carried out with ROSAT. In a single PSPC field (~1 degree in radius), 99 of 214 Pleiades stars are detected in X-rays, and upper limits are computed for the remainder. This catalog lists the characteristics of these stars taken from the literature, including their rotational data, as well as their X-ray characteristics. The nucleus of the composite catalog used in this study is the catalog compiled from the published literature for the Einstein investigations of the Pleiades (Micela et al. 1990, ApJ, 348, 557). This list has been extended by the results of recent surveys to a completeness limit of visual magnitude of about 18.	tap#aux

Note: The includeaux=True includes auxiliary services.

Because we specified the service type, this returns only the TAP services for each of the avalible resorces matching our search criteria. So, the ‘interfaces’ column will only show TAP service as an avalible service, even if other services are avalible from the same resource. We know we need the service to be a TAP service since we know that we want to eventually access the search using additional column information (i.e., beyond RA and Dec, which is all that Simple Cone Search returns).

Next, we need to find which of these has the columns of interest, i.e. magnitudes in two bands to create the color-magnitude diagram#

We can re-run the registry search, but further restrict the results by column UCD. We want tables that have magnitude columns; the most basic UCD to describe a magnitude column is phot.mag

tap_services = registry.search(servicetype='tap', keywords=['star pleiades'],
                               ucd = ['phot.mag%'], includeaux=True)
print(len(tap_services))

Note: the ‘%’ serves as a wild card when searching by UCD

The IOVA standard enables resources to be as sepecific as they would like when defining the UCD of columns. For example, ‘phot.mag’ and ‘phot.mag;em.opt.V’ can both be used to describe a column containing the V magnitudes of objects. If a resource uses the latter to describe a column, a search using ‘phot.mag’ will not return that resource. A wild card would need to be used or the exact column UCD. The UCD search requires an exact match for a resource to be returned, so using the wild card will make it easier to discover a wider variety of resources.

So using this we can reduce the matched tables to ones that are a bit more catered to our experiment. Note, that there can be redundancy in some resources since these are available via multiple services and/or publishers. Therefore a bit more cleaning can be done to provide only the unique matches.

tap_services.to_table()['ivoid']

ivo://cds.vizier/i/163

ivo://cds.vizier/i/90

ivo://cds.vizier/ii/131

ivo://cds.vizier/ii/44

ivo://cds.vizier/j/a+a/299/696

ivo://cds.vizier/j/a+a/320/74

ivo://cds.vizier/j/a+a/323/139

ivo://cds.vizier/j/a+a/329/101

ivo://cds.vizier/j/a+a/332/575

ivo://cds.vizier/j/a+a/333/897

ivo://cds.vizier/j/a+a/341/751

ivo://cds.vizier/j/a+a/375/863

...

ivo://cds.vizier/j/mnras/476/3245

ivo://cds.vizier/j/mnras/483/1125

ivo://cds.vizier/j/mnras/492/1008

ivo://cds.vizier/j/other/rmxaa/53.439

ivo://cds.vizier/j/other/rmxaa/56.139

ivo://cds.vizier/j/pasj/68/92

ivo://cds.vizier/v/140

ivo://nasa.heasarc/ngc2516xmm

ivo://nasa.heasarc/ngc2547xmm

ivo://nasa.heasarc/ngc752cxo

ivo://nasa.heasarc/ngc752xmm

ivo://nasa.heasarc/pleiadxray

def getunique( result ):
    short_name = []
    unique_ind = []
    for i in range(len(result)):
        short = result[i].short_name
        if short not in short_name:
            short_name.append(short)
            unique_ind.append(i)
        else:
            print(i)

    return(unique_ind)

uniq_ind=getunique(tap_services)
print(len(uniq_ind))

tap_services.to_table()[uniq_ind]['ivoid']

ivo://cds.vizier/i/163

ivo://cds.vizier/i/90

ivo://cds.vizier/ii/131

ivo://cds.vizier/ii/44

ivo://cds.vizier/j/a+a/299/696

ivo://cds.vizier/j/a+a/320/74

ivo://cds.vizier/j/a+a/323/139

ivo://cds.vizier/j/a+a/329/101

ivo://cds.vizier/j/a+a/332/575

ivo://cds.vizier/j/a+a/333/897

ivo://cds.vizier/j/a+a/341/751

ivo://cds.vizier/j/a+a/375/863

...

ivo://cds.vizier/j/mnras/476/3245

ivo://cds.vizier/j/mnras/483/1125

ivo://cds.vizier/j/mnras/492/1008

ivo://cds.vizier/j/other/rmxaa/53.439

ivo://cds.vizier/j/other/rmxaa/56.139

ivo://cds.vizier/j/pasj/68/92

ivo://cds.vizier/v/140

ivo://nasa.heasarc/ngc2516xmm

ivo://nasa.heasarc/ngc2547xmm

ivo://nasa.heasarc/ngc752cxo

ivo://nasa.heasarc/ngc752xmm

ivo://nasa.heasarc/pleiadxray

This shows that in this case, all of our TAP results are unique.

We can read more information about the results we found. For each resource element (i.e. row in the table above), there are useful attributes, which are described here

# To read the descriptions of the resulting matches:

for i in uniq_ind:
    print("  ***  \n")
    print(tap_services[i].creators)
    print(tap_services[i].res_description)

  ***  

['Van Flandern T.C.']
This catalog is a special subset of the Eichhorn et al. (1970) Pleiades catalog (see <I/90>) updated to B1950.0 positions and with proper motions added. It was prepared for the purpose of predicting occultations of Pleiades stars by the Moon, but is useful for general applications because it contains many faint stars not present in the current series of large astrometric catalogs.
  ***  

['Eichhorn H.', ' Googe W.D.', ' Lukac C.F.', ' Murphy J.K.']
The catalog contains the positions (equinox B1900.0 and epoch B1955.0) of 502 stars in a region of about 1.5 degrees square in the Pleiades cluster, centered on Eta Tau. These coordinates have been derived from measurements of stellar images obtained with 65 exposures of various durations on 14 photographic plates with two telescopes at McCormick Observatory and Van Vleck Observatory. The plates were reduced by the plate overlap method, which resulted in a high degree of systematic accuracy in the final positions. Data in the machine version include Hertzsprung number, color index, photovisual magnitude, right ascension and declination and their standard errors, proper motion, and differences between the present position and previous works. Data for exposures, plates, and images measured, present in the published catalog, are not included in the machine version.
  ***  

['Haro G.', ' Chavira E.', ' Gonzalez G.']
The original catalog lists the flare stars discovered by different astronomical observatories over an area slightly larger than 20 square degrees in the Pleiades regions centered on Alcyone. Not all the flare stars are members of this cluster, membership indicators are provided in the catalog. The catalog, combining Tables 1 and 2 of the publication, gives the data for 1531 flares of 519 flare stars.
  ***  

['Hesser J.E.', ' Henry R.C.']
Photoelectric photometry of the K-line of calcium has been performed for the A stars of five open clusters (Hyades, Pleiades, IC 2391, IC 2602, and NGC 6475) and one association (Orion). All observations were carried out simultaneously with the field stars measurements in Paper II (II/43), with the 16-inch (40cm) and 36-inch (91cm) telescopes of the Cerro Tololo Inter-American Observatory, between May 1969 and January 1970.
  ***  

['SCHILBACH E.', ' ROBICHON N.', ' SOUCHAY J.', ' GUIBERT J.']
A catalogue of proper motions and photographic B,V magnitudes for stars up to B=19 mag within a region centered near Alcyone is presented. The catalogue is based on MAMA measurements of 8 plates taken with the Tautenburg Schmidt telescope. The survey includes ca. 14500 stars and covers a total field of about 9 square degrees. Membership probabilities, proper motions and B,V magnitudes are listed for 442 stars up to B=19 mag in the Pleiades field.
  ***  

['Mermilliod J.-C.', ' Bratschi P.', ' Mayor P.']
The analysis of CORAVEL radial velocities of 93 stars selected on the basis of their proper motion and Geneva CCD photometric observations for 57 stars have permitted to identify 25 new members in the outer part of the Pleiades. Several spectroscopic binaries have been discovered, but their membership is not clear. Two orbits with short periods have been determined, but both stars are probably non-members. The total number of member stars in the outer part of the Pleiades in the spectral range F5-K0 (0.45<B-V<0.90) is now 81 which is comparable to the number of stars known in Hertzsprung's central area (88 stars) in the same spectral domain. Therefore at least 48% of the F5-K0 main-sequence stars are located in the outer part of the cluster. And the census is probably still incomplete.
  ***  

['Bouvier J.', ' Rigaut F.', ' Nadeau D.']
This table provides the list of stars observed but not resolved during the diffraction-limited survey of G and K Pleiades dwarfs. Previously known binaries, either photometric or spectroscopic, are referenced.
  ***  

['Raboud D.', ' Mermilliod J.-C.']
On the basis of the best available member list and duplicity information, we have studied the radial distribution of 270 stars and multiple systems earlier than K0 in the Pleiades. Five new long period spectroscopic binaries have been identified from the CORAVEL observations. We have found a clear mass segregation between binaries and single stars, which is explained by the greater average mass of the multiple systems. The mass function of the single stars and primaries appears to be significantly different. While the central part of the cluster is spherical, the outer part is clearly elliptical, with an ellipticity of 0.17. The various parameters describing the Pleiades are (for a distance of 125pc): core radius r_c_=0.6 deg (1.4pc), tidal radius r_t_=7.4 (16pc), half mass radius r_m/2_=0.88 (1.9pc), harmonic radius r=1.82 (4pc). Low-mass stars (later than K0) probably extend further out and new proper motion and radial velocity surveys over a larger area and to fainter magnitudes would be very important to improve the description of the cluster structure and complete mass function.
  ***  

['Belikov A.N.', ' Hirte S.', ' Meusinger H.', ' Piskunov A.E.', ' Schilbach E.']
The luminosity function (LF) of the Pleiades cluster stars was constructed for the study of the LF fine structure related to pre-main sequence (MS) stellar evolution. Theoretical luminosity functions based on present-day pre-MS and MS stellar models were constructed and compared with observations. We tested both power- and log-normal laws describing the cluster star Initial Mass Function (IMF). Both single star formation burst- and age spread-models were examined. The agreement between the observed Pleiades colour-magnitude diagram with the new HIPPARCOS distance and the theoretical ZAMS for a normal metallicity is excellent when the model positions in the HR diagram are corrected to the helium abundance Y=0.34. The corresponding age of the cluster is logt=7.95. Three features (dips) were found in the observed cluster LF in a magnitude range M_V_=5-12mag. Two of them (at M_V_=7.5mag and 9.5mag) are assumed to be field LF features: Wielen and Kroupa dips. Theoretical models fail to reproduce them. We attributed the third (brightest) detail (the dip at M_V_=5.5mag) to the pre-MS evolution of Pleiades stars. The observed Pleiades LF corresponds in its brighter part to the standard Population I IMF. The log-normal IMF fits the observations much better than a simple power-law IMF. The brightest LF feature could be reproduced in the theoretical LF if a substantial age spread of order of several tens of Myrs is supposed to exist among the Pleiades stars.
  ***  

['Raboud D.', ' Mermilliod J.-C.']
On the basis of the best available member list and duplicity information, we have studied the radial structure of Praesepe and of the very young open cluster NGC 6231. We have found mass segregation among the cluster members and between binaries and single stars, which is explained by the greater average mass of the multiple systems. However, the degree of mass segregation for stars between 1.5 and 2.3M_{sun}_ is less pronounced in Praesepe than in the Pleiades. Furthermore, mass segregation is already present in the very young open cluster NGC 6231 although this cluster is likely still not dynamically relaxed. We discuss the implications of these results and propose a qualitative scenario for the evolution of mass segregation in open clusters. In Praesepe the mass function of single stars and primaries appears to be significantly different, like in the Pleiades. We observe an absence of ellipticity of the outer part of Praesepe.
  ***  

['Micela G.', ' Sciortino S.', ' Harnden', ' F.R.Jr.', ' Kashyap V.', ' Rosner R.', ' Prosser C.F.', ' Damiani F.', ' Stauffer J.', ' Caillault J.-P.']
In a deep X-ray survey of the Pleiades open cluster, we use the ROSAT High Resolution Imager to explore a region of the cluster formerly surveyed with the PSPC. These new observations substantially improve upon both the sensitivity and the spatial resolution for this region of the Pleiades, allowing us to detect 18 cluster members not detected before and 16 members not included in the catalogs used in previous surveys. The high sensitivity of the present observations permits us to obtain more stringent upper limits for 72 additional members and also provides sufficient numbers of stars to enable us to explore the dependence of L_x_ on stellar rotation for the slow rotators of the Pleiades. Using the new high sensitivity X-ray observations and the recent rotational measurements we discuss the activity-rotation relationship in the Pleiades solar type stars. We also present new photometric observations of optical counterparts of a number of X-ray sources detected in previous surveys but not yet identified.
  ***  

['Jeffries R.D.', ' Thurston M.R.', ' Hambly N.C.']
We present the results of a 0.86 square degree CCD photometric survey of the open cluster NGC 2516, which has an age of about 150Myr and may have a much lower metallicity than the similarly-aged Pleiades. Our BVI_c_ survey of cluster members is complete to V~20 and is used to select a preliminary catalogue of 1254 low mass (0.<M<2.0M_{sun}_) cluster candidates, of which about 70-80 percent are expected to be genuine. After applying corrections for contamination by non-members and adding data for higher mass stars from the literature, we investigate the cluster binarity, luminosity and mass function, mass segregation and total mass. We find a binary fraction of 26+/-5%, for A to M-type systems with mass ratios between 0.6 and 1, which is very similar to the Pleiades.
  ***  

['Messina S.', ' Guinan E.F.']
A long-term photometric monitoring of a selected sample of solar analogues has been carried out since early nineties as part of "The Sun in tim" project, which is aimed at a multiwavelength study of stars with solar-like global properties, but with different ages and thus at different stages of their evolution. The extended time sequence of ground-based observations collected over more than a decade as part of this program has revealed the existence of starspot cycles. Also from these data it is possible to investigate surface differential rotation of the stars. In this paper we present the photometry collected to date and report on cycles search for a selected subsample of five young single G0-G5V stars with ages between ~130Myr and 700Myr: EK Dra, {pi}^1^ UMa, HN Peg, {kappa}^1^ Cet, BE Cet. Also we include in this study the Pleiades-age (~130Myr) K0V star DX Leo (HD 82443). All the cited stars show activity cycles whose period is, furthermore, the first determined from photometric data. They are compared to those activity cycles derived from CaII H&K emission fluxes and differences are discussed. All the cycle periods, except for EK Dra, fit well the empirical relations with global stellar parameters derived from larger stellar samples. The following results are also inferred from the present study: i) the fastest rotating stars tend to have longer cycles; ii) the range in the observed cycle lengths seems to converge with stellar age from a maximum dispersion around the Pleiades' age towards the solar cycle value at the Sun's age; iii) the overall short- and long-term photometric variability increases with inverse Rossby number with very high correlation degree, indicating that the level of magnetic activity at least in photosphere is still controlled by the stellar rotation even on the longest time scales; iiii) the increase with inverse Rossby number of the long-term overall photometric variability seems to level off at the highest rotation rate, which may be interpreted as due to a saturation in the level of photospheric magnetic activity around the activity maximum.
  ***  

['Pizzolato N.', ' Maggio A.', ' Micela G.', ' Sciortino S.', ' Ventura P.']
We present the results of a new study on the relationship between coronal X-ray emission and stellar rotation in late-type main-sequence stars. We have selected a sample of 259 dwarfs in the B-V range 0.5-2.0, including 110 field stars and 149 members of the Pleiades, Hyades, {alpha} Persei, IC 2602 and IC 2391 open clusters. All the stars have been observed with ROSAT, and most of them have photometrically-measured rotation periods available. Our results confirm that two emission regimes exist, one in which the rotation period is a good predictor of the total X-ray luminosity, and the other in which a constant saturated X-ray to bolometric luminosity ratio is attained; we present a quantitative estimate of the critical rotation periods below which stars of different masses (or spectral types) enter the saturated regime.
  ***  

['Messina S.', ' Pizzolato N.', ' Guinan E.F.', ' Rodon M.']
The maximum amplitude A_max_ of spot-induced brightness variations from long-term V-band photometry and the ratio L_X_/L_bol_ between X-ray and bolometric luminosities are suitable indicators of the level of magnetic activity in the photosphere and in the corona of late-type stars, respectively. By using these activity indicators we investigate the dependence of coronal X-ray emission on the level of photospheric starspot activity in a homogeneous sample of low mass main-sequence field and cluster stars of different ages (IC 2602, IC 4665, IC 2391, {alpha} Per, Pleiades and Hyades).
  ***  

['Zickgraf F.-J.', ' Krautter J.', ' Reffert S.', ' Alcala J.M.', ' Mujica R.', ' Covino E.', ' Sterzik M.F.']
We present results of an investigation of the X-ray properties, age distribution, and kinematical characteristics of a high-galactic latitude sample of late-type field stars selected from the ROSAT All-Sky Survey (RASS). The sample comprises 254 RASS sources with optical counterparts of spectral types F to M distributed over six study areas located at |b|>~20{deg}, and Dec>=-9{deg}. A detailed study was carried out for the subsample of ~200 G, K, and M stars. Lithium abundances were determined for 179 G-M stars. Radial velocities were measured for most of the 141 G and K type stars of the sample. Combined with proper motions these data were used to study the age distribution and the kinematical properties of the sample. Based on the lithium abundances half of the G-K stars were found to be younger than the Hyades (660Myr). About 25% are comparable in age to the Pleiades (100Myr). A small subsample of 10 stars is younger than the Pleiades. They are therefore most likely pre-main sequence stars. Kinematically the PMS and Pleiades-type stars appear to form a group with space velocities close to the Castor moving group but clearly distinct from the Local Association.
  ***  

['Pillitteri I.', ' Micela G.', ' Damiani F.', ' Sciortino S.']
We report a deep X-ray survey of the young (~140Myr), rich open cluster NGC 2516 obtained with the EPIC camera on board the XMM-Newton satellite. By combining data from six observations, a high sensitivity, greater than a factor of 5 with respect to recent Chandra observations, has been achieved. Kaplan-Meier estimators of the cumulative X-ray luminosity distribution are built, statistically corrected for non members contaminants and compared to those of the nearly coeval Pleiades. The EPIC spectra of the X-ray brightest stars are fitted using optically thin model plasma with one or two thermal components. We detected 431 X-ray sources and 234 of them have as optical counterparts cluster stars spanning the entire NGC 2516 Main Sequence.
  ***  

['Groenewegen M.A.T.', ' Decin L.', ' Salaris M.', ' De Cat P.']
HD 23642 is the only known eclipsing binary in the Pleiades, and therefore of importance in determining the distance to this cluster. To use new photometric and spectroscopic data in combination with existing data in the literature in order to improve the determination of the parameters of the system, its distance and reddening. New photometric and spectroscopic data are presented for HD 23642. The spectroscopic data are ``spectrally disentangled'' using the KOREL code. The new and literature photometric and radial velocity data are simultaneously analysed using the FOTEL code to obtain the orbital solution and derive the fundamental parameters of the two stars. The distance and reddening are determined by fitting 7-colour Geneva, B,V and Stroemgren colours, and considering surface-brightness relations for the two components in (B-V) and Stroemgren c_1_-index. The preferred distance is 138.0+/-1.5pc for a reddening of E(B-V)=0.025+/-0.003. The reddening value is larger than the 0.012 adopted in the recent works on this stars by Munari et al. (2004A&A...418L..31M) and Southworth et al. (2005A&A...429..645S), and smaller than other values in the literature for the cluster reddening. The distance is in agreement with other recent works on the distance to the Pleiades. A comparison with evolutionary models suggests that the inclusion of convective core overshoot gives a much better fit to the empirical mass-radius relationship obtained from the binary analysis. Both this comparison and the "spectral disentangling" are consistent with HD 23642 having [Fe/H]=+0.06, a value determined by the most recent spectroscopical analyses of Pleiades stars.
  ***  

['Mermilliod J.-C.', ' Platais I.', ' James D.J.', ' Grenon M.', ' Cargile P.A.']
The nearby open cluster Blanco 1 is of considerable astrophysical interest for formation and evolution studies of open clusters because it is the third highest Galactic latitude cluster known. It has been observed often, but so far no definitive and comprehensive membership determination is readily available. An observing programme was carried out to study the stellar population of Blanco 1, and especially the membership and binary frequency of the F5-K0 dwarfs. We obtained radial-velocities with the CORAVEL spectrograph in the field of Blanco 1 for a sample of 148 F-G-K candidate stars in the magnitude range 10<V<14. New proper motions and UBVI CCD photometric data from two extensive surveys were obtained independently and are used to establish reliable cluster membership assignments in concert with radial-velocity data. The membership of 68 stars is confirmed on the basis of proper motion, radial velocity, and photometric criteria. Fourteen spectroscopic- and suspected binaries (2 SB2s, 9 SB1s, 3SB?) have been discovered among the confirmed members. Thirteen additional stars are located above the main sequence or close to the binary ridge, with radial velocities and proper motions supporting their membership. These are probable binaries with wide separations. Nine binaries (7 SB1 and 2 SB2) were detected among the field stars. The spectroscopic binary frequency among members is 20% (14/68); however, the overall binary rate reaches 40% (27/68) if one includes the photometric binaries. The cluster mean heliocentric radial velocity is +5.53+/-0.11km/s based on the most reliable 49 members. The Vsini distribution is similar to that of the Pleiades, confirming the age similarities between the two clusters.
  ***  

['Messina S.', ' Desidera S.', ' Tutatto M.', ' Lanzafame A.C.', ' Guinan E.F.']
Examining the angular momentum of stars and its interplay with their magnetic fields represent a promising way to probe the stellar internal structure and evolution of low-mass stars. We attempt to determine the rotational and magnetic-related activity properties of stars at different stages of evolution.We focused our attention primarily on members of clusters and young stellar associations of known ages. In this study, our targets are 6 young loose stellar associations within 100pc and with ages in the range 8-70Myr: TW Hydrae (~8Myr), beta Pictoris (~10Myr), Tucana/Horologium, Columba, Carina (~30Myr), and AB Doradus (~70Myr). Additional rotational data for alpha Persei and the Pleiades from the literature are also considered.
  ***  

['Lodieu N.', ' de Wit W.J.', ' Carraro G.', ' Moraux E.', ' Bouvier J.', ' Hambly N.C.']
Knowledge of the mass function in open clusters constitutes one way to constrain the formation of low-mass stars and brown dwarfs along with the knowledge of the frequency of multiple systems and the properties of disks. The aim of the project is to determine the shape of the mass function in the low-mass and substellar regimes in the pre-main sequence (27Myr) cluster IC4665 located at 350pc from the Sun. We have cross-matched the near-infrared photometric data from the Eighth Data Release (DR8) of the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Clusters Survey (GCS) with previous optical data obtained with the Canada-France-Hawaii (CFH) wide-field camera to improve the determination of the luminosity and mass functions in the low-mass and substellar regimes. The availability of i and z photometry taken with the CFH12K camera on the Canada France Hawaii Telescope added strong constraints to the UKIDSS photometric selection in this cluster located in a dense region of our Galaxy. We have derived the luminosity and mass functions of the cluster down to J=18.5mag, corresponding to masses of ~0.025M_{sun}_ at the distance and age of IC4665 according to theoretical models. In addition, we have extracted new candidate members down to ~20 Jupiter masses in a previously unstudied region of the cluster. We have derived the mass function over the 0.6-0.04M_{sun}_ mass range and found that it is best represented by a log-normal function with a peak at 0.25-0.16M_{sun}_, consistent with the determination in the Pleiades.
  ***  

['Maedler T.', ' Jofre P.', ' Gilmore G.', ' C Worley C.', ' Soubiran C.', ' Blanco-Cuaresma S.', ' Hawkins K.', ' Casey A.R.']
Since the release of the Hipparcos catalogue in 1997, the distance to the Pleiades open cluster has been heavily debated. The distance obtained from Hipparcos and those by alternative methods differ by 10 to 15%. As accurate stellar distances are key to understanding stellar structure and evolution, this dilemma puts the validity of some stellar evolution models into question. Using our model-independent method to determine parallaxes based on twin stars, we report individual parallaxes of 15 FGK type stars in the Pleiades in anticipation of the astrometric mission Gaia. These parallaxes give a mean cluster parallax of 7.42+/-0.09mas,which corresponds to a mean cluster distance of 134.8+/-1.7pc. This value agrees with the current results obtained from stellar evolution models.
  ***  

['Barrado D.', ' Bouy H.', ' Bouvier J.', ' Moraux E.', ' Sarro L.M.', ' Bertin E.', ' Cuillandre J.C.', ' Stauffer J.R.', ' Lillo-Box J.', ' Pollock A.']
Stellar clusters are open windows to understand stellar evolution. Specifically, the change with time and the dependence on mass of different stellar properties. As such, they are our laboratories where different theories can be tested. We try to understand the origin of the connection between lithium depletion in F, G and K stars, rotation and activity, in particular in the Pleiades open cluster. We have collected all the relevant data in the literature, including information regarding rotation period, binarity and activity, and cross-matched with proper motions, multi-wavelength photometry and membership probability from the DANCe database. In order to avoid biases, only Pleiades single members with probabilities larger than 75% have been included in the discussion. Results. The analysis confirms that there is a strong link between activity, rotation and the lithium equivalent width excess, specially for the range Lum(bol)=0.5-0.2L_{sun}_ (about K2-K7 spectral types or 0.75-0.95M_{sun}_). It is not possible to disentangle these effects but we cannot exclude that the observed lithium overabundance is partially an observational effect due to enhanced activity, due to a large coverage by stellar spots induced by high rotation rates. Since a bona fide lithium enhancement is present in young, fast rotators, both activity and rotation should play a role in the lithium problem.
  ***  

['Gaia Collaboration van Leeuwen F.', ' Vallenari A.', ' Jordi C.', ' Lindegren L.', ' Bastian U.', ' Prusti T.', ' de Bruijne J.H.J.', ' Brown A.G.A.', ' Babusiaux C.', ' Bailer-Jones C.A.L.', ' Biermann M.', ' Evans D.W.', ' Eyer L.', ' Jansen F.', ' Klioner S.A.', ' Lammers U.', ' Luri X.', ' Mignard F.', ' Panem C.', ' Pourbaix D.', ' Randich S.', ' Sartoretti P.', ' Siddiqui H.I.', ' Soubiran C.', ' Valette V.', ' Walton N.A.', ' Aerts C.', ' Arenou F.', ' Cropper M.', ' Drimmel R.', ' Hog E.', ' Katz D.', ' Lattanzi M.G.', " O'Mullane W.", ' Grebel E.K.', ' Holland A.D.', ' Huc C.', ' Passot X.', ' Perryman M.', ' Bramante L.', ' Cacciari C.', ' Castaneda J.', ' Chaoul L.', ' Cheek N.', ' De Angeli F.', ' Fabricius C.', ' Guerra R.', ' Hernandez J.', ' Jean-Antoine-Piccolo A.', ' Masana E.', ' Messineo R.', ' Mowlavi N.', ' Nienartowicz K.', ' Ordonez-Blanco D.', ' Panuzzo P.', ' Portell J.', ' Richards P.J.', ' Riello M.', ' Seabroke G.M.', ' Tanga P.', ' Thevenin F.', ' Torra J.', ' Els S.G.', ' Gracia-Abril G.', ' Comoretto G.', ' Garcia-Reinaldos M.', ' Lock T.', ' Mercier E.', ' Altmann M.', ' Andrae R.', ' Astraatmadja T.L.', ' Bellas-Velidis I.', ' Benson K.', ' Berthier J.', ' Blomme R.', ' Busso G.', ' Carry B.', ' Cellino A.', ' Clementini G.', ' Cowell S.', ' Creevey O.', ' Cuypers J.', ' Davidson M.', ' De Ridder J.', ' de Torres A.', ' Delchambre L.', " Dell'Oro A.", ' Ducourant C.', ' Fremat Y.', ' Garcia-Torres M.', ' Gosset E.', ' Halbwachs J.-L.', ' Hambly N.C.', ' Harrison D.L.', ' Hauser M.', ' Hestroffer D.', ' Hodgkin S.T.', ' Huckle H.E.', ' Hutton A.', ' Jasniewicz G.', ' Jordan S.', ' Kontizas M.', ' Korn A.J.', ' Lanzafame A.C.', ' Manteiga M.', ' Moitinho A.', ' Muinonen K.', ' Osinde J.', ' Pancino E.', ' Pauwels T.', ' Petit J.-M.', ' Recio-Blanco A.', ' Robin A.C.', ' Sarro L.M.', ' Siopis C.', ' Smith M.', ' Smith K.W.', ' Sozzetti A.', ' Thuillot W.', ' van Reeven W.', ' Viala Y.', ' Abbas U.', ' Abreu Aramburu A.', ' Accart S.', ' Aguado J.J.', ' Allan P.M.', ' Allasia W.', ' Altavilla G.', ' Alvarez M.A.', ' Alves J.', ' Anderson R.I.', ' Andrei A.H.', ' Anglada Varela E.', ' Antiche E.', ' Antoja T.', ' Anton S.', ' Arcay B.', ' Bach N.', ' Baker S.G.', ' Balaguer-Nunez L.', ' Barache C.', ' Barata C.', ' Barbier A.', ' Barblan F.', ' Barrado y Navascues D.', ' Barros M.', ' Barstow M.A.', ' Becciani U.', ' Bellazzini M.', ' Bello Garcia A.', ' Belokurov V.', ' Bendjoya P.', ' Berihuete A.', ' Bianchi L.', ' Bienayme O.', ' Billebaud F.', ' Blagorodnova N.', ' Blanco-Cuaresma S.', ' Boch T.', ' Bombrun A.', ' Borrachero R.', ' Bouquillon S.', ' Bourda G.', ' Bouy H.', ' Bragaglia A.', ' Breddels M.A.', ' Brouillet N.', ' Bruesemeister T.', ' Bucciarelli B.', ' Burgess P.', ' Burgon R.', ' Burlacu A.', ' Busonero D.', ' Buzzi R.', ' Caffau E.', ' Cambras J.', ' Campbell H.', ' Cancelliere R.', ' Cantat-Gaudin T.', ' Carlucci T.', ' Carrasco J.M.', ' Castellani M.', ' Charlot P.', ' Charnas J.', ' Chiavassa A.', ' Clotet M.', ' Cocozza G.', ' Collins R.S.', ' Costigan G.', ' Crifo F.', ' Cross N.J.G.', ' Crosta M.', ' Crowley C.', ' Dafonte C.', ' Damerdji Y.', ' Dapergolas A.', ' David P.', ' David M.', ' De Cat P.', ' de Felice F.', ' de Laverny P.', ' De Luise F.', ' De March R.', ' de Martino D.', ' de Souza R.', ' Debosscher J.', ' del Pozo E.', ' Delbo M.', ' Delgado A.', ' Delgado H.E.', ' Di Matteo P.', ' Diakite S.', ' Distefano E.', ' Dolding C.', ' Dos Anjos S.', ' Drazinos P.', ' Duran J.', ' Dzigan Y.', ' Edvardsson B.', ' Enke H.', ' Evans N.W.', ' Eynard Bontemps G.', ' Fabre C.', ' Fabrizio M.', ' Faigler S.', ' Falcao A.J.', ' Farras Casas M.', ' Federici L.', ' Fedorets G.', ' Fernandez-Hernandez J.', ' Fernique P.', ' Fienga A.', ' Figueras F.', ' Filippi F.', ' Findeisen K.', ' Fonti A.', ' Fouesneau M.', ' Fraile E.', ' Fraser M.', ' Fuchs J.', ' Gai M.', ' Galleti S.', ' Galluccio L.', ' Garabato D.', ' Garcia-Sedano F.', ' Garofalo A.', ' Garralda N.', ' Gavras P.', ' Gerssen J.', ' Geyer R.', ' Gilmore G.', ' Girona S.', ' Giuffrida G.', ' Gomes M.', ' Gonzalez-Marcos A.', ' Gonzalez-Nunez J.', ' Gonzalez-Vidal J.J.', ' Granvik M.', ' Guerrier A.', ' Guillout P.', ' Guiraud J.', ' Gurpide A.', ' Gutierrez-Sanchez R.', ' Guy L.P.', ' Haigron R.', ' Hatzidimitriou D.', ' Haywood M.', ' Heiter U.', ' Helmi A.', ' Hobbs D.', ' Hofmann W.', ' Holl B.', ' Holland G.', ' Hunt J.A.S.', ' Hypki A.', ' Icardi V.', ' Irwin M.', ' Jevardat de Fombelle G.', ' Jofre P.', ' Jonker P.G.', ' Jorissen A.', ' Julbe F.', ' Karampelas A.', ' Kochoska A.', ' Kohley R.', ' Kolenberg K.', ' Kontizas E.', ' Koposov S.E.', ' Kordopatis G.', ' Koubsky P.', ' Krone-Martins A.', ' Kudryashova M.', ' Kull I.', ' Bachchan R.K.', ' Lacoste-Seris F.', ' Lanza A.F.', ' Lavigne J.-B.', ' Le Poncin-Lafitte C.', ' Lebreton Y.', ' Lebzelter T.', ' Leccia S.', ' Leclerc N.', ' Lecoeur-Taibi I.', ' Lemaitre V.', ' Lenhardt H.', ' Leroux F.', ' Liao S.', ' Licata E.', ' Lindstrom H.E.P.', ' Lister T.A.', ' Livanou E.', ' Lobel A.', ' Loeffler W.', ' Lopez M.', ' Lorenz D.', ' MacDonald I.', ' Magalhaes Fernandes T.', ' Managau S.', ' Mann R.G.', ' Mantelet G.', ' Marchal O.', ' Marchant J.M.', ' Marconi M.', ' Marinoni S.', ' Marrese P.M.', ' Marschalko G.', ' Marshall D.J.', ' Martin-Fleitas J.M.', ' Martino M.', ' Mary N.', ' Matijevic G.', ' Mazeh T.', ' McMillan P.J.', ' Messina S.', ' Michalik D.', ' Millar N.R.', ' Miranda B.M.H.', ' Molina D.', ' Molinaro R.', ' Molinaro M.', ' Molnar L.', ' Moniez M.', ' Montegriffo P.', ' Mor R.', ' Mora A.', ' Morbidelli R.', ' Morel T.', ' Morgenthaler S.', ' Morris D.', ' Mulone A.F.', ' Muraveva T.', ' Musella I.', ' Narbonne J.', ' Nelemans G.', ' Nicastro L.', ' Noval L.', ' Ordenovic C.', ' Ordieres-Mere J.', ' Osborne P.', ' Pagani C.', ' Pagano I.', ' Pailler F.', ' Palacin H.', ' Palaversa L.', ' Parsons P.', ' Pecoraro M.', ' Pedrosa R.', ' Pentikaeinen H.', ' Pichon B.', ' Piersimoni A.M.', ' Pineau F.-X.', ' Plachy E.', ' Plum G.', ' Poujoulet E.', ' Prsa A.', ' Pulone L.', ' Ragaini S.', ' Rago S.', ' Rambaux N.', ' Ramos-Lerate M.', ' Ranalli P.', ' Rauw G.', ' Read A.', ' Regibo S.', ' Reyle C.', ' Ribeiro R.A.', ' Rimoldini L.', ' Ripepi V.', ' Riva A.', ' Rixon G.', ' Roelens M.', ' Romero-Gomez M.', ' Rowell N.', ' Royer F.', ' Ruiz-Dern L.', ' Sadowski G.', ' Sagrista Selles T.', ' Sahlmann J.', ' Salgado J.', ' Salguero E.', ' Sarasso M.', ' Savietto H.', ' Schultheis M.', ' Sciacca E.', ' Segol M.', ' Segovia J.C.', ' Segransan D.', ' Shih I.-C.', ' Smareglia R.', ' Smart R.L.', ' Solano E.', ' Solitro F.', ' Sordo R.', ' Soria Nieto S.', ' Souchay J.', ' Spagna A.', ' Spoto F.', ' Stampa U.', ' Steele I.A.', ' Steidelmueller H.', ' Stephenson C.A.', ' Stoev H.', ' Suess F.F.', ' Sueveges M.', ' Surdej J.', ' Szabados L.', ' Szegedi-Elek E.', ' Tapiador D.', ' Taris F.', ' Tauran G.', ' Taylor M.B.', ' Teixeira R.', ' Terrett D.', ' Tingley B.', ' Trager S.C.', ' Turon C.', ' Ulla A.', ' Utrilla E.', ' Valentini G.', ' van Elteren A.', ' Van Hemelryck E.', ' vanLeeuwen M.', ' Varadi M.', ' Vecchiato A.', ' Veljanoski J.', ' Via T.', ' Vicente D.', ' Vogt S.', ' Voss H.', ' Votruba V.', ' Voutsinas S.', ' Walmsley G.', ' Weiler M.', ' Weingrill K.', ' Wevers T.', ' Wyrzykowski L.', ' Yoldas A.', ' Zerjal M.', ' Zucker S.', ' Zurbach C.', ' Zwitter T.', ' Alecu A.', ' Allen M.', ' Allende Prieto C.', ' Amorim A.', ' Anglada-Escude G.', ' Arsenijevic V.', ' Azaz S.', ' Balm P.', ' Beck M.', ' Bernstein H.-H.', ' Bigot L.', ' Bijaoui A.', ' Blasco C.', ' Bonfigli M.', ' Bono G.', ' Boudreault S.', ' Bressan A.', ' Brown S.', ' Brunet P.-M.', ' Bunclark P.', ' Buonanno R.', ' Butkevich A.G.', ' Carret C.', ' Carrion C.', ' Chemin L.', ' Chereau F.', ' Corcione L.', ' Darmigny E.', ' de Boer K.S.', ' de Teodoro P.', ' de Zeeuw P.T.', ' Delle Luche C.', ' Domingues C.D.', ' Dubath P.', ' Fodor F.', ' Frezouls B.', ' Fries A.', ' Fustes D.', ' Fyfe D.', ' Gallardo E.', ' Gallegos J.', ' Gardiol D.', ' Gebran M.', ' Gomboc A.', ' Gomez A.', ' Grux E.', ' Gueguen A.', ' Heyrovsky A.', ' Hoar J.', ' Iannicola G.', ' Isasi Parache Y.', ' Janotto A.-M.', ' Joliet E.', ' Jonckheere A.', ' Keil R.', ' Kim D.-W.', ' Klagyivik P.', ' Klar J.', ' Knude J.', ' Kochukhov O.', ' Kolka I.', ' Kos J.', ' Kutka A.', ' Lainey V.', ' LeBouquin D.', ' Liu C.', ' Loreggia D.', ' Makarov V.V.', ' Marseille M.G.', ' Martayan C.', ' Martinez-Rubi O.', ' Massart B.', ' Meynadier F.', ' Mignot S.', ' Munari U.', ' Nguyen A.-T.', ' Nordlander T.', " O'Flaherty K.S.", ' Ocvirk P.', ' Olias Sanz A.', ' Ortiz P.', ' Osorio J.', ' Oszkiewicz D.', ' Ouzounis A.', ' Palmer M.', ' Park P.', ' Pasquato E.', ' Peltzer C.', ' Peralta J.', ' Peturaud F.', ' Pieniluoma T.', ' Pigozzi E.', ' Poels+ J.', ' Prat G.', " Prod'homme T.", ' Raison F.', ' Rebordao J.M.', ' Risquez D.', ' Rocca-Volmerange B.', ' Rosen S.', ' Ruiz-Fuertes M.I.', ' Russo F.', ' Sembay S.', ' Serraller Vizcaino I.', ' Short A.', ' Siebert A.', ' Silva H.', ' Sinachopoulos D.', ' Slezak E.', ' Soffel M.', ' Sosnowska D.', ' Straizys V.', ' ter Linden M.', ' Terrell D.', ' Theil S.', ' Tiede C.', ' Troisi L.', ' Tsalmantza P.', ' Tur D.', ' Vaccari M.', ' Vachier F.', ' Valles P.', ' Van Hamme W.', ' Veltz L.', ' Virtanen J.', ' Wallut J.-M.', ' Wichmann R.', ' Wilkinson M.I.', ' Ziaeepour H.', ' Zschocke S.']
The first Gaia Data Release contains the Tycho-Gaia Astrometric Solution (TGAS). This is a subset of about 2 million stars for which, besides the position and photometry, the proper motion and parallax are calculated using Hipparcos and Tycho-2 positions in 1991.25 as prior information. We investigate the scientific potential and limitations of the TGAS component by means of the astrometric data for open clusters. Mean cluster parallax and proper motion values are derived taking into account the error correlations within the astrometric solutions for individual stars, an estimate of the internal velocity dispersion in the cluster, and, where relevant, the effects of the depth of the cluster along the line of sight. Internal consistency of the TGAS data is assessed. . Values given for standard uncertainties are still inaccurate and may lead to unrealistic unit-weight standard deviations of least squares solutions for cluster parameters. Reconstructed mean cluster parallax and proper motion values are generally in very good agreement with earlier Hipparcos-based determination, although the Gaia mean parallax for the Pleiades is a significant exception. We have no current explanation for that discrepancy. Most clusters are observed to extend to nearly 15 pc from the cluster centre, and it will be up to future Gaia releases to establish whether those potential cluster-member stars are still dynamically bound to the clusters. The Gaia DR1 provides the means to examine open clusters far beyond their more easily visible cores, and can provide membership assessments based on proper motions and parallaxes. A combined HR diagram shows the same features as observed before using the Hipparcos data, with clearly increased luminosities for older A and F dwarfs.
  ***  

['Frasca A.', ' Guillout P.', ' Klutsch A.', ' Freire Ferrero R.', ' Marilli E.', ' Biazzo K.', ' Gandolfi D.', ' Montes D.']
Star formation in the solar neighborhood is mainly traced by young stars in open clusters, associations, and in the field, which can be identified, for example, by their X-ray emission. The determination of stellar parameters for the optical counterparts of X-ray sources is crucial for a full characterization of these stars. This work extends the spectroscopic study of the RasTyc sample, obtained by the cross-correlation of the TYCHO and ROSAT All-Sky Survey catalogs, to stars fainter than V=9.5mag and aims to identify sparse populations of young stars in the solar neighborhood. We acquired 625 high-resolution spectra for 443 presumably young stars with four different instruments in the northern hemisphere. The radial and rotational velocity (vsini) of our targets were measured by means of the cross-correlation technique, which is also helpful to discover single-lined (SB1), double-lined spectroscopic binaries (SB2), and multiple systems. We used the code ROTFIT to perform an MK spectral classification and to determine the atmospheric parameters (Teff, logg, [Fe/H]) and and vsini of the single stars and SB1 systems. For these objects, we used the spectral subtraction of slowly rotating templates to measure the equivalent widths of the H{alpha} and LiI-6708A lines, which enabled us to derive their chromospheric activity level and lithium abundance. We made use of Gaia DR1 parallaxes and proper motions to locate the targets in the HR diagram and to compute the space velocity components of the youngest objects. We find a remarkable percentage (at least 35%) of binaries and multiple systems. On the basis of the lithium abundance, the sample of single stars and SB1 systems appears to be mostly (about 60%) composed of stars younger than the members of the UMa cluster. The remaining sources are in the age range between the UMa and Hyades clusters (about 20%) or older (20%). In total, we identify 42 very young (PMS-like) stars, which lie above or very close to the Pleiades upper envelope of the lithium abundance. A significant percentage (about 12%) of evolved stars (giants and subgiants) is also present in our sample. Some of these stars are also lithium rich (A(Li)>1.4).
  ***  

['Bouvier J', ' Barrado D.', ' Moraux E.', ' Stauffer J.', ' Rebull L.', ' Hillenbrand L.', ' Bayo A.', ' Boisse I.', ' Bouy H.', ' DiFolco E.', ' Lillo-Box J.', ' Morales Calderon M.']
The evolution of lithium abundance over a star's lifetime is indicative of transport processes operating in the stellar interior. Aims. We revisit the relationship between lithium content and rotation rate previously reported for cool dwarfs in the Pleiades cluster. Methods. We derive new LiI 670.8nm equivalent width measurements from high-resolution spectra obtained for low-mass Pleiades members. We combine these new measurements with previously published ones, and use the Kepler/K2 rotational periods recently derived for Pleiades cool dwarfs to investigate the lithium-rotation connection in this 125Myr-old cluster. Results. The new data confirm the correlation between lithium equivalent width and stellar spin rate for a sample of 51 early K-type members of the cluster, where fast rotating stars are systematically lithium-rich compared to slowly rotating ones. The correlation is valid for all stars over the (J-Ks) color range 0.50-0.70mag, corresponding to a mass range from about 0.75 to 0.90M_{sun}_, and may extend down to lower masses. Conclusions. We argue that the dispersion in lithium equivalent widths observed for cool dwarfs in the Pleiades cluster reflects an intrinsic scatter in lithium abundances, and suggest that the physical origin of the lithium dispersion pattern is to be found in the pre-main sequence rotational history of solar-type stars.
  ***  

['Fritzewski D.J.', ' Barnes S.A.', ' James D.J.', ' Geller A.M.', ' Meibom S.', ' Strassmeier K.G.']
NGC 3532 is an extremely rich open cluster embedded in the Galactic disc, hitherto lacking a comprehensive, documented membership list. We provide membership probabilities from new radial velocity observations of solar-type and low-mass stars in NGC 3532, in part as a prelude to a subsequent study of stellar rotation in the cluster. Using extant optical and infra-red photometry we constructed a preliminary photometric membership catalogue, consisting of 2230 dwarf and turn-off stars. We selected 1060 of these for observation with the AAOmega spectrograph at the 3.9m Anglo-Australian Telescope and 391 stars for observations with the Hydra-South spectrograph at the 4m Victor Blanco Telescope, obtaining spectroscopic observations over a decade for 145 stars. We measured radial velocities for our targets through cross-correlation with model spectra and standard stars, and supplemented them with radial velocities for 433 additional stars from the literature. We also measured logg, Teff, and [Fe/H] from the AAOmega spectra. The radial velocity distribution emerging from the observations is centred at 5.43+/-0.04km/s and has a width (standard deviation) of 1.46km/s. Together with proper motions from Gaia DR2 we find 660 exclusive members, of which five are likely binary members. The members are distributed across the whole cluster sequence, from giant stars to M dwarfs, making NGC~3532 one of the richest Galactic open clusters known to date, on par with the Pleiades. From further spectroscopic analysis of 153 dwarf members we find the metallicity to be marginally sub-solar, with [Fe/H]=-0.07+/-0.10. We confirm the extremely low reddening of the cluster, E_B-V_=0.034+/-0.012mag, despite its location near the Galactic plane. Exploiting trigonometric parallax measurements from Gaia DR2 we find a distance of 484^+35^_-30_pc [(m-M)_0_=8.42+/-0.14mag]. Based on the membership we provide an empirical cluster sequence in multiple photometric passbands. A comparison of the photometry of the measured cluster members with several recent model isochrones enables us to confirm the 300Myr cluster age. However, all of the models evince departures from the cluster sequence in particular regions, especially in the lower mass range.
  ***  

['Lodieu N.', ' Perez-Garrido A.', ' Smart R.L.', ' Silvotti', ' R.']
Our scientific goal is to provide revised membership lists of the alpha Per, Pleiades, and Praesepe clusters exploiting the second data release of Gaia and produce five-dimensional maps ({alpha}, {delta}, {pi}, {mu}_{alpha}_cos{delta}, {mu}_{delta}_) of these clusters. We implemented the kinematic method combined with the statistical treatment of parallaxes and proper motions to identify astrometric member candidates of three of the most nearby and best studied open clusters in the sky. We cross-correlated the Gaia catalogue with large-scale public surveys to complement the astrometry of Gaia with multi-band photometry from the optical to the mid-infrared. We identified 517, 1248, and 721 bona fide astrometric member candidates inside the tidal radius of alpha Per, the Pleiades, and Praesepe, respectively. We cross-matched our final samples with catalogues from previous surveys to address the level of completeness. We update the main physical properties of the clusters, including mean distance and velocity, as well as core, half-mass, and tidal radii. We infer updated ages from the white dwarf members of the Pleiades and Praesepe. We derive the luminosity and mass functions of the three clusters and compare them to the field mass function. We compute the positions in space of all member candidates in the three regions to investigate their distribution in space. We provide updated distances and kinematics for the three clusters. We identify a list of members in the alpha Per, Pleiades, and Praesepe clusters from the most massive stars all the way down to the hydrogen-burning limit with a higher confidence and better astrometry than previous studies. We produce complete 5D maps of stellar and substellar bona fide members in these three regions. The photometric sequences derived in several colour-magnitude diagrams represent benchmark cluster sequences at ages from 90 to 600Myr. We note the presence of a stream around the Pleiades cluster extending up to 40 pc from the cluster centre.
  ***  

['Roeser S.', ' Schilbach E.']
Within a sphere of 400pc radius around the Sun, we search for members of the Pisces-Eridanus (Psc-Eri) stellar stream in the Gaia Data Release 2 DR2) data set. We compare basic astrophysical characteristics of the stream with those of the Pleiades. We used a modified convergent-point method to identify stars with 2D - velocities consistent with the space velocity of the Psc-Eri stream and the Pleiades, respectively. We found 1387 members of the Psc-Eri stream in a G-magnitude range from 5.1mag to 19.3mag at distances between 80 and 380pc from the Sun. The stream has a nearly cylindrical shape with a length of at least 700pc and a thickness of 100pc. The accumulated stellar mass of the 1387 members amounts to about 770M_{sun}_, and the stream is gravitationally unbound. For the stream we found an age of about 135Myr. In many astrophysical properties Psc-Eri is comparable to the open cluster M45 (the Pleiades): in its age, its luminosity function (LF), its present-day mass function (PDMF) as well as in its total mass. Nonetheless, the two stellar ensembles are completely unlike in their physical appearance. We cautiously give two possible explanations for this disagreement: (i) the star-formation efficiency in their parental molecular clouds was higher for the Pleiades than for Psc-Eri or/and (ii) the Pleiades had a higher primordial mass segregation immediately after the expulsion of the molecular gas of the parental cloud.
  ***  

['Miret-Roig N.', ' Huelamo N.', ' Bouy H.']
Debris discs orbiting young stars are key to understand dust evolution and the planetary formation process.We take advantage of a recent membership analysis of the 30Myr nearby open cluster IC 4665 based on the Gaia and DANCe surveys to revisit the disc population of this cluster. We aim to study the disc population of IC 4665 using Spitzer (MIPS and IRAC) and WISE photometry. We use several colour-colour diagrams with empirical photospheric sequences to detect the sources with an infrared excess. Independently, we also fit the spectral energy distribution (SED) of our debris disc candidates with the Virtual Observatory SED analyser (VOSA) which is capable of automatically detecting infrared excesses and provides effective temperature estimates. We find six candidates debris disc host-stars (five with MIPS and one with WISE) and two of them are new candidates. We estimate a disc fraction of 24+/-10% for the B-A stars, where our sample is expected to be complete. This is similar to what has been reported in other clusters of similar ages (Upper Centaurus Lupus, Lower Centaurus Crux, the $\beta$ Pictoris moving group, and the Pleiades). For solar type stars we find a disk fraction of 9+/-9%, lower than that observed in regions with comparable ages. Our candidates debris disc host-stars are excellent targets to be studied with ALMA or the future James Webb Space Telescope (JWST).
  ***  

['Fritzewski D.J.', ' Barnes S.A.', ' James D.J.', ' Strassmeier K.G.']
We wish to measure the cool star rotation period distribution for the Pleiades-age rich open cluster NGC 2516 and use it to determine whether cluster-to-cluster variations exist in otherwise identical open clusters. We obtained 42d-long time-series CCD photometry of NGC 2516 in the V and Ic filters using the Yale 1m telescope at CTIO and performed a number of related analyses, including PSF-based time-series photometry. Our data are complemented with additional information from several photometric datasets, literature radial velocities, and Gaia DR2 astrometry. All available data are used to construct an integrated membership list for NGC 2516, containing 844 stars in our ~1 degree field of view. We derived 308 rotation periods for late-F to mid-M cluster members from our photometry. We identified an additional 247 periodic M dwarf stars from a prior study as cluster members, and used these to construct a 555-star rotation period distribution for NGC 2516. The colour-period diagram (in multiple colours) has almost no outliers and exhibits the anticipated triangular shape, with a diagonal slow rotator sequence that is preferentially occupied by the warmer stars along with a flat fast rotator sequence that is preferentially populated by the cooler cluster members. We also find a group of extremely slowly rotating M dwarfs (10d<P<23d), forming a branch in the colour-period diagram which we call the 'extended slow rotator sequence'. This, and other features of the rotational distribution can also be found in the Pleiades, making the colour-period diagrams of the two clusters nearly indistinguishable. A comparison with the well-studied (and similarly aged) open cluster M 35 indicates that the cluster's rotational distribution is also similarly indistinguishable from that of NGC 2516. Those for the open clusters M 50 and Blanco 1 are similar, but data issues for those clusters make the comparisons somewhat more ambiguous. Nevertheless, we demonstrate the existence of a representative zero-age main sequence (ZAMS) rotational distribution and provide a simple colour-independent way to represent it. We perform a detailed comparison of the NGC 2516 rotation period data with a number of recent rotational evolution models. Using X-ray data from the literature, we also construct the first rotation-activity diagram for solar-type stars in NGC 2516, one that we find is essentially indistinguishable from those for the Pleiades and Blanco 1. The two clusters NGC 2516 and Pleiades can be considered twins in terms of stellar rotation and related properties (and M 35, M 50, and Blanco 1 are similar), suggesting that otherwise identical open clusters also have intrinsically similar cool star rotation and activity distributions.
  ***  

['Fritzewski D.J.', ' Barnes S.A.', ' James D.J.', ' Strassmeier K.G.']
A very rich cluster intermediate in age between the Pleiades (150Myr) and the Hyades (600Myr) is needed to probe the rotational evolution, especially the transition between fast and slow rotation that occurs between the two ages. We study the rich 300Myr-old open cluster NGC 3532 to probe this important transition and to provide constraints on angular momentum loss. Measuring the rotation periods builds on our prior work of providing spectroscopic membership information for the cluster, and it supports the chromospheric activity measurements of cluster stars that we provide in a companion paper. Using 42d-long photometric time series observations obtained with the Yale 1m telescope at CTIO, we measured rotation periods for members of NGC 3532 and compared them with the predictions of angular momentum evolution models. We directly measured 176 photometric rotation periods for the cluster members. An additional 113 photometric rotation periods were identified using activity information, described fully in the companion paper, resulting in a total sample containing 279 rotation periods for FGKM stars in NGC 3532. The colour-period diagram constructed from this rich data set shows a well-populated and structured slow rotator sequence, and a fast rotator sequence evolved beyond zero-age main sequence age whose stars are in transition from fast to slow rotation. The slow rotator sequence itself is split into slightly slower and faster rotators, a feature we trace to photometric binary status. We also identify an extended slow rotator sequence extending to P~32d, apparently the analogue of the one we previously identified in NGC 2516. We compare our period distribution to rotational isochrones in colour-period space and find that all considered models have certain shortcomings. Using more detailed spin-down models, we evolve the rotation periods of the younger NGC 2516 forward in time and find that the spindown of the models is too aggressive with respect to the slow rotators. In contrast, stars on the evolved fast rotator sequence are not spun down strongly enough by these models. Our observations suggest a shorter crossing time for the rotational gap, one we estimate to be ~80Myr for early-K dwarfs.
  ***  

['Messina S.', ' Nardiello D.', ' Desidera S.', ' Baratella M.', ' Benatti S.', ' Biazzo K.', " D'Orazi V."]
Gyrochronology is one of the methods currently used to estimate the age of stellar open clusters. Hundreds of new clusters, associations, and moving groups unveiled by Gaia and complemented by accurate rotation period measurements provided by recent space missions such as Kepler and TESS are allowing us to significantly improve the reliability of this method. Aims. We use gyrochronology, that is, the calibrated age-mass-rotation relation valid for low-mass stars, to measure the age of the recently discovered moving group Group X. We extracted the light curves of all candidate members from the TESS full frame images and measured their rotation periods using different period search methods. Results. We measured the rotation period of 168 of a total of 218 stars and compared their period-colour distribution with those of two age-benchmark clusters, the Pleiades (125Myr) and Praesepe (625Myr), as well as with the recently characterised open cluster NGC 3532 (300Myr). As result of our analysis, we derived a gyro age of 300+/-60Myr. We also applied as independent methods the fitting of the entire isochrone and of the three brightest candidate members individually with the most precise stellar parameters, deriving comparable values of 250 Myr and 290 Myr, respectively. Our dating of Group X allows us to definitively rule out the previously proposed connection with the nearby but much older Coma Berenices cluster.
  ***  

['Cole-Kodikara E.', ' Barnes S.', ' Weingrill J.', ' Granzer T.']
Open clusters serve as a useful tool for calibrating models of the relationship between mass, rotation, and age for stars with an outer convection zone due to the homogeneity of the stars within the cluster. Cluster to cluster comparisons are essential to determine whether the universality of spin-down relations holds. NGC 6709 is chosen as a more distant representative Pleiades-age cluster for which no rotation periods of members have previously been obtained. This cluster is at a distance of over 1 kpc and has two red giant members. Isochrones place the age of the cluster at around 150Myr, or approximately the same age as the Pleiades. Photometry is obtained over a multi-month observing season at the robotic observatory for STELLar Activity (STELLA). After basic processing, point- spread function photometry was derived using Daophot II, and a suite of related software allowed us to create time series of relative magnitude changes for each star. Four time series analysis methods are then applied to these light curves to obtain rotation periods for members stars. We obtain for the first time rotation periods for 45 FGK cluster members of NGC 6709. We plot the Gaia DR3 colors of the member stars against their rotation periods and find a slow-rotating sequence with increasing rotation periods towards redder stars and a smaller clump of rapid rotators that have not yet joined this sequence. NGC 6709 has rotation periods very similar to that of another Pleiades-age open cluster, NGC 2516.
  ***  

['Brandner W.', ' Calissendorff P.', ' Kopytova T.']
The Gaia astrophysical parameters inference system (Apsis) provides astrophysical parameter estimates for several to hundreds of millions of stars. Aims. We aim to benchmark Gaia DR3 Apsis. We compiled approximately 1500 bona fide single stars in the Hyades and Pleiades open clusters for validation of PARSEC isochrones, and for comparison with Apsis estimates. PARSEC stellar isochrones in the Gaia photometric system enable us to assign average ages and metallicities to the clusters, and mass, effective temperature, luminosity, and surface gravity to the individual stars. Apsis does not recover the single-age, single-metallicity characteristic of the cluster populations. Ages assigned to cluster members seemingly follow the input template for Galactic populations, with earlier-type stars being systematically assigned younger ages than later-type stars. Cluster metallicities are underestimated by 0.1 to 0.2dex. Effective temperature estimates are in general reliable. Surface gravity estimates reveal strong systematic errors for specific ranges of the Gaia BP-RP colours. We caution that Gaia DR3 Apsis estimates can be subject to significant systematic uncertainties. Some of the Apsis estimates, such as metallicity, might only be meaningful for statistical studies of the time-averaged Galactic stellar population, but are not recommended to be used for individual stars.
  ***  

['Zerjal M.', ' Lodieu N.', ' Perez-Garrido A.', ' Olivares J.', ' Bejar V.J.S.', ' Martin E.L.']
Open clusters are groups of coeval stars sharing properties such as distance and metallicity, and they are key to understanding stellar evolution. Our main goal is to study the evolution of open clusters with a special focus on the universality of the luminosity function. We applied an upgraded version of the convergent point technique on about 50 open clusters. The selection of cluster members was based purely on the exquisite astrometry of the Gaia DR3 and Hipparcos catalogues in the five-dimensional or full six-dimensional space. We present updated lists of bona fide members of ~50 open clusters within 500pc and younger than 1Gyr, exploiting the full depth of the third Gaia data release complemented by Hipparcos at the bright end, excluding regions in the Galactic plane. Our catalogues also are complemented by optical and infrared photometry from the major large-scale public surveys. All the data will be made available on a dedicated webpage with interactive plots and a direct link to Aladin and Vizier hosted at the Centre de Donnees de Strasbourg. We derived luminosity functions for all bound clusters and compared them in three age groups of ~50Myr, ~150Myr, and ~600Myr, discussing similarities and differences to constrain their dynamical evolution. Luminosity functions of clusters at 50Myr are more likely similar to each other and show a greater degree of similarity than older clusters. We explain this observation with the universal luminosity function within the volume of our sample (500pc). Luminosity functions of clusters with ages similar to the Pleiades or Hyades are more diverse, perhaps due to internal dynamical evolution, but more work is needed to provide additional evidence.
  ***  

['Hambly N.C.', ' Hawkins M.R.S.', ' Jameson R.F.']
A proper motion membership list is presented for the lower mass stars in the Pleiades open cluster based on a survey of about a 5x5{deg} area around the cluster center. Finder charts prepared from an R passband Schmidt plate are given. Photographic R and I photometry is given for all stars; where possible a V magnitude is also listed. The photometry is accurate to about 0.1mag.
  ***  

['Panagi P.M.', " O'Dell M.A."]
We present the results of H{alpha}(6562A) and Li I(6708A) observations of 114 low-mass stars of the young open cluster Blanco 1. We also present observations of 30 stars in Ca II(K). This work extends the first Blanco 1 spectroscopic study of Panagi et al. (1994A&A...285..233D). From a sample of four well-studied clusters, including Blanco 1, we find that the fraction of H{alpha} emission-line stars amongst K dwarfs is a good indicator of relative age, with a smaller fraction indicative of older age. Blanco 1 shows a relatively small fraction of emitters, inconsistent with previous age estimates for the cluster. We estimate the cluster age to to be 90+/-25Myr, slightly older than the Pleiades. The method is shown to be more sensitive to age than lithium and a useful alternative to other age measurement techniques. The variation of H{alpha} with (B-V) is similar to that observed in the older solar neighbourhood dwarfs, suggesting that, at least for the absorption-line stars, the contribution of stellar rotation to the equivalent width is unclear. We combine both spectroscopy and photometry to revise cluster membership and give accurate positions for all these stars.
  ***  

['Rolleston W.R.J.', ' Byrne P.B.']
New 4-colour BV(RI)_KC_ CCD photometry to a limiting magnitude of V=~19 is presented for 1428 objects observed towards the direction of the young, open cluster IC 2391. We observed 36 (2'x3') fields within 17arcmin of the nominal cluster core. By fitting the theoretical isochrones of D'Antona & Mazzitelli (1994ApJS...90..467D) to a combination of colour-magnitude and colour-colour diagrams, we have identified 17 stars as probable cluster members with a further 85 stars as possible members. The brightness distribution of low-mass members is compared with the luminosity function observed for the Pleiades and we estimate that the contamination due to background giants should be small.
  ***  

['Li J.Z.', ' Hu J.Y.']
We present results of an extensive search for weak-line T Tauri stars (WTTS) in the outskirts of the Taurus-Auriga molecular cloud on the basis of the ROSAT All-Sky Survey Bright Source Catalog (Cat. <IX/10>). Our surveyed region extends from 2h 40m to 5h 40m in right ascension and from 10deg to 40deg in declination, with the central part of Taurus-Auriga(4h<{alpha}<5h, 15deg<{delta}<34deg), accomplished by Wichmann et al. (1996, Cat. <J/A+A/312/439>), excluded. Within a sky coverage of about 10$^{3}$ square degrees, 219 X-ray sources fullfill the criteria for selecting program sources suggested by Neuhauser et al. (1995A&A...295L...5N) and 164 of these X-ray sources were found to have at least one optical counterpart with E magnitude brighter than 16. Low-resolution spectroscopic observation has been carried out in order to discard early type stars and galaxies from the sample, additional intermediate-resolution spectra of a sub-sample of 156 late type optical counterparts were obtained for spectral classification and for the calculation of the equivalent width of H{alpha} emission and LiI line absorption at 6707{AA}. Excluding 2 previously identified WTTS, a total of 75 new candidate WTTS and one possible classical T Tauri star have been discovered in our study. The majority of the newly found Li-rich optical counterparts are believed to b e PMS stars rather than ZAMS stars as those of the Pleiades.
  ***  

['Kinman T.D.', ' Suntzeff N.B.', ' Kraft R.P.']
A complete sample of blue horizontal branch (BHB) stars in the magnitude range 13.0<V<16.5 is isolated in two Galactic fields that have previously been searched for RR Lyrae variables: SA 57 in the Northern Polar Cap and the Lick Astrograph field RR 7 in the Anticenter (l=183{deg}, b=+37{deg}). These BHB stars are a subset of the AF stars found in the Case Low-Dispersion Northern Survey; lists of these AF stars were made available by the late Nick Sanduleak. The completeness of the sample was confirmed by reference to the photometric survey of SA 57 by Stobie & Ishida (1987AJ93..... 624S) that is complete to fainter than V=18. In the color range 0.00<(B-V)_0_<+0.20, we can distinguish the BHB stars among these AF stars by comparing them both with well known local field horizontal branch (FHB) stars and also the BHB members of the halo globular clusters M3 and M92. The criteria for this comparison include (1) a (u-B)_K_ color index (derived from photoelectric observations using the Stromgren u filter and the Johnson B and V filters) that measures the size of the Balmer jump, (2) a spectrophotometric index A that measures the steepness of the Balmer jump, and (3) a parameter D_0.2_ that is the mean width of the H{gamma} and H{delta} Balmer lines measured at 20 percent of the continuum level. These criteria give consistent results in separating BHB stars from higher gravity main sequence AF stars in the color range 0.00<(B-V)_0_<+0.20. All three photometric and spectrophotometric criteria were measured for 35 stars in the SA 57 field and 37 stars in the RR 7 field that are in the color range (B-V)_0_<+0.23 and in the magnitude range 13.0<V<16.5. For a small number of additional stars only (u-B)_K_ was obtained. Among the AF stars that are fainter than B=13 and bluer than (B-V)_0_=+0.23, about half of those in the SA 57 field and about one third of those in the lower latitude RR 7 field are BHB stars. Isoabundance contours were located empirically in plots of the pseudoequivalent width versus (B-V)_0_ for the lines of Mg II A4481{AA}, Ca II A3933 {AA} and Fe I A4272{AA}. Solar abundances were defined by the data from main sequence stars in the Pleiades and Coma open clusters. Data from the BHB stars in M3 and M92 defined the [Fe/H]=1.5 and -2.2 isoabundance contours, respectively. Metallicities of all stars were estimated by interpolating the measured pseudoequivalent widths in these diagrams at the observed (B-V)_0_. The distribution of [Fe/H] found for the BHB stars in this way is very similar to that which we found for the RR Lyrae stars in the same fields using the Preston AS method. The space densities of these BHB stars were analyzed both separately and together with earlier observations of field BHB stars given by Arnold & Gilmore (1992MNRAS.257..225A), Sommer-Larsen & Christensen (1986MNRAS.219..537S), and Preston et al. (1991ApJ...375..121P). This analysis supports a two-component model for the halo of our Galaxy that is similar in many respects to that proposed by Hartwick [The Galaxy (Reidel, Dordrecht 1987)] although our discussion refers only to the region outside the solar circle. For Z>=35kpc, a classical spherical halo dominates which follows a R_gal_^-3.5^ space-density law and which has a HB morphology like that of the globular cluster M3 (i.e., approximately equal numbers of BHB and RR Lyrae stars). Closer to the galactic plane, there is an additional component with a much flatter galactic distribution (scale height ~2.2kpc near the Sun). The stars of the two components do not have significantly different metallicity distributions but do have slightly different distributions of the A parameter which measures the steepness of the Balmer jump; this is the only physical criterion (independent of spatial or kinematic considerations) which distinguishes between the two components. If present estimates of the local RR Lyrae star space density are correct, then the ratio of BHB stars to RR Lyrae stars is higher in the flatter halo component. The flat component would then have a bluer HB morphology (which could be interpreted as making it older) than the spherical component. In the solar neighborhood about 80 percent of the BHB stars come from the flat component and about 20 percent from the spherical component. More than half of the AF stars with V>13.0 and (B-V)_0_<+0.23 are not BHB stars but have surface gravities that are more like those expected for main sequence stars. Their measured metallicities lie in the range -0.2<[Fe/H]<-2.3. The more metal-poor of these stars are probably similar to the blue metal-poor stars that have been discussed by Preston et al. (1994AJ....108..538P) which, while they probably include globular cluster blue stragglers as a subset, must also comprise stars of other types.
  ***  

['Prosser C.F.', ' Stauffer J.R.', ' Caillault J.-P.', ' Balachandran S.', ' Stern R.A.', ' Randich S.']
A ROSAT X-ray survey, with complementary optical photometry, of the open cluster NGC 6475 has enabled the detection of ~50 late-F to K0 and ~70 K/M dwarf new candidate members, providing the first reliable detection of low-mass stars in this low galactic latitude, 220Myr old cluster. The X-ray observations reported here have a typical limiting sensitivity of L_X_ ~ 10^29^erg/s. The detection frequency of early type cluster members is consistent with the hypothesis that the X-ray emitting early type stars are binary systems with an unseen, low-mass secondary producing the X-rays. The ratio between X-ray and bolometric luminosity among NGC 6475 members saturates at a spectral-type/color which is intermediate between that in much younger and in much older clusters, consistent with rotational spindown of solar-type stars upon their arrival on the ZAMS. The upper envelope of X-ray luminosity as a function of spectral type is comparable to that of the Pleiades, with the observed spread in X-ray luminosity among low-mass members being likely due to the presence of binaries and relatively rapid rotators. However, the list of X-ray selected candidate members is likely biased against low-mass, slowly rotating single stars. While some preliminary spectroscopic information is given in an appendix, further spectroscopic observations of the new candidate members will aid in interpreting the coronal activity among solar-type NGC 6475 members and their relation to similar stars in older and younger open clusters.
  ***  

['Clampitt L.', ' Burstein D.']
Spectrophotometry is presented for 237 stars in 7 nearby open clusters: Hyades, Pleiades, Alpha Persei, Praesepe, Coma Berenices, IC 4665, and M39. The observations were taken by Lee McDonald and David Burstein using the Wampler single-channel scanner on the Crossley 0.9m telescope at Lick Observatory from 1973 July through 1974 December. Sixteen bandpasses spanning the spectral range 3500-7780{AA} were observed for each star, with bandwidths 32, 48, or 64{AA}. Data are standardized to the Hayes-Latham system to mutual accuracy of 0.016mag per passband. The accuracy of the spectrophotometry is assessed in three ways on a star-by-star basis. First, comparisons are made with previously published spectrophotometry for 19 stars observed in common. Second, (B-V) colors and uvby colors are compared for 236 stars and 221 stars, respectively. Finally, comparisons are made for 200 main sequence stars to the spectral synthesis models of Kurucz, fixing logg=4.0 and [Fe/H]=0.0, and only varying effective temperature. The accuracy of tests using uvby colors and the Kurucz models are shown to track each other closely, yielding an accuracy estimate (1{sigma}) of 0.01mag for the 13 colors formed from bandpasses longward of the Balmer jump, and 0.02mag for the 3 colors formed from the three bandpasses below the Balmer jump. In contrast, larger scatter is found relative to the previously published spectrophotometry of Bohm-Vitense & Johnson (1977ApJS...35..461B) (16 stars in common) and Gunn & Stryker (1983, Cat. <III/88>) (3 stars). We also show that the scatter in the fits of the spectrophotometric colors and the uvby filter colors is a reasonable way to identify the observations of which specific stars are accurate to 1{sigma}, 2{sigma}, .... As such, the residuals from both the filter color fits and the Kurucz model fits are tabulated for each star where it was possible to make a comparison, so users of these data can choose stars according to the accuracy of the data that is appropriate to their needs. The very good agreement between the models and these data verifies the accuracy of these data, and also verifies the usefulness of the Kurucz models to define spectrophotometry for stars in this temperature range (>5000K). These data define accurate spectrophotometry of bright, open cluster stars that can be used as a secondary flux calibration for CCD-based spectrophotometric surveys. (c) 1997 American Astronomical Society.
  ***  

['Stassun K.G.', ' Mathieu R.D.', ' Mazeh T.', ' Vrba F.J.']
We report rotation periods for 254 stars in an area 40'x80' centered on the Orion Nebula. We show that these stars are likely members of the young (~10^6^yr) Orion OBIc/d association. The rotation period distribution we determine, which is sensitive to periods 0.1<P<8days, shows a sharp cutoff for periods P<0.5days, corresponding to breakup velocity for these stars. Above 0.5days the distribution is consistent with a uniform distribution; we do not find evidence for a "gap" of periods at 4-5days. We find signatures of active accretion among stars at all periods; active accretion does not occur preferentially among slow rotators in our sample. We find no correlation between rotation period and near-IR signatures of circumstellar disks. In addition, we show that the distribution of vsini among stars in our sample bears striking resemblance to that of low-mass Pleiades stars. We discuss the implications of our findings for the evolution of stellar angular momentum during the pre-main-sequence phase. We argue that all stars in our sample must still deplete angular momentum by factors of roughly 5-10, if they are to preserve their vsini distribution over approximately the next 100Myr. We consider in detail whether our findings are consistent with disk-regulated stellar rotation. We do not find observational evidence that magnetic disk-locking is the dominant mechanism in angular momentum evolution during the premain-sequence phase.
  ***  

['Kamai B.L.', ' Vrba F.J.', ' Stauffer J.R.', ' Stassun K.G.']
We present new BVI_C_ photometry for 350 Pleiades proper motion members with 9<V<~17. Importantly, our new catalog includes a large number of K- and early M-type stars, roughly doubling the number of low-mass stars with well-calibrated Johnson/Cousins photometry in this benchmark cluster. We combine our new photometry with existing photometry from the literature to define a purely empirical isochrone at Pleiades age ({approx}100Myr) extending from V=9 to 17. We use the empirical isochrone to identify 48 new probable binaries and 14 likely nonmembers. The photometrically identified single stars are compared against their expected positions in the color-magnitude diagram (CMD). At 100Myr, the mid K and early M stars are predicted to lie above the zero-age main sequence (ZAMS) having not yet reached the ZAMS. We find in the B-V versus V CMD that mid K and early M dwarfs are instead displaced below (or blueward of) the ZAMS. Using the stars' previously reported rotation periods, we find a highly statistically significant correlation between rotation period and CMD displacement, in the sense that the more rapidly rotating stars have the largest displacements in the B-V CMD.
  ***  

['Rebull L.M.', ' Stauffer J.R.', ' Bouvier J.', ' Cody A.M.', ' Hillenbrand L.A.', ' Soderblom D.R.', ' Valenti J.', ' Barrado D.', ' Bouy H.', ' Ciardi D.', ' Pinsonneault M.', ' Stassun K.', ' Micela G.', ' Aigrain S.', ' Vrba F.', ' Somers G.', ' Christiansen J.', ' Gillen E.', ' Collier Cameron A.']
Young (125Myr), populous (>1000 members), and relatively nearby, the Pleiades has provided an anchor for stellar angular momentum models for both younger and older stars. We used K2 to explore the distribution of rotation periods in the Pleiades. With more than 500 new periods for Pleiades members, we are vastly expanding the number of Pleiades with periods, particularly at the low-mass end. About 92% of the members in our sample have at least one measured spot-modulated rotation period. For the ~8% of the members without periods, non-astrophysical effects often dominate (saturation, etc.), such that periodic signals might have been detectable, all other things being equal. We now have an unusually complete view of the rotation distribution in the Pleiades. The relationship between P and (V-K_s_)_0_ follows the overall trends found in other Pleiades studies. There is a slowly rotating sequence for 1.1<~(V-K_s_)_0_<~3.7 and a primarily rapidly rotating population for (V-K_s_)_0_>~5.0. There is a region in which there seems to be a disorganized relationship between P and (V-K_s_)_0_ for 3.7<~(V-K_s_)_0_<~5.0. Paper II continues the discussion, focusing on multiperiod structures, and Paper III speculates about the origin and evolution of the period distribution in the Pleiades.
  ***  

['Rebull L.M.', ' Stauffer J.R.', ' Bouvier J.', ' Cody A.M.', ' Hillenbrand L.A.', ' Soderblom D.R.', ' Valenti J.', ' Barrado D.', ' Bouy H.', ' Ciardi D.', ' Pinsonneault M.', ' Stassun K.', ' Micela G.', ' Aigrain S.', ' Vrba F.', ' Somers G.', ' Gillen E.', ' Collier Cameron A.']
We use K2 to continue the exploration of the distribution of rotation periods in Pleiades that we began in Paper I. We have discovered complicated multiperiod behavior in Pleiades stars using these K2 data, and we have grouped them into categories, which are the focal part of this paper. About 24% of the sample has multiple, real frequencies in the periodogram, sometimes manifesting as obvious beating in the LCs. Those having complex and/or structured periodogram peaks, unresolved multiple periods, and resolved close multiple periods are likely due to spot/spot group evolution and/or latitudinal differential rotation; these largely compose the slowly rotating sequence in P versus (V-K_s_)_0_ identified in Paper I. The fast sequence in P versus (V-K_s_)_0_ is dominated by single-period stars; these are likely to be rotating as solid bodies. Paper III continues the discussion, speculating about the origin and evolution of the period distribution in the Pleiades.
  ***  

['Stauffer J.', ' Rebull L.', ' Bouvier J.', ' Hillenbrand L.A.', ' Collier-Cameron A.', ' Pinsonneault M.', ' Aigrain S.', ' Barrado D.', ' Bouy H.', ' Ciardi D.', ' Cody A.M.', ' David T.', ' Micela G.', ' Soderblom D.', ' Somers G.', ' Stassun K.G.', ' Valenti J.', ' Vrba F.J.']
We use high-quality K2 light curves for hundreds of stars in the Pleiades to better understand the angular momentum evolution and magnetic dynamos of young low-mass stars. The K2 light curves provide not only rotational periods but also detailed information from the shape of the phased light curve that was not available in previous studies. A slowly rotating sequence begins at (V-K_s_)_0_~1.1 (spectral type F5) and ends at (V-K_s_)_0_~3.7 (spectral type K8), with periods rising from ~2 to ~11 days in that interval. A total of 52% of the Pleiades members in that color interval have periods within 30% of a curve defining the slow sequence; the slowly rotating fraction decreases significantly redward of (V-K_s_)_0_=2.6. Nearly all of the slow-sequence stars show light curves that evolve significantly on timescales less than the K2 campaign duration. The majority of the FGK Pleiades members identified as photometric binaries are relatively rapidly rotating, perhaps because binarity inhibits star-disk angular momentum loss mechanisms during pre-main-sequence evolution. The fully convective late M dwarf Pleiades members (5.0<(V-K_s_)_0_<6.0) nearly always show stable light curves, with little spot evolution or evidence of differential rotation. During pre-main-sequence evolution from ~3Myr (NGC2264 age) to ~125Myr (Pleiades age), stars of 0.3M_{Sun}_ shed about half of their angular momentum, with the fractional change in period between 3 and 125Myr being nearly independent of mass for fully convective stars. Our data also suggest that very low mass binaries form with rotation periods more similar to each other and faster than would be true if drawn at random from the parent population of single stars.
  ***  

['Somers G.', ' Stassun K.G.']
Precise measurements of eclipsing binary parameters and statistical studies of young clusters have suggested that some magnetically active low-mass dwarfs possess radii inflated by ~5%-15% relative to theoretical expectations. If true, this effect should be pronounced in young open clusters, due to the rapid rotation and strong magnetic activity of their most extreme members. We explore this possibility by determining empirical radii for 83 members of the nearby Pleiades open cluster, using spectral energy distribution fitting to establish F_bol_ with a typical accuracy of ~3% together with color and spectro-photometric indices to determine T_eff_. We find several Pleiades members with radii inflated above radius-T_eff_ models from state-of-the-art calculations, and apparent dispersions in radii for the K-dwarfs of the cluster. Moreover, we demonstrate that this putative radius inflation correlates strongly with rotation rate, consistent with inflation of young stars by magnetic activity and/or starspots. We argue that this signal is not a consequence of starspot-induced color anomalies, binarity, or depth effects in the cluster, employing Gaia DR1 distances as a check. Finally, we consider the lithium abundances of these stars, demonstrating a triple correlation between rotation rate, radius inflation, and enhanced lithium abundance. Our result-already significant to ~99.99% confidence-provides strong support for a magnetic origin of the inflated radii and lithium dispersion observed in young, low-mass stars.
  ***  

['Jao W.-C.', ' Henry T.J.', ' Winters J.G.', ' Subasavage J.P.', ' Riedel A.R.', ' Silverstein M.L.', ' Ianna P.A.']
Parallaxes, proper motions, and optical photometry are presented for 51 systems consisting of 37 cool subdwarf and 14 additional high proper motion systems. Thirty-seven systems have parallaxes reported for the first time, 15 of which have proper motions of at least 1"/yr. The sample includes 22 newly identified cool subdwarfs within 100 pc, of which three are within 25 pc, and an additional five subdwarfs from 100 to 160 pc. Two systems-LSR 1610-0040 AB and LHS 440 AB-are close binaries exhibiting clear astrometric perturbations that will ultimately provide important masses for cool subdwarfs. We use the accurate parallaxes and proper motions provided here, combined with additional data from our program and others, to determine that effectively all nearby stars with tangential velocities greater than 200 km/s are subdwarfs. We compare a sample of 167 confirmed cool subdwarfs to nearby main sequence dwarfs and Pleiades members on an observational Hertzsprung-Russell diagram using M_V_ versus (V-K_s_) to map trends of age and metallicity. We find that subdwarfs are clearly separated for spectral types K5-M5, indicating that the low metallicities of subdwarfs set them apart in the H-R diagram for (V-K_s_)=3-6. We then apply the tangential velocity cutoff and the subdwarf region of the H-R diagram to stars with parallaxes from Gaia Data Release 1 and the MEarth Project to identify a total of 29 new nearby subdwarf candidates that fall clearly below the main sequence.
  ***  

['Rizzuto A.C.', ' Mann A.W.', ' Vanderburg A.', ' Kraus A.L.', ' Covey K.R.']
Detection of transiting exoplanets around young stars is more difficult than for older systems owing to increased stellar variability. Nine young open cluster planets have been found in the K2 data, but no single analysis pipeline identified all planets. We have developed a transit search pipeline for young stars that uses a transit-shaped notch and quadratic continuum in a 12 or 24 hr window to fit both the stellar variability and the presence of a transit. In addition, for the most rapid rotators (P_rot_<2 days) we model the variability using a linear combination of observed rotations of each star. To maximally exploit our new pipeline, we update the membership for four stellar populations observed by K2 (Upper Scorpius, Pleiades, Hyades, Praesepe) and conduct a uniform search of the members. We identify all known transiting exoplanets in the clusters, 17 eclipsing binaries, one transiting planet candidate orbiting a potential Pleiades member, and three orbiting unlikely members of the young clusters. Limited injection recovery testing on the known planet hosts indicates that for the older Praesepe systems we are sensitive to additional exoplanets as small as 1-2 R_{Earth}_, and for the larger Upper Scorpius planet host (K2-33) our pipeline is sensitive to ~4 R_{Earth}_ transiting planets. The lack of detected multiple systems in the young clusters is consistent with the expected frequency from the original Kepler sample, within our detection limits. With a robust pipeline that detects all known planets in the young clusters, occurrence rate testing at young ages is now possible.
  ***  

['Rebull L.M.', ' Stauffer J.R.', ' Cody A.M.', ' Hillenbrand L.A.', ' David T.J.', ' Pinsonneault M.']
We present an analysis of K2 light curves (LCs) for candidate members of the young Upper Sco (USco) association (~8 Myr) and the neighboring {rho} Oph embedded cluster (~1 Myr). We establish ~1300 stars as probable members, ~80% of which are periodic. The phased LCs have a variety of shapes which can be attributed to physical causes ranging from stellar pulsation and stellar rotation to disk-related phenomena. We identify and discuss a number of observed behaviors. The periods are ~0.2-30 days with a peak near 2 days and the rapid period end nearing breakup velocity. M stars in the young USco region rotate systematically faster than GK stars, a pattern also present in K2 data for the older Pleiades and Praesepe systems. At higher masses (types FGK), the well-defined period-color relationship for slowly rotating stars seen in the Pleiades and Praesepe systems is not yet present in USco. Circumstellar disks are present predominantly among the more slowly rotating M stars in USco, with few disks in the subday rotators. However, M dwarfs with disks rotate faster on average than FGK systems with disks. For four of these disked M dwarfs, we provide direct evidence for disk locking based on the K2 LC morphologies. Our preliminary analysis shows a relatively mass-independent spin-up by a factor of ~3.5 between USco and the Pleiades, then mass-dependent spin-down between Pleiades and Praesepe.
  ***  

['Hillenbrand L.A.', ' Zhang C.', ' Riddle R.L.', ' Baranec C.', ' Ziegler C.', ' Law N.M.', ' Stauffer J.']
We identify and roughly characterize 66 candidate binary star systems in the Pleiades, Praesepe, and NGC 2264 star clusters, based on robotic adaptive optics imaging data obtained using Robo-AO at the Palomar 60" telescope. Only ~10% of our imaged pairs were previously known. We detect companions at red optical wavelengths, with physical separations ranging from a few tens to a few thousands of au. A three-sigma contrast curve generated for each final image provides upper limits to the brightness ratios for any undetected putative companions. The observations are sensitive to companions with a maximum contrast of ~6^m^ at larger separations. At smaller separations, the mean (best) raw contrast at 2" is 3.8^m^ (6^m^), at 1" is 3.0^m^ (4.5^m^), and at 0.5" is 1.9^m^ (3^m^). Point-spread function subtraction can recover nearly the full contrast in the closer separations. For detected candidate binary pairs, we report separations, position angles, and relative magnitudes. Theoretical isochrones appropriate to the Pleiades and Praesepe clusters are then used to determine the corresponding binary mass ratios, which range from 0.2 to 0.9 in q=m_2_/m_1_. For our sample of roughly solar-mass (FGK type) stars in NGC 2264 and sub-solar-mass (K and early M-type) primaries in the Pleiades and Praesepe, the overall binary frequency is measured at ~15.5%+/-2%. However, this value should be considered a lower limit to the true binary fraction within the specified separation and mass ratio ranges in these clusters, given that complex and uncertain corrections for sensitivity and completeness have not been applied.
  ***  

['Anthony-Twarog B.J.', ' Deliyannis C.P.', ' Harmer D.', ' Lee-Brown D.B.', ' Steinhauer A.', ' Sun Q.', ' Twarog B.A.']
Hydra spectra of 85 G-K dwarfs in the young cluster M35 near the Li 6708 {AA} line region are analyzed. From velocities and Gaia astrometry, 78 are likely single-star members that, combined with previous work, produce 108 members with T_eff_ ranging from 6150 to 4000 K as defined by multicolor, broadband photometry, E(B-V)=0.20, and [Fe/H]=-0.15, though there are indications the metallicity may be closer to solar. The Lithium abundance A(Li) follows a well-delineated decline from 3.15 for the hottest stars to upper limits =<1.0 among the coolest dwarfs. Contrary to earlier work, M35 includes single stars at systematically higher A(Li) than the mean cluster relation. This subset exhibits higher V_ROT_ than the more Li-depleted sample and, from photometric rotation periods, is dominated by stars classed as convective (C); all others are interface (I) stars. The cool, high-Li rapid rotators (RRs) are consistent with models that simultaneously consider rapid rotation and radius inflation; RRs hotter than the Sun exhibit excess Li depletion, as predicted by the models. The A(Li) distribution with color and rotation period, when compared to the Hyades/Praesepe and the Pleiades, is consistent with gyrochronological analysis placing M35's age between the older M34 and younger Pleiades. However, the Pleiades display a more excessive range in A(Li) and rotation period than M35 on the low-Li, slow-rotation side of the distribution, with supposedly younger stars at a given T_eff_ in the Pleiades spinning slower, with A(Li) reduced by more than a factor of four compared to M35.
  ***  

['Curtis J.L.', ' Agueros M.A.', ' Mamajek E.E.', ' Wright J.T.', ' Cummings J.D.']
Pisces-Eridanus (Psc-Eri), a nearby (d~80-226 pc) stellar stream stretching across ~120{deg} of the sky, was recently discovered with Gaia data. The stream was claimed to be ~1 Gyr old, which would make it an exceptional discovery for stellar astrophysics, as star clusters of that age are rare and tend to be distant, limiting their utility as benchmark samples. We test this old age for Psc-Eri in two ways. First, we compare the rotation periods for 101 low-mass members (measured using time-series photometry from the Transiting Exoplanet Survey Satellite) to those of well-studied open clusters. Second, we identify 34 new high-mass candidate members, including the notable stars {lambda} Tauri (an Algol-type eclipsing binary) and HD 1160 (host to a directly imaged object near the hydrogen-burning limit). We conduct an isochronal analysis of the color-magnitude data for these highest-mass members, again comparing our results to those for open clusters. Both analyses show that the stream has an age consistent with that of the Pleiades, i.e., ~120 Myr. This makes the Psc-Eri stream an exciting source of young benchmarkable stars and, potentially, exoplanets located in a more diffuse environment that is distinct from that of the Pleiades and of other dense star clusters.
  ***  

['Rebull L.M.', ' Stauffer J.R.', ' Cody A.M.', ' Hillenbrand L.A.', ' Bouvier J.', ' Roggero N.', ' David T.J.']
We present an analysis of K2 light curves (LCs) from Campaigns 4 and 13 for members of the young (~3Myr) Taurus association, in addition to an older (~30Myr) population of stars that is largely in the foreground of the Taurus molecular clouds. Out of 156 of the highest-confidence Taurus members, we find that 81% are periodic. Our sample of young foreground stars is biased and incomplete, but nearly all stars (37/38) are periodic. The overall distribution of rotation rates as a function of color (a proxy for mass) is similar to that found in other clusters: the slowest rotators are among the early M spectral types, with faster rotation toward both earlier FGK and later M types. The relationship between period and color/mass exhibited by older clusters such as the Pleiades is already in place by Taurus age. The foreground population has very few stars but is consistent with the USco and Pleiades period distributions. As found in other young clusters, stars with disks rotate on average slower, and few with disks are found rotating faster than ~2days. The overall amplitude of the LCs decreases with age, and higher-mass stars have generally lower amplitudes than lower-mass stars. Stars with disks have on average larger amplitudes than stars without disks, though the physical mechanisms driving the variability and the resulting LC morphologies are also different between these two classes.
  ***  

['Micela G.', ' Sciortino S.', ' Vaiana G.S.', ' Harnden F.R.', ' Rosner R.', ' Schmitt J.H.M.M.']
Coronal X-ray emission of the Pleiades stars is investigated, and maximum likelihood, integral X-ray luminosity functions are computed for Pleiades members in selected color-index ranges. A detailed search is conducted for long-term variability in the X-ray emission of those stars observed more than once. An overall comparison of the survey results with those of previous surveys confirms the ubiquity of X-ray emission in the Pleiades cluster stars and its higher rate of emission with respect to older stars. It is found that the X-ray emission from dA and early dF stars cannot be proven to be dissimilar to that of Hyades and field stars of the same spectral type. The Pleiades cluster members show a real rise of the X-ray luminosity from dA stars to early dF stars. X-ray emission for the young, solar-like Pleiades stars is about two orders of magnitude more intense than for the nearby solar-like stars.
  ***  

['Najita J.R.', ' Tiede G.P.', ' Carr J.S.']
We investigate the low-mass population of the young cluster IC 348 down to the deuterium-burning limit, a fiducial boundary between brown dwarf and planetary mass objects, using a new and innovative method for the spectral classification of late-type objects. Using photometric indices, constructed from HST/NICMOS narrowband imaging, that measure the strength of the 1.9{mu}m water band, we determine the spectral type and reddening for every M-type star in the field, thereby separating cluster members from the interloper population. Due to the efficiency of our spectral classification technique, our study is complete from ~0.7 to 0.015M_{sun}_. The mass function derived for the cluster in this interval, dN/dlogM{prop.to}M^0.5^, is similar to that obtained for the Pleiades, but appears significantly more abundant in brown dwarfs than the mass function for companions to nearby Sunlike stars. This provides compelling observational evidence for different formation and evolutionary histories for substellar objects formed in isolation versus as companions. Because our determination of the IMF is complete to very low masses, we can place interesting constraints on the role of physical processes such as fragmentation in the star and planet formation process and the fraction of dark matter in the Galactic halo that resides in substellar objects.
  ***  

['Meibom S.', ' Mathieu R.D.', ' Stassun K.G.']
We present the results of a five month photometric time-series survey for stellar rotation over a 40'x40' field centered on the 150Myr open cluster M35 (=NGC 2168). We report rotation periods for 441 stars within this field and determine their cluster membership and binarity based on a decade-long radial velocity survey, proper-motion measurements, and multiband photometric observations. We find that 310 of the stars with measured rotation periods are late-type members of M35. The distribution of rotation periods for cluster members span more than 2 orders of magnitude from ~0.1 to 15 days, not constrained by the sampling frequency and the timespan of the survey. With an age between the zero-age main sequence and the Hyades, and with ~6 times more rotation periods than measured in the Pleiades, M35 permit detailed studies of early rotational evolution of late-type stars. Nearly 80% of the 310 rotators lie on two distinct sequences in the color-period plane, and define clear relations between stellar rotation period and color (mass). The M35 color-period diagram enables us to determine timescales for the transition between the two rotational states, of ~60Myr and ~140Myr for G and K dwarfs, respectively.
  ***  

['Cottaar M.', ' Covey K.R.', ' Meyer M.R.', ' Nidever D.L.', ' Stassun K.G.', ' Foster J.B.', ' Tan J.C.', ' Chojnowski S.D.', ' da Rio N.', ' Flaherty K.M.', ' Frinchaboy P.M.', ' Skrutskie M.', ' Majewski S.R.', ' Wilson J.C.', ' Zasowski G.']
Over two years, 8859 high-resolution H-band spectra of 3493 young (1-10Myr) stars were gathered by the multi-object spectrograph of the APOGEE project as part of the IN-SYNC ancillary program of the SDSS-III survey. Here we present the forward modeling approach used to derive effective temperatures, surface gravities, radial velocities, rotational velocities, and H-band veiling from these near-infrared spectra. We discuss in detail the statistical and systematic uncertainties in these stellar parameters. In addition, we present accurate extinctions by measuring the E(J-H) of these young stars with respect to the single-star photometric locus in the Pleiades. Finally, we identify an intrinsic stellar radius spread of about 25% for late-type stars in IC 348 using three (nearly) independent measures of stellar radius, namely, the extinction-corrected J-band magnitude, the surface gravity, and the Rsini from the rotational velocities and literature rotation periods. We exclude that this spread is caused by uncertainties in the stellar parameters by showing that the three estimators of stellar radius are correlated, so that brighter stars tend to have lower surface gravities and larger Rsini than fainter stars at the same effective temperature.
  ***  

['Meng H.Y.A.', ' Su K.Y.L.', ' Rieke G.H.', ' Rujopakarn W.', ' Myers G.', ' Cook M.', ' Erdelyi E.', ' Maloney C.', ' McMath J.', ' Persha G.', ' Poshyachinda S.', ' Reichart D.E.']
Luminous debris disks of warm dust in the terrestrial planet zones around solar-like stars were recently found to vary, which is indicative of ongoing large-scale collisions of rocky objects. We use Spitzer 3.6 and 4.5um time-series observations in 2012 and 2013 (extended to 2014 in one case) to monitor five more debris disks with unusually high fractional luminosities ("extreme debris disk"), including P1121 in the open cluster M47 (80 Myr), HD15407A in the AB Dor moving group (80Myr), HD 23514 in the Pleiades (120Myr), HD145263 in the Upper Sco Association (10Myr), and the field star BD+20 307 (>~1Gyr). Together with the published results for ID8 in NGC2547 (35Myr), this makes the first systematic time-domain investigation of planetary impacts outside the solar system. Significant variations with timescales shorter than a year are detected in five out of the six extreme debris disks we monitored. However, different systems show diverse sets of characteristics in the time domain, including long-term decay or growth, disk temperature variations, and possible periodicity.
  ***  

['Covey K.R.', ' Agueros M.A.', ' Law N.M.', ' Liu J.', ' Ahmadi A.', ' Laher R.', ' Levitan D.', ' Sesar B.', ' Surace J.']
Stellar rotation periods (P_rot_) measured in open clusters have proved to be extremely useful for studying stars' angular momentum content and rotationally driven magnetic activity, which are both age- and mass-dependent processes. While P_rot_ measurements have been obtained for hundreds of solar-mass members of the Pleiades, measurements exist for only a few low-mass (<0.5 M_{sun}_) members of this key laboratory for stellar evolution theory. To fill this gap, we report P_rot_ for 132 low-mass Pleiades members (including nearly 100 with M=<0.45 M_{sun}_), measured from photometric monitoring of the cluster conducted by the Palomar Transient Factory in late 2011 and early 2012. These periods extend the portrait of stellar rotation at 125 Myr to the lowest-mass stars and re-establish the Pleiades as a key benchmark for models of the transport and evolution of stellar angular momentum. Combining our new P_rot_ with precise BVIJHK photometry reported by Stauffer et al. (2007, J/ApJS/172/663) and Kamai et al. (2014, J/AJ/148/30), we investigate known anomalies in the photometric properties of K and M Pleiades members. We confirm the correlation detected by Kamai et al. between a star's P_rot_ and position relative to the main sequence in the cluster's color-magnitude diagram. We find that rapid rotators have redder (V-K) colors than slower rotators at the same V, indicating that rapid and slow rotators have different binary frequencies and/or photospheric properties. We find no difference in the photometric amplitudes of rapid and slow rotators, indicating that asymmetries in the longitudinal distribution of starspots do not scale grossly with rotation rate.
  ***  

['Rebull L.M.', ' Stauffer J.R.', ' Hillenbrand L.A.', ' Cody A.M.', ' Bouvier J.', ' Soderblom D.R.', ' Pinsonneault M.', ' Hebb L.']
We have Fourier-analyzed 941 K2 light curves (LCs) of likely members of Praesepe, measuring periods for 86% and increasing the number of rotation periods (P) by nearly a factor of four. The distribution of P versus (V-Ks), a mass proxy, has three different regimes: (V-Ks)<1.3, where the rotation rate rapidly slows as mass decreases; 1.3<(V-Ks)<4.5, where the rotation rate slows more gradually as mass decreases; and (V-Ks)>4.5, where the rotation rate rapidly increases as mass decreases. In this last regime, there is a bimodal distribution of periods, with few between ~2 and ~10 days. We interpret this to mean that once M stars start to slow down, they do so rapidly. The K2 period-color distribution in Praesepe (~790Myr) is much different than that in the Pleiades (~125Myr) for late F, G, K, and early-M stars; the overall distribution moves to longer periods and is better described by two line segments. For mid-M stars, the relationship has a similarly broad scatter and is steeper in Praesepe. The diversity of LCs and of periodogram types is similar in the two clusters; about a quarter of the periodic stars in both clusters have multiple significant periods. Multi- periodic stars dominate among the higher masses, starting at a bluer color in Praesepe ((V-Ks)~1.5) than in the Pleiades ((V-Ks)~2.6). In Praesepe, there are relatively more LCs that have two widely separated periods, {Delta}P>6days. Some of these could be examples of M star binaries where one star has spun down but the other has not.
  ***  

['Zhang Z.', ' Liu M.C.', ' Best W.M.J.', ' Magnier E.A.', ' Aller K.M.', ' Chambers K.C.', ' Draper P.W.', ' Flewelling H.', ' Hodapp K.W.', ' Kaiser N.', ' Kudritzki R.-P.', ' Metcalfe N.', ' Wainscoat R.J.', ' Waters C.']
We are conducting a proper-motion survey for young brown dwarfs in the Taurus-Auriga molecular cloud based on the Pan-STARRS1 3{pi} Survey. Our search uses multi-band photometry and astrometry to select candidates, and is wider (370deg^2^) and deeper (down to ~3M_Jup_) than previous searches. We present here our search methods and spectroscopic follow-up of our high-priority candidates. Since extinction complicates spectral classification, we have developed a new approach using low-resolution (R~100) near-infrared spectra to quantify reddening-free spectral types, extinctions, and gravity classifications for mid-M to late-L ultracool dwarfs (<=100-3M_Jup_ in Taurus). We have discovered 25 low-gravity (VL-G) and the first 11 intermediate-gravity (INT-G) substellar (M6-L1) members of Taurus, constituting the largest single increase of Taurus brown dwarfs to date. We have also discovered 1 new Pleiades member and 13 new members of the Perseus OB2 association, including a candidate very wide separation (58kau) binary. We homogeneously reclassify the spectral types and extinctions of all previously known Taurus brown dwarfs. Altogether our discoveries have thus far increased the substellar census in Taurus by ~40% and added three more L-type members (<~5-10M_Jup_). Most notably, our discoveries reveal an older (>10Myr) low-mass population in Taurus, in accord with recent studies of the higher-mass stellar members. The mass function appears to differ between the younger and older Taurus populations, possibly due to incompleteness of the older stellar members or different star formation processes.
  ***  

['Torres G.']
Radial velocities for the early-type stars in the Pleiades cluster have always been challenging to measure because of the significant rotational broadening of the spectral lines. The large scatter in published velocities has led to claims that many are spectroscopic binaries, and in several cases, preliminary orbital solutions have been proposed. To investigate these claims, we obtained and report here velocity measurements for 33 rapidly rotating B, A, and early F stars in the Pleiades region, improving significantly on the precision of the historical velocities for most objects. With one or two exceptions, we do not confirm any of the previous claims of variability, and we also rule out all four of the previously published orbital solutions, for HD 22637, HD 23302, HD 23338, and HD 23410. We do find HD 22637 to be a binary but with a different period (71.8d). HD 23338 is likely a binary as well, with a preliminary 8.7yr period also different from the one published. Additionally, we report a 3635d orbit for HD 24899, another new spectroscopic binary in the cluster. From the 32 bona fide members in our sample, we determine a mean radial velocity for the Pleiades of 5.79+/-0.24km/s, or 5.52+/-0.31km/s when objects with known visual companions are excluded. Adding these astrometric binaries to the new spectroscopic ones, we find a lower limit to the binary fraction among the B and A stars of 37%. In addition to the velocities, we measure vsini for all stars, ranging between 69 and 317km/s.
  ***  

['Gagne J.', ' David T.J.', ' Mamajek E.E.', ' Mann A.W.', ' Faherty J.K.', ' Bedard A.']
We present an analysis of the newly identified {mu}Tau Association (MUTA) of young stars at ~150pc from the Sun that is part of the large Cas-Tau structure, coeval and comoving with the {alpha}Persei cluster. This association is also located in the vicinity of the Taurus-Auriga star-forming region and the Pleiades association, although it is unrelated to them. We identify more than 500 candidate members of MUTA using Gaia DR2 data and the BANYAN {Sigma} tool, and we determine an age of 62{+/-}7Myr for its population based on an empirical comparison of its color-magnitude diagram sequence with those of other nearby young associations. The MUTA association is related to the Theia 160 group of Kounkel & Covey and corresponds to the e Tau group of Liu et al. It is also part of the Cas-Tau group of Blaauw. As part of this analysis, we introduce an iterative method based on spectral templates to perform an accurate correction of interstellar extinction of Gaia DR2 photometry, needed because of its wide photometric bandpasses. We show that the members of MUTA display an expected increased rate of stellar activity and faster rotation rates compared with older stars, and that literature measurements of the lithium equivalent width of nine G0- to K3-type members are consistent with our age determination. We show that the present- day mass function of MUTA is consistent with other known nearby young associations. We identify WD0340+103 as a hot, massive white dwarf remnant of a B2 member that left its planetary nebula phase only 270000yr ago, posing an independent age constraint of 60_-6_^+8^ Myr for MUTA, consistent with our isochrone age. This relatively large collection of comoving young stars near the Sun indicates that more work is required to unveil the full kinematic structure of the complex of young stars surrounding {alpha} Persei and Cas-Tau.
  ***  

['Brown T.M.', ' Garcia R.A.', ' Mathur S.', ' Metcalfe T.S.', ' Santos A.R.G.']
We analyze space-based time-series photometry of Sun-like stars, mostly in the Pleiades, but also field stars and the Sun itself. We focus on timescales between roughly 1hr and 1day. In the corresponding frequency band these stars display brightness fluctuations with a decreasing power-law continuous spectrum. K2 and Kepler observations show that the rms flicker due to this mid-frequency continuum (MFC) can reach almost 1%, approaching the modulation amplitude from active regions. The MFC amplitude varies by a factor up to 40 among Pleiades members with similar Teff, depending mainly on the stellar Rossby number Ro. For Ro<=0.04, the mean amplitude is roughly constant at about 0.4%; at larger Ro the amplitude decreases rapidly, shrinking by about two orders of magnitude for Ro~1. Among stars, the MFC amplitude correlates poorly with that of modulation from rotating active regions. Among field stars observed for 3yr by Kepler, the quarterly average modulation amplitudes from active regions are much more time variable than the quarterly MFC amplitudes. We argue that the process causing the MFC is largely magnetic in nature and that its power-law spectrum comes from magnetic processes distinct from the star's global dynamo, with shorter timescales. By analogy with solar phenomena, we hypothesize that the MFC arises from a (sometimes energetic) variant of the solar magnetic network, perhaps combined with rotation-related changes in the morphology of supergranules.
  ***  

['Torres G.', ' Latham D.W.', ' Quinn S.N.']
We present the results of a spectroscopic monitoring program of the Pleiades region aimed at completing the census of spectroscopic binaries in the cluster, extending it to longer periods than previously reachable. We gathered 6104 spectra of 377 stars between 1981 and 2021, and merged our radial velocities with 1151 measurements from an independent survey by others started three years earlier. With the combined data spanning more than 43yr, we have determined orbits for some 30 new binary and multiple systems, more than doubling the number previously known in the Pleiades. The longest period is 36.5yr. A dozen additional objects display long-term trends in their velocities, implying even longer periods. We examine the collection of orbital elements for cluster members, and find that the shape of the incompleteness-corrected distribution of periods (up to 104 days) is similar to that of solar-type binaries in the field, while that of the eccentricities is different. The mass-ratio distribution is consistent with being flat. The binary frequency in the Pleiades for periods up to 104 days is 25%+/-3% after corrections for undetected binaries, which is nearly double that of the field up to the same period. The total binary frequency including known astrometric binaries is at least 57%. We estimate the internal radial velocity dispersion in the cluster to be 0.48+/-0.04km/s. We revisit the determination of the tidal circularization period, and confirm its value to be 7.2+/-1.0d, with an improved precision compared to an earlier estimate.
  ***  

['Heyl J.', ' Caiazzo I.', ' Richer H.B.']
We search through an eight million cubic parsec volume surrounding the Pleiades star cluster and the Sun to identify both the current and past members of the Pleiades cluster within the Gaia EDR3 data set. We find nearly 1300 current cluster members and 289 former cluster candidates. Many of these candidates lie well in front of or behind the cluster from our point of view, so formerly they were considered cluster members, but their parallaxes put them more than 10pc from the center of the cluster today. Over the past 100Myr we estimate that the cluster has lost twenty percent of its mass including two massive white dwarf stars and the {alpha}^2^ Canum Venaticorum type variable star, 41 Tau. All three white dwarfs associated with the cluster are massive (1.01-1.06M _{sun}_) and have progenitors with main-sequence masses of about six solar masses. Although we did not associate any giant stars with the cluster, the cooling time of the oldest white dwarf of 60Myr gives a firm lower limit on the age of the cluster.
  ***  

['Micela G.', ' Sciortino S.', ' Kashyap V.', ' Harnden F.R.', ' Rosner R.']
Of 214 stars in the core of the Pleiades, 99 were detected in X-rays with the ROSAT PSPC. This catalog lists the characteristics of the stars taken from the literature, in table1.dat and the rotational and X-ray characteristics in table5.dat.
  ***  

['Stauffer J.R.', ' Hartmann L.W.', ' Fazio G.G.', ' Allen L.E.', ' Patten B.M.', ' Lowrance P.J.', ' Hurt R.L.', ' Rebull L.M.', ' Cutri R.M.', ' Ramirez S.V.', ' Young E.T.', ' Rieke G.H.', ' Gorlova N.I.', ' Muzerolle J.C.', ' Slesnick C.L.', ' Skrutskie M.F.']
We make use of new near- and mid-IR photometry of the Pleiades cluster in order to help identify proposed cluster members. We also use the new photometry with previously published photometry to define the single-star main-sequence locus at the age of the Pleiades in a variety of color-magnitude planes. The new near- and mid-IR photometry extend effectively 2 mag deeper than the 2MASS All-Sky Point Source catalog, and hence allow us to select a new set of candidate very low-mass and substellar mass members of the Pleiades in the central square degree of the cluster. We identify 42 new candidate members fainter than K_s_=14 (corresponding to 0.1M_{sun}_). These candidate members should eventually allow a better estimate of the cluster mass function to be made down to of order 0.04M_{sun}_. We also use new IRAC data, in particular the images obtained at 8um, in order to comment briefly on interstellar dust in and near the Pleiades.
  ***  

['Kim B.', ' An D.', ' Stauffer J.R.', ' Lee Y.S.', ' Terndrup D.M.', ' Johnson J.A.']
The tension between the Hipparcos parallax of the Pleiades and other independent distance estimates continues even after the new reduction of the Hipparcos astrometric data and the development of a new geometric distance measurement for the cluster. A short Pleiades distance from the Hipparcos parallax predicts a number of stars in the solar neighborhood that are sub-luminous at a given photospheric abundance. We test this hypothesis using the spectroscopic abundances for a subset of stars in the Hipparcos catalog, which occupy the same region as the Pleiades in the color-magnitude diagram. We derive stellar parameters for 170 nearby G- and K-type field dwarfs in the Hipparcos catalog based on high-resolution spectra obtained using KPNO 4m echelle spectrograph. Our analysis shows that, when the Hipparcos parallaxes are adopted, most of our sample stars follow empirical color-magnitude relations. A small fraction of stars are too faint compared to main-sequence fitting relations by {Delta}M_V_>~0.3mag, but the differences are marginal at a 2{sigma} level, partly due to relatively large parallax errors. On the other hand, we find that the photometric distances of stars showing signatures of youth as determined from lithium absorption line strengths and R'_HK_ chromospheric activity indices are consistent with the Hipparcos parallaxes. Our result is contradictory to a suggestion that the Pleiades distance from main-sequence fitting is significantly altered by stellar activity and/or the young age of its stars, and provides an additional supporting evidence for the long-distance scale of the Pleiades.
  ***  

['Walker A.R.', ' Laney C.D.']
A colour magnitude diagram to V=20 is given for 395 stars in the heavily reddened open cluster NGC 6649. The absorption-corrected distance modulus is 11.00+/-0.15mag (1585+/-110pc) assuming R(OB)=3.27+/-0.10 for NGC 6649 and based on a ZAMS with zero point referenced to a Pleiades distance modulus of 5.56mag. The range of reddening over the 5arcmin diameter of the cluster is {DELTA}E(B-V)=0.3mag. NGC 6649 contains the double mode Cepheid V367 Sct, which has <M_V_>=-3.80+/-0.06 and <B_0_>-<V_0_>=0.58+/-0.02.
  ***  

['Pinfield D.J.', ' Hodgkin S.T.', ' Jameson R.F.', ' Cossburn M.R.', ' Hambly N.C.', ' Devereux N.']
We present the results of a six-square-degree Pleiades survey in I and Z, which is photometrically complete to approximately I_KP_=19.2mag (I_C_=19.6 in the Pleiades). We remove non-cluster contamination on the basis of proper motions and infrared photometry, and present 339 candidate cluster members, 30 of which are fainter than I_KP_=17.5, and are thus strong brown-dwarf candidates.
  ***  

['Naylor T.', ' Totten E.J.', ' Jeffries R.D.', ' Pozzo M.', ' Devey C.R.', ' Thompson S.A.']
We have developed the techniques required to use Naylor's optimal photometry algorithm of to create colour-magnitude diagrams with well-defined completeness functions. To achieve this we first demonstrate that the optimal extraction is insensitive to uncertainties in the measured position of the star. We then show how to correct the optimally extracted fluxes such that they correspond to those measured in a large aperture, so aperture photometry of standard stars can be used to place the measurements on a standard system. The technique simultaneously removes the effects of a position-dependent point spread function. Finally, we develop a method called 'ghosting', which calculates the completeness corrections in the absence of an accurate description of the point spread function. We apply these techniques to the young cluster NGC 2547 (=C0809-491), and use an X-ray-selected sample to find an age of 20-35Myr and an intrinsic distance modulus of 8.00-8.15mag. We use these isochrones to select members from our photometric surveys. Our derived luminosity function shows a well-defined Wielen dip, making NGC 2547 the youngest cluster in which such a feature has been observed. Our derived mass function spans the range 0.1-6M_{sun}_ and is similar to that for the field and the older, more massive clusters M35 and the Pleiades, supporting the idea of a universal initial mass function.
  ***  

['Pinfield D.J.', ' Dobbie P.D.', ' Jameson R.F.', ' Steele I.A.', ' Jones H.R.A.', ' Katsiyannis A.C.']
We present near-infrared J-, H- and K-band photometry and optical spectroscopy of low-mass star and brown dwarf (BD) candidates in the Pleiades and Praesepe open clusters. We flag non-members from their position in K, I-K and J, J-K colour-magnitude diagrams (CMDs), and J-H, H-K two-colour diagrams.
  ***  

['Hartman J.D.', ' Bakos G.A.', ' Kovacs G.', ' Noyes R.W.']
Using data from the Hungarian-made Automated Telescope Network (HATNet) survey for transiting exoplanets, we measure photometric rotation periods for 368 Pleiades stars with 0.4~<M~<1.3M_{sun}_. We detect periodic variability for 74 per cent of the cluster members in this mass range that are within our field-of-view, and 93 per cent of the members with 0.7~<M~<1.0M_{sun}_. This increases, by a factor of 5, the number of Pleiades members with measured periods. We compare these data to the rich sample of spectroscopically determined projected equatorial rotation velocities (vsini) available in the literature for this cluster. Included in our sample are 14 newly identified probable cluster members which have proper motions, photometry and rotation periods consistent with membership.
  ***  

['Lodieu N.', ' Deacon N.R.', ' Hambly N.C.']
We present the results of a deep wide-field near-infrared survey of the entire Pleiades cluster recently released as part of the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Clusters Survey (GCS) Data Release 9 (DR9). We have identified a sample of ~1000 Pleiades cluster member candidates combining photometry in five near-infrared passbands and proper motions derived from the multiple epochs provided by the UKIDSS GCS DR9. We also provide revised membership for all previously published Pleiades low-mass stars and brown dwarfs in the past decade recovered in the UKIDSS GCS DR9 Pleiades survey based on the new photometry and astrometry provided by the GCS.
  ***  

['Bell C.P.M.', ' Naylor T.', ' Mayne N.J.', ' Jeffries R.D.', ' Littlefair S.P.']
We present a critical assessment of commonly used pre-main-sequence isochrones by comparing their predictions to a set of well-calibrated colour-magnitude diagrams of the Pleiades in the wavelength range 0.4-2.5um. Our analysis shows that for temperatures less than 4000K, the models systematically overestimate the flux by a factor of 2 at 0.5um, though this decreases with wavelength, becoming negligible at 2.2um. In optical colours this will result in the ages for stars younger than 10Myr being underestimated by factors of between 2 and 3. We show that using observations of standard stars to transform the data into a standard system can introduce significant errors in the positioning of pre-main sequences in colour-magnitude diagrams. Therefore, we have compared the models to the data in the natural photometric system in which the observations were taken. Thus we have constructed and tested a model of the system responses for the Wide-Field Camera on the Isaac Newton Telescope. As a benchmark test for the development of pre-main-sequence models, we provide both our system responses and the Pleiades sequence.
  ***  

['Jackson R.J.', ' Deliyannis C.P.', ' Jeffries R.D.']
Rotation periods obtained with the Kepler satellite have been combined with precise measurements of projected rotation velocity from the WIYN 3.5-m telescope to determine the distribution of projected radii for several hundred low-mass (0.1<=M/M_{sun}_<=0.8), fast-rotating members of the Pleiades cluster. A maximum likelihood modelling technique, that takes account of observational uncertainties, selection effects and censored data, and considers the effects of differential rotation and unresolved binarity, has been used to find that the average radius of these stars is 14+/-2 per cent larger at a given luminosity than predicted by current evolutionary models of Dotter et al. and Baraffe et al. The same models are a reasonable match to the interferometric radii of older, magnetically inactive field M dwarfs, suggesting that the over-radius may be associated with the young, magnetically active nature of the Pleiades objects. No evidence is found for any change in this over-radius above and below the boundary marking the transition to full convection. Published evolutionary models that incorporate either the effects of magnetic inhibition of convection or the blocking of flux by dark star-spots do not individually explain the radius inflation, but a combination of the two effects might. The distribution of projected radii is consistent with the adopted hypothesis of a random spatial orientation of spin axes; strong alignments of the spin vectors into cones with an opening semi-angle <30{deg} can be ruled out. Any plausible but weaker alignment would increase the inferred over-radius.
  ***  

['Jackson R.J.', ' Jeffries R.D.', ' Deliyannis C.P.', ' Sun Q.', ' Douglas S.T.']
Rotation periods from Kepler K2 are combined with projected rotation velocities from the WIYN 3.5m telescope to determine projected radii for fast-rotating, low-mass (0.1<=M/M_{sun}_<=0.6) members of the Praesepe cluster. A maximum likelihood analysis that accounts for observational uncertainties, binarity, and censored data yields marginal evidence for radius inflation - the average radius of these stars is 6+/-4 per cent larger at a given luminosity than predicted by commonly used evolutionary models. This overradius is smaller (at 2{sigma} confidence) than was found for similar stars in the younger Pleiades using a similar analysis; any decline appears due to changes occurring in higher mass (>0.25M_{sun}_) stars. Models incorporating magnetic inhibition of convection predict an overradius, but do not reproduce this mass dependence unless superequipartition surface magnetic fields are present at lower masses. Models incorporating flux blocking by starspots can explain the mass dependence but there is no evidence that spot coverage diminishes between the Pleiades and Praesepe samples to accompany the decline in overradius. The fastest rotating stars in both Praesepe and the Pleiades are significantly smaller than the slowest rotators for which a projected radius can be measured. This may be a selection effect caused by more efficient angular momentum loss in larger stars leading to their progressive exclusion from the analysed samples. Our analyses assume random spin-axis orientations; any alignment in Praesepe, as suggested by Kovacs, is strongly disfavoured by the broad distribution of projected radii.
  ***  

['Gillen E.', ' Briegal J.T.', ' Hodgkin S.T.', ' Foreman-Mackey D.', ' Van Leeuwen F.', ' Jackman J.A.G.', ' McCormac J.', ' West R.G.', ' Queloz D.', ' Bayliss D.', ' Goad M.R.', ' Watson C.A.', ' Wheatley P.J.', ' Belardi C.', ' Burleigh M.R.', ' Casewell S.L.', ' Jenkins J.S.', ' Raynard L.', ' Smith A.M.S.', ' Tilbrook R.H.', ' Vines J.I.']
We determine rotation periods for 127 stars in the ~115-Myr-old Blanco 1 open cluster using ~200d of photometric monitoring with the Next Generation Transit Survey. These stars span F5-M3 spectral types (1.2M_{sun}_>~M>~0.3M_{sun}_) and increase the number of known rotation periods in Blanco 1 by a factor of four. We determine rotation periods using three methods: Gaussian process (GP) regression, generalized autocorrelation function (G-ACF), and Lomb-Scargle (LS) periodogram, and find that the GP and G-ACF methods are more applicable to evolving spot modulation patterns. Between mid-F and mid-K spectral types, single stars follow a well-defined rotation sequence from ~2 to 10d, whereas stars in photometric multiple systems typically rotate faster. This may suggest that the presence of a moderate-to-high mass ratio companion inhibits angular momentum loss mechanisms during the early pre-main sequence, and this signature has not been erased at ~100Myr. The majority of mid-F to mid-K stars display evolving modulation patterns, whereas most M stars show stable modulation signals. This morphological change coincides with the shift from a well-defined rotation sequence (mid-F to mid-K stars) to a broad rotation period distribution (late-K and M stars). Finally, we compare our rotation results for Blanco 1 to the similarly aged Pleiades: the single-star populations in both clusters possess consistent rotation period distributions, which suggests that the angular momentum evolution of stars follows a well-defined pathway that is, at least for mid-F to mid-K stars, strongly imprinted by ~100Myr.
  ***  

['Makarov V.V.']
Accurate parallaxes from Gaia DR1 (TGAS) are combined with GALEX visual Nuv magnitudes to produce absolute MNUV magnitudes and an ultraviolet HR diagram for a large sample of astrometric stars. A functional fit is derived of the lower envelope main sequence of the nearest 1403 stars (distance <40pc), which should be reddening-free. Using this empirical fit, 50 nearby stars are selected with significant Nuv excess. These are predominantly late K and early M dwarfs, often associated with X-ray sources, and showing other manifestations of magnetic activity. The sample may include systems with hidden white dwarfs, stars younger than the Pleiades, or, most likely, tight interacting binaries of the BY Dra-type. A separate collection of 40 stars with precise trigonometric parallaxes and Nuv-G colors bluer than 2mag is presented. It includes several known novae, white dwarfs, and binaries with hot subdwarf (sdOB) components, but most remain unexplored.
  ***  

['Bohigas J.']
Selecting the best quality data, I find that nearly all 0.5 to 1.2M_{sun}_ main sequence stars converge to a single rotational mass dependent sequence after 750Myr; when the mass is larger than 0.8M_{sun}_, most of them converge in ~120Myr. If stars rotate as rigid bodies, the angular momentum of the vast majority is within clearly outlined bounds. The lower boundary defines a terminal main sequence rotational isochrone, the upper one coincides with slow rotators from the Pleiades and stars from Praesepe delineate a third one. Mass dependent exponential relationships between angular momentum and age are determined from these isochrones. Age estimates based on the angular momentum, are acceptable in middle aged stars older than 750Myr and more massive than 0.6-0.7M_{sun}_. The evolution of the Rossby number indicates that the Parker dynamo may cease early on in stars where M/M_{sun}_>=1.1. An empirical formula for the torque, an idealized model for it and a relation between rotational period and magnetic field, lead to a formula for the evolution of the mass loss rate, predicting that the present solar rate is close to a minimum and that it was around five times more vigorous when life on Earth started.
  ***  

['Konishi M.', ' Matsuo T.', ' Yamamoto K.', ' Samland M.', ' Sudo J.', ' Shibai H.', ' Itoh Y.', ' Fukagawa M.', ' Sumi T.', ' Kudo T.', ' Hashimoto J.', ' Kuzuhara M.', ' Kusakabe N.', ' Abe L.', ' Akiyama E.', ' Brandner W.', ' Brandt T.D.', ' Carson J.C.', ' Feldt M.', ' Goto M.', ' Grady C.A.', ' Guyon O.', ' Hayano Y.', ' Hayashi M.', ' Hayashi S.S.', ' Henning T.', ' Hodapp K.W.', ' Ishii M.', ' Iye M.', ' Janson M.', ' Kandori R.', ' Knapp G.R.', ' Kwon J.', ' McElwain M.W.', ' Mede K.', ' Miyama S.', ' Morino J.-I.', ' Moro-Martin A.', ' Ishimura T.', ' Oh D.', ' Pyo T.-S.', ' Serabyn E.', ' Schlieder J.E.', ' Suenaga T.', ' Suto H.', ' Suzuki R.', ' Takahashi Y.H.', ' Takami M.', ' Takato N.', ' Terada H.', ' Thalmann C.', ' Turner E.L.', ' Watanabe M.', ' Wisniewski J.P.', ' Yamada T.', ' Takami H.', ' Usuda T.', ' Tamura M.']
We find a new substellar companion to the Pleiades member star, Pleiades HII 3441, using the Subaru telescope with adaptive optics. The discovery is made as part of the high-contrast imaging survey to search for planetary-mass and substellar companions in the Pleiades and young moving groups. The companion has a projected separation of 0.49+/-0.02 (66+/-2au) and a mass of 68+/-5MJ based on three observations in the J-, H-, and Ks-bands. The spectral type is estimated to be M7 (~2700K), and thus no methane absorption is detected in the H band. Our Pleiades observations result in the detection of two substellar companions including one previously reported among 20 observed Pleiades stars, and indicate that the fraction of substellar companions in the Pleiades is about 10.0^+26.1^_-8.8_%. This is consistent with multiplicity studies of both the Pleiades stars and other open clusters.
  ***  

['Prosser C.F.', ' Grankin K.N.']
We present the results from a photometric monitoring program of primarily solar-type open cluster stars obtained during 1994 and 1995. Several members of the {alpha} Persei cluster have been monitored and the corresponding relation between coronal x-ray activity and rotation period derived. The relation among mid-G/K type members illustrates both the previously noticed downturn in L_X_/L_bol_ at high rotation rates and the sharp decrease in coronal activity at long rotation periods as seen among Pleiades stars. Intensive observation of one slowly rotating G-type member of IC 4665 has enabled a period determination of 8-10 days to be made and illustrates the need for (and limitations of) high quality observations.
  ***  

['Pillitteri et al.']
This table contains the results from a deep X-ray survey of the young (~ 140 Myr), rich open cluster NGC 2516 obtained with the EPIC camera on board the XMM-Newton satellite. By combining the data from six observations, a high sensitivity, greater than a factor of 5 with respect to recent Chandra observations, has been achieved. Kaplan-Meier estimators of the cumulative X-ray luminosity distribution, statistically corrected for non-member contaminants, were built by the authors and compared to those of the nearly coeval Pleiades cluster. 431 X-ray sources were detected, and 234 of them have as optical counterparts cluster stars spanning the entire NGC 2516 main sequence. On the basis of X-ray emission and optical photometry, 20 new candidate members of the cluster have been identified; at the same time there are 49 X-ray sources without known optical or infrared counterpart. The X-ray luminosities of cluster stars span the range log L&lt;sub&gt;x&lt;/sub&gt; (erg s&lt;sup&gt;-1&lt;/sup&gt;) = 28.4 - 30.8. The representative coronal temperatures span the 0.3 - 0.6 keV (3.5 - 8 MK) range for the cool component and 1.0 - 2.0 keV (12 - 23 MK) for the hot one; similar values were found in other young open clusters like the Pleiades, IC 2391, and Blanco 1. While no significant differences were found in their X-ray spectra, NGC 2516 solar-type stars are definitely less luminous in X-rays than their nearly coeval Pleiades counterparts. The comparison with a previous ROSAT survey reveals the lack of variability amplitudes larger than a factor of 2 in solar-type cluster stars in a ~ 11 yr time scale, and thus activity cycles like in the Sun are probably absent or have a different period and amplitude in young stars. NGC 2516 has been observed several times with XMM-Newton during the first two years of satellite operations for calibration purposes. The observations used in this analysis span a period of 19 months with exposure times between 10 and 20 ks. All of these observations have been performed with the thick filter. In the combined EPIC datasets the authors detected 431 X-ray sources with a significance level greater than 5.0 sigma, which should lead statistically to at most one spurious source in the field of view.
  ***  

['Jeffries et al.']
This table contains a list of point sources detected by XMM-Newton EPIC in a pointing towards the young open cluster NGC 2547, made in order to allow the authors to characterize coronal activity in solar-type stars, and stars of lower mass, at an age of 30 Myr. X-ray emission was seen from stars at all spectral types, peaking among G stars at luminosities (0.3 - 3 keV) of L&lt;sub&gt;x&lt;/sub&gt; ~= 10&lt;sup&gt;30.5&lt;/sup&gt; erg/s and declining to L&lt;sub&gt;x&lt;/sub&gt; &lt;= 10&lt;sup&gt;29&lt;/sup&gt; erg/s among M stars with masses &gt;=0.2 solar masses. Coronal spectra show evidence for multi-temperature differential emission measures and low coronal metal abundances of Z~= 0.3. Most of the solar-type stars in NGC 2547 exhibit saturated or even supersaturated X-ray activity levels. The median levels of L&lt;sub&gt;x&lt;/sub&gt; and L&lt;sub&gt;x&lt;/sub&gt;/L&lt;sub&gt;bol&lt;/sub&gt; in the solar-type stars of NGC 2547 are very similar to those in T-Tauri stars of the Orion Nebula cluster (ONC), but an order of magnitude higher than in the older Pleiades. The spread in X-ray activity levels among solar-type stars in NGC 2547 is much smaller than in older or younger clusters. This table contains the properties of those X-ray sources which are correlated with optical cluster members (see Section 2.2 of the reference paper for details on the correlation procedure that was adopted), as well as the properties of those X-ray sources which are uncorrelated with any optical cluster members. The table lists the cross-identifications with optical catalogs for the candidate cluster sources along with their X-ray luminosities and X-ray to bolometric flux ratios, as well as the correlations between cluster members which were detected by XMM-Newton and those detected 7 years earlier by the ROSAT HRI instrument, along with the X-ray luminosities and flux ratios as determined by the HRI.
  ***  

['Giardino et al.']
This table provides a list of X-ray sources detected in a ~140 ks Chandra X-ray observation of the open cluster NGC 752. For the sources with 2MASS counterparts, the values of their magnitudes in the J, H and K bands are also given. Very little is known about the evolution of stellar activity between the ages of the Hyades (0.8 Gyr) and the Sun (4.6 Gyr). To gain information on the typical level of coronal activity at a star&#39;s intermediate age, the authors have studied the X-ray emission from stars in the 1.9 Gyr-old open cluster NGC 752. They analyzed a ~ 140 ks Chandra observation of NGC 752 and a ~50 ks XMM-Newton observation of the same cluster. They detected 262 X-ray sources in the Chandra data and 145 sources in the XMM-Newton observation. Around 90% of the catalogued cluster members within Chandr&aacute;s field of view are detected in the X-ray observation. The X-ray luminosity of all observed cluster members (28 stars) and of 11 cluster member candidates was derived. These data indicate that, at an age of 1.9 Gyr, the typical X-ray luminosity L&lt;sub&gt;x&lt;/sub&gt; of the cluster members with masses of 0.8 to 1.2 solar masses is 1.3 x 10&lt;sup&gt;28&lt;/sup&gt; erg s&lt;sup&gt;-1&lt;/sup&gt;, which is approximately a factor of 6 times less intense than that observed in the younger Hyades. Given that L&lt;sub&gt;x&lt;/sub&gt; is proportional to the square of a star&#39;s rotational rate, the median L&lt;sub&gt;x&lt;/sub&gt; of NGC 752 is consistent, for t &gt;= 1 Gyr, with a decaying rate in rotational velocities v&lt;sub&gt;rot&lt;/sub&gt; ~ t&lt;sup&gt;-alpha&lt;/sup&gt; with alpha ~ 0.75, steeper than the Skumanich relation (alpha ~ 0.5) and significantly steeper than that observed between the Pleiades and the Hyades (where alpha &lt;0.3), suggesting that a change in the rotational regimes of the stellar interiors is taking place at an age of ~ 1 Gyr. The 135 ks observation of NGC 752 was performed by the Chandra ACIS camera on September 29, 2003 starting at 21:11:59 UT. The X-ray source detection was performed on the event list using the Wavelet Transform detection algorithm developed at Palermo Astronomical Observatory PWDETECT, available at &lt;a href="http://oapa.astropa.unipa.it/progetti_ricerca/PWDetect"&gt;http://oapa.astropa.unipa.it/progetti_ricerca/PWDetect&lt;/a&gt;. Initially, the energy range 0.2 - 10 keV was selected and the threshold for source detection was taken as to ensure a maximum of 1-2 spurious sources per field. 169 sources were detected in this way. The analysis of these sources hardness ratios showed, however, that all the catalogued stars in the field had low hardness ratios, HR &lt; ~ 0.2, where HR is the number of photons in the 2 - 8 keV band over the number in the 0.5 - 2 keV band. Thus, to maximize the detection of stellar sources, PWDETECT was applied to the event list in the energy range from 0.5 - 2 keV. Using a detection threshold which ensures less than 1 spurious source per field leads to the detection of 188 sources, while lowering this threshold to 10 spurious sources per field, allows 262 sources to be identified in this energy range. This is a significant increase (well above the number expected if all the additional sources were spurious), thus the authors retained this list of 262 sources as their final list of sources in the NGC 752 field, with the caveat that ~ 10 sources among them are likely spurious. Note that the existence of ~ 10 spurious sources in the list is not so much of a problem in this context, because cluster members or candidate members are identified by the existence of a visible or near-IR counterpart. The authors searched for 2MASS counterparts to the X-ray sources using the 2MASS Point Source Catalogue (PSC) and a search radius of 3 arcsec and found a counterpart for 43 sources. Searching within the Point Source Reject Table of the 2MASS Extended Mission leads to the further identification of 1 counterpart (source number 87).
  ***  

['Giardino et al.']
This table provides a list of X-ray sources detected in a ~50 ks XMM-Newton X-ray observation of the open cluster NGC 752. For the sources with 2MASS counterparts, the values of their magnitudes in the J, H and K bands are also given. Additionally, for the sources with a Chandra counterpart (within a search radius of 5 arcsec), the values of their Chandra source number (as given in the related Browse table NGC752CXO) are also given. Very little is known about the evolution of stellar activity between the ages of the Hyades (0.8 Gyr) and the Sun (4.6 Gyr). To gain information on the typical level of coronal activity at a star&#39;s intermediate age, the authors have studied the X-ray emission from stars in the 1.9 Gyr-old open cluster NGC 752. They analyzed a ~ 140 ks Chandra observation of NGC 752 and a ~50 ks XMM-Newton observation of the same cluster. They detected 262 X-ray sources in the Chandra data and 145 sources in the XMM-Newton observation. Around 90% of the catalogued cluster members within Chandr&aacute;s field of view are detected in the X-ray observation. The X-ray luminosity of all observed cluster members (28 stars) and of 11 cluster member candidates was derived. These data indicate that, at an age of 1.9 Gyr, the typical X-ray luminosity L&lt;sub&gt;x&lt;/sub&gt; of the cluster members with masses of 0.8 to 1.2 solar masses is 1.3 x 10&lt;sup&gt;28&lt;/sup&gt; erg s&lt;sup&gt;-1&lt;/sup&gt;, which is approximately a factor of 6 times less intense than that observed in the younger Hyades. Given that L&lt;sub&gt;x&lt;/sub&gt; is proportional to the square of a star&#39;s rotational rate, the median L&lt;sub&gt;x&lt;/sub&gt; of NGC 752 is consistent, for t &gt;= 1 Gyr, with a decaying rate in rotational velocities v&lt;sub&gt;rot&lt;/sub&gt; ~ t&lt;sup&gt;-alpha&lt;/sup&gt; with alpha ~ 0.75, steeper than the Skumanich relation (alpha ~ 0.5) and significantly steeper than that observed between the Pleiades and the Hyades (where alpha &lt;0.3), suggesting that a change in the rotational regimes of the stellar interiors is taking place at an age of ~ 1 Gyr. NGC 752 was observed for 49 ks by the XMM-Newton EPIC camera on February 5, 2003 starting at 23:29:25 UT, and the nominal pointing was towards J2000.0 RA and Declination of (01:57:38, +37:47:60), thus the XMM-Newton field-of-view (FOV) includes the Chandra FOV. For the source detection, the authors used the PWXDETECT code developed at Palermo Observatory and derived from the analogous Chandra PWDETECT code based on wavelet transform analysis. This allows the three EPIC exposures (PN, MOS1 and MOS2) to be combined in order to gain a deeper sensitivity with respect to the source detection based on single images. There were 145 point sources detected in the energy band 0.5 - 2.0 keV. An extended source (not listed in this present table), very likely a galaxy cluster, is also visible in the EPIC data. The authors searched for 2MASS counterparts to the XMM-Newton sources using a search radius of 5 arcsec and found a counterpart for 38 sources. As for the Chandra data, all sources with a visible counterpart from DLM94 have also a 2MASS counterpart, so this leaves 15 XMM-Newton sources with a 2MASS counterpart and no counterpart in Daniel et al. (1994, PASP, 106, 281); of these, 3 were also detected by Chandra; of the other 12, 10 are outside the Chandra FOV, while two are within it (XMM-Newton sources 58 and 65). Source 65 was caught by XMM-Newton during the decay phase of a flare, which explains why it is not detected in the Chandra data. For source 58 there is no immediate explanation for this, since the light curve does not show evidence of a flare. No additional near-IR counterpart to the XMM-Newton sources was found within the Point Source Reject Table of the 2MASS Extended Mission.
  ***  

['Micela et al.']
This catalog contains the results of a deep X-ray survey of the core region of the Pleiades open cluster carried out with ROSAT. In a single PSPC field (~1 degree in radius), 99 of 214 Pleiades stars are detected in X-rays, and upper limits are computed for the remainder. This catalog lists the characteristics of these stars taken from the literature, including their rotational data, as well as their X-ray characteristics. The nucleus of the composite catalog used in this study is the catalog compiled from the published literature for the Einstein investigations of the Pleiades (Micela et al. 1990, ApJ, 348, 557). This list has been extended by the results of recent surveys to a completeness limit of visual magnitude of about 18.

RESULT: Based on these, the second one (by Eichhorn et al) looks like a good start.

At this point, you can proceed to Step 2#

– OR –

Try a different data discovery method#

Alternative Method: Use ADS to search for appropriate paper and access data via NED#

There are multiple paths for the data discovery. So it may also be that you know the paper that has the data you are interested in and want to access via the bibcode or authors, etc.

In this case, let’s assume that we have the information that the Eichhorn+1970 paper has the data that we need to create the H-R diagram: https://ui.adsabs.harvard.edu/abs/1970MmRAS..73..125E/abstract

We can either search by bibcode (1970MmRAS..73..125E) or “Eichhorn” to get the access_urls that will allow us to work with the data.

Before this step, if may help to see the names of the fields available to use. Notice the following fields:

“source_value” contains the bibcode information that we want; “creator_seq” lists the authors;

and

“access_url” provides the url from where the data can be accessed.

## You already have this from above:
# tap_services = registry.search(servicetype='tap', keywords=['star pleiades'],
#                                ucd = ['phot.mag%'], includeaux=True)
print(tap_services.fieldnames)

('ivoid', 'res_type', 'short_name', 'res_title', 'content_level', 'res_description', 'reference_url', 'creator_seq', 'created', 'updated', 'rights', 'content_type', 'source_format', 'source_value', 'region_of_regard', 'waveband', 'access_urls', 'standard_ids', 'intf_types', 'intf_roles', 'alt_identifier')

First, Try using bibcode:

bibcode = '1970MmRAS..73..125E' # Eichhorn
idx=-1
for s in tap_services:
    idx+=1
    if bibcode in s['source_value']:
        myidx=idx
        print(f"{s.short_name}, {s.source_value}, {s.access_url}")
        break
#  Note that using the to_table() lets you search the result
#   easily using all columns.  But in the end, you want to get
#   back not an astropy table row, which you cannot use, but the
#   original RegistryResult that has the callable TAP service.
myTAP=tap_services[myidx]

I/90, 1970MmRAS..73..125E, http://tapvizier.cds.unistra.fr/TAPVizieR/tap

Note that the URL is a generic TAP url for Vizier. All of its tables can be accessed by that same TAP services. It’ll be in the ADQL query itself that you specify the table name. We’ll see this below.

Next, try using Author name:

author = 'Eichhorn'

for record in tap_services:
    names=record.creators
    if 'Eichhorn' in names[0]:
        print("For %s: " %record.short_name)
        print("     Access URL: %s" %record['access_urls'][0])
        print("     Reference URL: %s" %record.reference_url)

For I/90: 
     Access URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap
     Reference URL: https://cdsarc.cds.unistra.fr/viz-bin/cat/I/90

In the code above, the record is a Registry Resource. You can access the attribute, “creators”, from the resource, which is relevant for our example here since this is a direct way to get the author names. The other attributes, “access_url” and “reference_url”, provides two types of URLs. The former can be used to access the service resource (as described above) and the latter points to a human-readable document describing this resource.

If you click on the Reference URL links, you can find the abstract, Readme file, Vizier table, and much more information associated with this catalog.

Additional information about PyVO Registry Resource and its attributes is available from this page.

***

These examples provide a few ways to access the information of interest.

Below are a few other ways to see what the tap_service table contains.

To view the column information: tap_services.to_table().columns() shows the metadata contained in the tap service. We will reference some of this columns below as we try to find the appropriate table.
tap_services[index].describe(): The table with the tap_services output has, in our case, 83 tables listed and each includes metadata containing some human readable description. You can get the description for one case or for all the records by iterating through the resource. In the former case, we show the description for the Eichhorn data, whose index is uniq_ind[1]. The latter case also follows.

print( tap_services.to_table().columns )

<TableColumns names=('ivoid','res_type','short_name','res_title','content_level','res_description','reference_url','creator_seq','created','updated','rights','content_type','source_format','source_value','region_of_regard','waveband','access_urls','standard_ids','intf_types','intf_roles','alt_identifier')>

tap_services[uniq_ind[1]].describe()   # For Eichhorm+1970 example.

Positions of 502 Stars in Pleiades Region
Short Name: I/90
IVOA Identifier: ivo://cds.vizier/i/90
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

The catalog contains the positions (equinox B1900.0 and epoch B1955.0) of 502
stars in a region of about 1.5 degrees square in the Pleiades cluster,
centered on Eta Tau. These coordinates have been derived from measurements of
stellar images obtained with 65 exposures of various durations on 14
photographic plates with two telescopes at McCormick Observatory and Van Vleck
Observatory. The plates were reduced by the plate overlap method, which
resulted in a high degree of systematic accuracy in the final positions. Data
in the machine version include Hertzsprung number, color index, photovisual
magnitude, right ascension and declination and their standard errors, proper
motion, and differences between the present position and previous works. Data
for exposures, plates, and images measured, present in the published catalog,
are not included in the machine version.

Waveband Coverage: optical

# To iterate over all the tables:
for tapsvc in tap_services:
    print("---------------------------------------------  \n")
    tapsvc.describe()

---------------------------------------------  

US Naval Observatory Pleiades Catalog
Short Name: I/163
IVOA Identifier: ivo://cds.vizier/i/163
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

This catalog is a special subset of the Eichhorn et al. (1970) Pleiades
catalog (see <I/90>) updated to B1950.0 positions and with proper motions
added. It was prepared for the purpose of predicting occultations of Pleiades
stars by the Moon, but is useful for general applications because it contains
many faint stars not present in the current series of large astrometric
catalogs.

Waveband Coverage: optical
---------------------------------------------  

Positions of 502 Stars in Pleiades Region
Short Name: I/90
IVOA Identifier: ivo://cds.vizier/i/90
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

The catalog contains the positions (equinox B1900.0 and epoch B1955.0) of 502
stars in a region of about 1.5 degrees square in the Pleiades cluster,
centered on Eta Tau. These coordinates have been derived from measurements of
stellar images obtained with 65 exposures of various durations on 14
photographic plates with two telescopes at McCormick Observatory and Van Vleck
Observatory. The plates were reduced by the plate overlap method, which
resulted in a high degree of systematic accuracy in the final positions. Data
in the machine version include Hertzsprung number, color index, photovisual
magnitude, right ascension and declination and their standard errors, proper
motion, and differences between the present position and previous works. Data
for exposures, plates, and images measured, present in the published catalog,
are not included in the machine version.

Waveband Coverage: optical
---------------------------------------------  

Tonantzintla Pleiades Flare Stars
Short Name: II/131
IVOA Identifier: ivo://cds.vizier/ii/131
Access modes: tap#aux
Multi-capability service -- use get_service()

The original catalog lists the flare stars discovered by different
astronomical observatories over an area slightly larger than 20 square degrees
in the Pleiades regions centered on Alcyone. Not all the flare stars are
members of this cluster, membership indicators are provided in the catalog.
The catalog, combining Tables 1 and 2 of the publication, gives the data for
1531 flares of 519 flare stars.

Waveband Coverage: optical
---------------------------------------------  

K-Line photometry of stars in Population I clusters
Short Name: II/44
IVOA Identifier: ivo://cds.vizier/ii/44
Access modes: tap#aux
Multi-capability service -- use get_service()

Photoelectric photometry of the K-line of calcium has been performed for the A
stars of five open clusters (Hyades, Pleiades, IC 2391, IC 2602, and NGC 6475)
and one association (Orion). All observations were carried out simultaneously
with the field stars measurements in Paper II (II/43), with the 16-inch (40cm)
and 36-inch (91cm) telescopes of the Cerro Tololo Inter-American Observatory,
between May 1969 and January 1970.

Waveband Coverage: optical
---------------------------------------------  

Pleiades field Membership probabilities
Short Name: J/A+A/299/696
IVOA Identifier: ivo://cds.vizier/j/a+a/299/696
Access modes: tap#aux
Multi-capability service -- use get_service()

A catalogue of proper motions and photographic B,V magnitudes for stars up to
B=19 mag within a region centered near Alcyone is presented. The catalogue is
based on MAMA measurements of 8 plates taken with the Tautenburg Schmidt
telescope. The survey includes ca. 14500 stars and covers a total field of
about 9 square degrees. Membership probabilities, proper motions and B,V
magnitudes are listed for 442 stars up to B=19 mag in the Pleiades field.

Waveband Coverage: optical
---------------------------------------------  

Radial velocities of Pleiades members
Short Name: J/A+A/320/74
IVOA Identifier: ivo://cds.vizier/j/a+a/320/74
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

The analysis of CORAVEL radial velocities of 93 stars selected on the basis of
their proper motion and Geneva CCD photometric observations for 57 stars have
permitted to identify 25 new members in the outer part of the Pleiades.
Several spectroscopic binaries have been discovered, but their membership is
not clear. Two orbits with short periods have been determined, but both stars
are probably non-members. The total number of member stars in the outer part
of the Pleiades in the spectral range F5-K0 (0.45<B-V<0.90) is now 81 which is
comparable to the number of stars known in Hertzsprung's central area (88
stars) in the same spectral domain. Therefore at least 48% of the F5-K0 main-
sequence stars are located in the outer part of the cluster. And the census is
probably still incomplete.

Waveband Coverage: optical
---------------------------------------------  

K magnitude of Pleiades low-mass binaries
Short Name: J/A+A/323/139
IVOA Identifier: ivo://cds.vizier/j/a+a/323/139
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

This table provides the list of stars observed but not resolved during the
diffraction-limited survey of G and K Pleiades dwarfs. Previously known
binaries, either photometric or spectroscopic, are referenced.

Waveband Coverage: optical
---------------------------------------------  

Masses of Pleiades members
Short Name: J/A+A/329/101
IVOA Identifier: ivo://cds.vizier/j/a+a/329/101
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

On the basis of the best available member list and duplicity information, we
have studied the radial distribution of 270 stars and multiple systems earlier
than K0 in the Pleiades. Five new long period spectroscopic binaries have been
identified from the CORAVEL observations. We have found a clear mass
segregation between binaries and single stars, which is explained by the
greater average mass of the multiple systems. The mass function of the single
stars and primaries appears to be significantly different. While the central
part of the cluster is spherical, the outer part is clearly elliptical, with
an ellipticity of 0.17. The various parameters describing the Pleiades are
(for a distance of 125pc): core radius r_c_=0.6 deg (1.4pc), tidal radius
r_t_=7.4 (16pc), half mass radius r_m/2_=0.88 (1.9pc), harmonic radius r=1.82
(4pc). Low-mass stars (later than K0) probably extend further out and new
proper motion and radial velocity surveys over a larger area and to fainter
magnitudes would be very important to improve the description of the cluster
structure and complete mass function.

Waveband Coverage:
---------------------------------------------  

Pleiades member list
Short Name: J/A+A/332/575
IVOA Identifier: ivo://cds.vizier/j/a+a/332/575
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

The luminosity function (LF) of the Pleiades cluster stars was constructed for
the study of the LF fine structure related to pre-main sequence (MS) stellar
evolution. Theoretical luminosity functions based on present-day pre-MS and MS
stellar models were constructed and compared with observations. We tested both
power- and log-normal laws describing the cluster star Initial Mass Function
(IMF). Both single star formation burst- and age spread-models were examined.
The agreement between the observed Pleiades colour-magnitude diagram with the
new HIPPARCOS distance and the theoretical ZAMS for a normal metallicity is
excellent when the model positions in the HR diagram are corrected to the
helium abundance Y=0.34. The corresponding age of the cluster is logt=7.95.
Three features (dips) were found in the observed cluster LF in a magnitude
range M_V_=5-12mag. Two of them (at M_V_=7.5mag and 9.5mag) are assumed to be
field LF features: Wielen and Kroupa dips. Theoretical models fail to
reproduce them. We attributed the third (brightest) detail (the dip at
M_V_=5.5mag) to the pre-MS evolution of Pleiades stars. The observed Pleiades
LF corresponds in its brighter part to the standard Population I IMF. The log-
normal IMF fits the observations much better than a simple power-law IMF. The
brightest LF feature could be reproduced in the theoretical LF if a
substantial age spread of order of several tens of Myrs is supposed to exist
among the Pleiades stars.

Waveband Coverage: optical
---------------------------------------------  

Mass segregation in open clusters
Short Name: J/A+A/333/897
IVOA Identifier: ivo://cds.vizier/j/a+a/333/897
Access modes: tap#aux
Multi-capability service -- use get_service()

On the basis of the best available member list and duplicity information, we
have studied the radial structure of Praesepe and of the very young open
cluster NGC 6231. We have found mass segregation among the cluster members and
between binaries and single stars, which is explained by the greater average
mass of the multiple systems. However, the degree of mass segregation for
stars between 1.5 and 2.3M_{sun}_ is less pronounced in Praesepe than in the
Pleiades. Furthermore, mass segregation is already present in the very young
open cluster NGC 6231 although this cluster is likely still not dynamically
relaxed. We discuss the implications of these results and propose a
qualitative scenario for the evolution of mass segregation in open clusters.
In Praesepe the mass function of single stars and primaries appears to be
significantly different, like in the Pleiades. We observe an absence of
ellipticity of the outer part of Praesepe.

Waveband Coverage: optical
---------------------------------------------  

ROSAT HRI observations of the Pleiades
Short Name: J/A+A/341/751
IVOA Identifier: ivo://cds.vizier/j/a+a/341/751
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

In a deep X-ray survey of the Pleiades open cluster, we use the ROSAT High
Resolution Imager to explore a region of the cluster formerly surveyed with
the PSPC. These new observations substantially improve upon both the
sensitivity and the spatial resolution for this region of the Pleiades,
allowing us to detect 18 cluster members not detected before and 16 members
not included in the catalogs used in previous surveys. The high sensitivity of
the present observations permits us to obtain more stringent upper limits for
72 additional members and also provides sufficient numbers of stars to enable
us to explore the dependence of L_x_ on stellar rotation for the slow rotators
of the Pleiades. Using the new high sensitivity X-ray observations and the
recent rotational measurements we discuss the activity-rotation relationship
in the Pleiades solar type stars. We also present new photometric observations
of optical counterparts of a number of X-ray sources detected in previous
surveys but not yet identified.

Waveband Coverage: x-ray
---------------------------------------------  

Photometry in NGC 2516
Short Name: J/A+A/375/863
IVOA Identifier: ivo://cds.vizier/j/a+a/375/863
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

We present the results of a 0.86 square degree CCD photometric survey of the
open cluster NGC 2516, which has an age of about 150Myr and may have a much
lower metallicity than the similarly-aged Pleiades. Our BVI_c_ survey of
cluster members is complete to V~20 and is used to select a preliminary
catalogue of 1254 low mass (0.<M<2.0M_{sun}_) cluster candidates, of which
about 70-80 percent are expected to be genuine. After applying corrections for
contamination by non-members and adding data for higher mass stars from the
literature, we investigate the cluster binarity, luminosity and mass function,
mass segregation and total mass. We find a binary fraction of 26+/-5%, for A
to M-type systems with mass ratios between 0.6 and 1, which is very similar to
the Pleiades.

Waveband Coverage: optical
---------------------------------------------  

Starspot cycles of six young solar analogues
Short Name: J/A+A/393/225
IVOA Identifier: ivo://cds.vizier/j/a+a/393/225
Access modes: tap#aux
Multi-capability service -- use get_service()

A long-term photometric monitoring of a selected sample of solar analogues has
been carried out since early nineties as part of "The Sun in tim" project,
which is aimed at a multiwavelength study of stars with solar-like global
properties, but with different ages and thus at different stages of their
evolution. The extended time sequence of ground-based observations collected
over more than a decade as part of this program has revealed the existence of
starspot cycles. Also from these data it is possible to investigate surface
differential rotation of the stars. In this paper we present the photometry
collected to date and report on cycles search for a selected subsample of five
young single G0-G5V stars with ages between ~130Myr and 700Myr: EK Dra,
{pi}^1^ UMa, HN Peg, {kappa}^1^ Cet, BE Cet. Also we include in this study the
Pleiades-age (~130Myr) K0V star DX Leo (HD 82443). All the cited stars show
activity cycles whose period is, furthermore, the first determined from
photometric data. They are compared to those activity cycles derived from CaII
H&K emission fluxes and differences are discussed. All the cycle periods,
except for EK Dra, fit well the empirical relations with global stellar
parameters derived from larger stellar samples. The following results are also
inferred from the present study: i) the fastest rotating stars tend to have
longer cycles; ii) the range in the observed cycle lengths seems to converge
with stellar age from a maximum dispersion around the Pleiades' age towards
the solar cycle value at the Sun's age; iii) the overall short- and long-term
photometric variability increases with inverse Rossby number with very high
correlation degree, indicating that the level of magnetic activity at least in
photosphere is still controlled by the stellar rotation even on the longest
time scales; iiii) the increase with inverse Rossby number of the long-term
overall photometric variability seems to level off at the highest rotation
rate, which may be interpreted as due to a saturation in the level of
photospheric magnetic activity around the activity maximum.

Waveband Coverage:
---------------------------------------------  

Activity-rotation relationship in stars
Short Name: J/A+A/397/147
IVOA Identifier: ivo://cds.vizier/j/a+a/397/147
Access modes: tap#aux
Multi-capability service -- use get_service()

We present the results of a new study on the relationship between coronal
X-ray emission and stellar rotation in late-type main-sequence stars. We have
selected a sample of 259 dwarfs in the B-V range 0.5-2.0, including 110 field
stars and 149 members of the Pleiades, Hyades, {alpha} Persei, IC 2602 and IC
2391 open clusters. All the stars have been observed with ROSAT, and most of
them have photometrically-measured rotation periods available. Our results
confirm that two emission regimes exist, one in which the rotation period is a
good predictor of the total X-ray luminosity, and the other in which a
constant saturated X-ray to bolometric luminosity ratio is attained; we
present a quantitative estimate of the critical rotation periods below which
stars of different masses (or spectral types) enter the saturated regime.

Waveband Coverage: x-ray, optical
---------------------------------------------  

X-ray emission in cool main sequence stars
Short Name: J/A+A/410/671
IVOA Identifier: ivo://cds.vizier/j/a+a/410/671
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

The maximum amplitude A_max_ of spot-induced brightness variations from long-
term V-band photometry and the ratio L_X_/L_bol_ between X-ray and bolometric
luminosities are suitable indicators of the level of magnetic activity in the
photosphere and in the corona of late-type stars, respectively. By using these
activity indicators we investigate the dependence of coronal X-ray emission on
the level of photospheric starspot activity in a homogeneous sample of low
mass main-sequence field and cluster stars of different ages (IC 2602, IC
4665, IC 2391, {alpha} Per, Pleiades and Hyades).

Waveband Coverage: x-ray
---------------------------------------------  

Spectrocopic results on ROSAT late-type stars
Short Name: J/A+A/433/151
IVOA Identifier: ivo://cds.vizier/j/a+a/433/151
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

We present results of an investigation of the X-ray properties, age
distribution, and kinematical characteristics of a high-galactic latitude
sample of late-type field stars selected from the ROSAT All-Sky Survey (RASS).
The sample comprises 254 RASS sources with optical counterparts of spectral
types F to M distributed over six study areas located at |b|>~20{deg}, and
Dec>=-9{deg}. A detailed study was carried out for the subsample of ~200 G, K,
and M stars. Lithium abundances were determined for 179 G-M stars. Radial
velocities were measured for most of the 141 G and K type stars of the sample.
Combined with proper motions these data were used to study the age
distribution and the kinematical properties of the sample. Based on the
lithium abundances half of the G-K stars were found to be younger than the
Hyades (660Myr). About 25% are comparable in age to the Pleiades (100Myr). A
small subsample of 10 stars is younger than the Pleiades. They are therefore
most likely pre-main sequence stars. Kinematically the PMS and Pleiades-type
stars appear to form a group with space velocities close to the Castor moving
group but clearly distinct from the Local Association.

Waveband Coverage: x-ray, optical
---------------------------------------------  

XMM survey of NGC 2516
Short Name: J/A+A/450/993
IVOA Identifier: ivo://cds.vizier/j/a+a/450/993
Access modes: tap#aux
Multi-capability service -- use get_service()

We report a deep X-ray survey of the young (~140Myr), rich open cluster NGC
2516 obtained with the EPIC camera on board the XMM-Newton satellite. By
combining data from six observations, a high sensitivity, greater than a
factor of 5 with respect to recent Chandra observations, has been achieved.
Kaplan-Meier estimators of the cumulative X-ray luminosity distribution are
built, statistically corrected for non members contaminants and compared to
those of the nearly coeval Pleiades. The EPIC spectra of the X-ray brightest
stars are fitted using optically thin model plasma with one or two thermal
components. We detected 431 X-ray sources and 234 of them have as optical
counterparts cluster stars spanning the entire NGC 2516 Main Sequence.

Waveband Coverage: x-ray
---------------------------------------------  

Geneva photometry of HD 23642
Short Name: J/A+A/463/579
IVOA Identifier: ivo://cds.vizier/j/a+a/463/579
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

HD 23642 is the only known eclipsing binary in the Pleiades, and therefore of
importance in determining the distance to this cluster. To use new photometric
and spectroscopic data in combination with existing data in the literature in
order to improve the determination of the parameters of the system, its
distance and reddening. New photometric and spectroscopic data are presented
for HD 23642. The spectroscopic data are ``spectrally disentangled'' using the
KOREL code. The new and literature photometric and radial velocity data are
simultaneously analysed using the FOTEL code to obtain the orbital solution
and derive the fundamental parameters of the two stars. The distance and
reddening are determined by fitting 7-colour Geneva, B,V and Stroemgren
colours, and considering surface-brightness relations for the two components
in (B-V) and Stroemgren c_1_-index. The preferred distance is 138.0+/-1.5pc
for a reddening of E(B-V)=0.025+/-0.003. The reddening value is larger than
the 0.012 adopted in the recent works on this stars by Munari et al.
(2004A&A...418L..31M) and Southworth et al. (2005A&A...429..645S), and smaller
than other values in the literature for the cluster reddening. The distance is
in agreement with other recent works on the distance to the Pleiades. A
comparison with evolutionary models suggests that the inclusion of convective
core overshoot gives a much better fit to the empirical mass-radius
relationship obtained from the binary analysis. Both this comparison and the
"spectral disentangling" are consistent with HD 23642 having [Fe/H]=+0.06, a
value determined by the most recent spectroscopical analyses of Pleiades
stars.

Waveband Coverage: optical
---------------------------------------------  

Velocities of F-G-K stars in Blanco 1
Short Name: J/A+A/485/95
IVOA Identifier: ivo://cds.vizier/j/a+a/485/95
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

The nearby open cluster Blanco 1 is of considerable astrophysical interest for
formation and evolution studies of open clusters because it is the third
highest Galactic latitude cluster known. It has been observed often, but so
far no definitive and comprehensive membership determination is readily
available. An observing programme was carried out to study the stellar
population of Blanco 1, and especially the membership and binary frequency of
the F5-K0 dwarfs. We obtained radial-velocities with the CORAVEL spectrograph
in the field of Blanco 1 for a sample of 148 F-G-K candidate stars in the
magnitude range 10<V<14. New proper motions and UBVI CCD photometric data from
two extensive surveys were obtained independently and are used to establish
reliable cluster membership assignments in concert with radial-velocity data.
The membership of 68 stars is confirmed on the basis of proper motion, radial
velocity, and photometric criteria. Fourteen spectroscopic- and suspected
binaries (2 SB2s, 9 SB1s, 3SB?) have been discovered among the confirmed
members. Thirteen additional stars are located above the main sequence or
close to the binary ridge, with radial velocities and proper motions
supporting their membership. These are probable binaries with wide
separations. Nine binaries (7 SB1 and 2 SB2) were detected among the field
stars. The spectroscopic binary frequency among members is 20% (14/68);
however, the overall binary rate reaches 40% (27/68) if one includes the
photometric binaries. The cluster mean heliocentric radial velocity is
+5.53+/-0.11km/s based on the most reliable 49 members. The Vsini distribution
is similar to that of the Pleiades, confirming the age similarities between
the two clusters.

Waveband Coverage: optical, infrared
---------------------------------------------  

RACE-OC project: YSOs within 100pc
Short Name: J/A+A/520/A15
IVOA Identifier: ivo://cds.vizier/j/a+a/520/a15
Access modes: tap#aux
Multi-capability service -- use get_service()

Examining the angular momentum of stars and its interplay with their magnetic
fields represent a promising way to probe the stellar internal structure and
evolution of low-mass stars. We attempt to determine the rotational and
magnetic-related activity properties of stars at different stages of
evolution.We focused our attention primarily on members of clusters and young
stellar associations of known ages. In this study, our targets are 6 young
loose stellar associations within 100pc and with ages in the range 8-70Myr: TW
Hydrae (~8Myr), beta Pictoris (~10Myr), Tucana/Horologium, Columba, Carina
(~30Myr), and AB Doradus (~70Myr). Additional rotational data for alpha Persei
and the Pleiades from the literature are also considered.

Waveband Coverage: optical
---------------------------------------------  

Photometry and proper motions in IC4665
Short Name: J/A+A/532/A103
IVOA Identifier: ivo://cds.vizier/j/a+a/532/a103
Access modes: tap#aux
Multi-capability service -- use get_service()

Knowledge of the mass function in open clusters constitutes one way to
constrain the formation of low-mass stars and brown dwarfs along with the
knowledge of the frequency of multiple systems and the properties of disks.
The aim of the project is to determine the shape of the mass function in the
low-mass and substellar regimes in the pre-main sequence (27Myr) cluster
IC4665 located at 350pc from the Sun. We have cross-matched the near-infrared
photometric data from the Eighth Data Release (DR8) of the UKIRT Infrared Deep
Sky Survey (UKIDSS) Galactic Clusters Survey (GCS) with previous optical data
obtained with the Canada-France-Hawaii (CFH) wide-field camera to improve the
determination of the luminosity and mass functions in the low-mass and
substellar regimes. The availability of i and z photometry taken with the
CFH12K camera on the Canada France Hawaii Telescope added strong constraints
to the UKIDSS photometric selection in this cluster located in a dense region
of our Galaxy. We have derived the luminosity and mass functions of the
cluster down to J=18.5mag, corresponding to masses of ~0.025M_{sun}_ at the
distance and age of IC4665 according to theoretical models. In addition, we
have extracted new candidate members down to ~20 Jupiter masses in a
previously unstudied region of the cluster. We have derived the mass function
over the 0.6-0.04M_{sun}_ mass range and found that it is best represented by
a log-normal function with a peak at 0.25-0.16M_{sun}_, consistent with the
determination in the Pleiades.

Waveband Coverage: optical, infrared
---------------------------------------------  

Observational properties of Hipparcos stars
Short Name: J/A+A/595/A59
IVOA Identifier: ivo://cds.vizier/j/a+a/595/a59
Access modes: tap#aux
Multi-capability service -- use get_service()

Since the release of the Hipparcos catalogue in 1997, the distance to the
Pleiades open cluster has been heavily debated. The distance obtained from
Hipparcos and those by alternative methods differ by 10 to 15%. As accurate
stellar distances are key to understanding stellar structure and evolution,
this dilemma puts the validity of some stellar evolution models into question.
Using our model-independent method to determine parallaxes based on twin
stars, we report individual parallaxes of 15 FGK type stars in the Pleiades in
anticipation of the astrometric mission Gaia. These parallaxes give a mean
cluster parallax of 7.42+/-0.09mas,which corresponds to a mean cluster
distance of 134.8+/-1.7pc. This value agrees with the current results obtained
from stellar evolution models.

Waveband Coverage: optical, infrared
---------------------------------------------  

The Seven Sisters DANCe. II. Pleiades
Short Name: J/A+A/596/A113
IVOA Identifier: ivo://cds.vizier/j/a+a/596/a113
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

Stellar clusters are open windows to understand stellar evolution.
Specifically, the change with time and the dependence on mass of different
stellar properties. As such, they are our laboratories where different
theories can be tested. We try to understand the origin of the connection
between lithium depletion in F, G and K stars, rotation and activity, in
particular in the Pleiades open cluster. We have collected all the relevant
data in the literature, including information regarding rotation period,
binarity and activity, and cross-matched with proper motions, multi-wavelength
photometry and membership probability from the DANCe database. In order to
avoid biases, only Pleiades single members with probabilities larger than 75%
have been included in the discussion. Results. The analysis confirms that
there is a strong link between activity, rotation and the lithium equivalent
width excess, specially for the range Lum(bol)=0.5-0.2L_{sun}_ (about K2-K7
spectral types or 0.75-0.95M_{sun}_). It is not possible to disentangle these
effects but we cannot exclude that the observed lithium overabundance is
partially an observational effect due to enhanced activity, due to a large
coverage by stellar spots induced by high rotation rates. Since a bona fide
lithium enhancement is present in young, fast rotators, both activity and
rotation should play a role in the lithium problem.

Waveband Coverage:
---------------------------------------------  

Gaia DR1 open cluster members
Short Name: J/A+A/601/A19
IVOA Identifier: ivo://cds.vizier/j/a+a/601/a19
Access modes: tap#aux
Multi-capability service -- use get_service()

The first Gaia Data Release contains the Tycho-Gaia Astrometric Solution
(TGAS). This is a subset of about 2 million stars for which, besides the
position and photometry, the proper motion and parallax are calculated using
Hipparcos and Tycho-2 positions in 1991.25 as prior information. We
investigate the scientific potential and limitations of the TGAS component by
means of the astrometric data for open clusters. Mean cluster parallax and
proper motion values are derived taking into account the error correlations
within the astrometric solutions for individual stars, an estimate of the
internal velocity dispersion in the cluster, and, where relevant, the effects
of the depth of the cluster along the line of sight. Internal consistency of
the TGAS data is assessed. . Values given for standard uncertainties are still
inaccurate and may lead to unrealistic unit-weight standard deviations of
least squares solutions for cluster parameters. Reconstructed mean cluster
parallax and proper motion values are generally in very good agreement with
earlier Hipparcos-based determination, although the Gaia mean parallax for the
Pleiades is a significant exception. We have no current explanation for that
discrepancy. Most clusters are observed to extend to nearly 15 pc from the
cluster centre, and it will be up to future Gaia releases to establish whether
those potential cluster-member stars are still dynamically bound to the
clusters. The Gaia DR1 provides the means to examine open clusters far beyond
their more easily visible cores, and can provide membership assessments based
on proper motions and parallaxes. A combined HR diagram shows the same
features as observed before using the Hipparcos data, with clearly increased
luminosities for older A and F dwarfs.

Waveband Coverage:
---------------------------------------------  

Spectroscopic survey of youngest field stars II.
Short Name: J/A+A/612/A96
IVOA Identifier: ivo://cds.vizier/j/a+a/612/a96
Access modes: tap#aux
Multi-capability service -- use get_service()

Star formation in the solar neighborhood is mainly traced by young stars in
open clusters, associations, and in the field, which can be identified, for
example, by their X-ray emission. The determination of stellar parameters for
the optical counterparts of X-ray sources is crucial for a full
characterization of these stars. This work extends the spectroscopic study of
the RasTyc sample, obtained by the cross-correlation of the TYCHO and ROSAT
All-Sky Survey catalogs, to stars fainter than V=9.5mag and aims to identify
sparse populations of young stars in the solar neighborhood. We acquired 625
high-resolution spectra for 443 presumably young stars with four different
instruments in the northern hemisphere. The radial and rotational velocity
(vsini) of our targets were measured by means of the cross-correlation
technique, which is also helpful to discover single-lined (SB1), double-lined
spectroscopic binaries (SB2), and multiple systems. We used the code ROTFIT to
perform an MK spectral classification and to determine the atmospheric
parameters (Teff, logg, [Fe/H]) and and vsini of the single stars and SB1
systems. For these objects, we used the spectral subtraction of slowly
rotating templates to measure the equivalent widths of the H{alpha} and
LiI-6708A lines, which enabled us to derive their chromospheric activity level
and lithium abundance. We made use of Gaia DR1 parallaxes and proper motions
to locate the targets in the HR diagram and to compute the space velocity
components of the youngest objects. We find a remarkable percentage (at least
35%) of binaries and multiple systems. On the basis of the lithium abundance,
the sample of single stars and SB1 systems appears to be mostly (about 60%)
composed of stars younger than the members of the UMa cluster. The remaining
sources are in the age range between the UMa and Hyades clusters (about 20%)
or older (20%). In total, we identify 42 very young (PMS-like) stars, which
lie above or very close to the Pleiades upper envelope of the lithium
abundance. A significant percentage (about 12%) of evolved stars (giants and
subgiants) is also present in our sample. Some of these stars are also lithium
rich (A(Li)>1.4).

Waveband Coverage: x-ray
---------------------------------------------  

Lithium content for 148 Pleiades stars
Short Name: J/A+A/613/A63
IVOA Identifier: ivo://cds.vizier/j/a+a/613/a63
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

The evolution of lithium abundance over a star's lifetime is indicative of
transport processes operating in the stellar interior. Aims. We revisit the
relationship between lithium content and rotation rate previously reported for
cool dwarfs in the Pleiades cluster. Methods. We derive new LiI 670.8nm
equivalent width measurements from high-resolution spectra obtained for low-
mass Pleiades members. We combine these new measurements with previously
published ones, and use the Kepler/K2 rotational periods recently derived for
Pleiades cool dwarfs to investigate the lithium-rotation connection in this
125Myr-old cluster. Results. The new data confirm the correlation between
lithium equivalent width and stellar spin rate for a sample of 51 early K-type
members of the cluster, where fast rotating stars are systematically lithium-
rich compared to slowly rotating ones. The correlation is valid for all stars
over the (J-Ks) color range 0.50-0.70mag, corresponding to a mass range from
about 0.75 to 0.90M_{sun}_, and may extend down to lower masses. Conclusions.
We argue that the dispersion in lithium equivalent widths observed for cool
dwarfs in the Pleiades cluster reflects an intrinsic scatter in lithium
abundances, and suggest that the physical origin of the lithium dispersion
pattern is to be found in the pre-main sequence rotational history of solar-
type stars.

Waveband Coverage:
---------------------------------------------  

Spectroscopic membership for NGC 3532
Short Name: J/A+A/622/A110
IVOA Identifier: ivo://cds.vizier/j/a+a/622/a110
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

NGC 3532 is an extremely rich open cluster embedded in the Galactic disc,
hitherto lacking a comprehensive, documented membership list. We provide
membership probabilities from new radial velocity observations of solar-type
and low-mass stars in NGC 3532, in part as a prelude to a subsequent study of
stellar rotation in the cluster. Using extant optical and infra-red photometry
we constructed a preliminary photometric membership catalogue, consisting of
2230 dwarf and turn-off stars. We selected 1060 of these for observation with
the AAOmega spectrograph at the 3.9m Anglo-Australian Telescope and 391 stars
for observations with the Hydra-South spectrograph at the 4m Victor Blanco
Telescope, obtaining spectroscopic observations over a decade for 145 stars.
We measured radial velocities for our targets through cross-correlation with
model spectra and standard stars, and supplemented them with radial velocities
for 433 additional stars from the literature. We also measured logg, Teff, and
[Fe/H] from the AAOmega spectra. The radial velocity distribution emerging
from the observations is centred at 5.43+/-0.04km/s and has a width (standard
deviation) of 1.46km/s. Together with proper motions from Gaia DR2 we find 660
exclusive members, of which five are likely binary members. The members are
distributed across the whole cluster sequence, from giant stars to M dwarfs,
making NGC~3532 one of the richest Galactic open clusters known to date, on
par with the Pleiades. From further spectroscopic analysis of 153 dwarf
members we find the metallicity to be marginally sub-solar, with
[Fe/H]=-0.07+/-0.10. We confirm the extremely low reddening of the cluster,
E_B-V_=0.034+/-0.012mag, despite its location near the Galactic plane.
Exploiting trigonometric parallax measurements from Gaia DR2 we find a
distance of 484^+35^_-30_pc [(m-M)_0_=8.42+/-0.14mag]. Based on the membership
we provide an empirical cluster sequence in multiple photometric passbands. A
comparison of the photometry of the measured cluster members with several
recent model isochrones enables us to confirm the 300Myr cluster age. However,
all of the models evince departures from the cluster sequence in particular
regions, especially in the lower mass range.

Waveband Coverage: infrared, optical
---------------------------------------------  

alpha Persei, Pleiades and Praesepe clusters
Short Name: J/A+A/628/A66
IVOA Identifier: ivo://cds.vizier/j/a+a/628/a66
Access modes: tap#aux
Multi-capability service -- use get_service()

Our scientific goal is to provide revised membership lists of the alpha Per,
Pleiades, and Praesepe clusters exploiting the second data release of Gaia and
produce five-dimensional maps ({alpha}, {delta}, {pi},
{mu}_{alpha}_cos{delta}, {mu}_{delta}_) of these clusters. We implemented the
kinematic method combined with the statistical treatment of parallaxes and
proper motions to identify astrometric member candidates of three of the most
nearby and best studied open clusters in the sky. We cross-correlated the Gaia
catalogue with large-scale public surveys to complement the astrometry of Gaia
with multi-band photometry from the optical to the mid-infrared. We identified
517, 1248, and 721 bona fide astrometric member candidates inside the tidal
radius of alpha Per, the Pleiades, and Praesepe, respectively. We cross-
matched our final samples with catalogues from previous surveys to address the
level of completeness. We update the main physical properties of the clusters,
including mean distance and velocity, as well as core, half-mass, and tidal
radii. We infer updated ages from the white dwarf members of the Pleiades and
Praesepe. We derive the luminosity and mass functions of the three clusters
and compare them to the field mass function. We compute the positions in space
of all member candidates in the three regions to investigate their
distribution in space. We provide updated distances and kinematics for the
three clusters. We identify a list of members in the alpha Per, Pleiades, and
Praesepe clusters from the most massive stars all the way down to the
hydrogen-burning limit with a higher confidence and better astrometry than
previous studies. We produce complete 5D maps of stellar and substellar bona
fide members in these three regions. The photometric sequences derived in
several colour-magnitude diagrams represent benchmark cluster sequences at
ages from 90 to 600Myr. We note the presence of a stream around the Pleiades
cluster extending up to 40 pc from the cluster centre.

Waveband Coverage:
---------------------------------------------  

A census of the near-by Psc-Eri stellar stream
Short Name: J/A+A/638/A9
IVOA Identifier: ivo://cds.vizier/j/a+a/638/a9
Access modes: tap#aux
Multi-capability service -- use get_service()

Within a sphere of 400pc radius around the Sun, we search for members of the
Pisces-Eridanus (Psc-Eri) stellar stream in the Gaia Data Release 2 DR2) data
set. We compare basic astrophysical characteristics of the stream with those
of the Pleiades. We used a modified convergent-point method to identify stars
with 2D - velocities consistent with the space velocity of the Psc-Eri stream
and the Pleiades, respectively. We found 1387 members of the Psc-Eri stream in
a G-magnitude range from 5.1mag to 19.3mag at distances between 80 and 380pc
from the Sun. The stream has a nearly cylindrical shape with a length of at
least 700pc and a thickness of 100pc. The accumulated stellar mass of the 1387
members amounts to about 770M_{sun}_, and the stream is gravitationally
unbound. For the stream we found an age of about 135Myr. In many astrophysical
properties Psc-Eri is comparable to the open cluster M45 (the Pleiades): in
its age, its luminosity function (LF), its present-day mass function (PDMF) as
well as in its total mass. Nonetheless, the two stellar ensembles are
completely unlike in their physical appearance. We cautiously give two
possible explanations for this disagreement: (i) the star-formation efficiency
in their parental molecular clouds was higher for the Pleiades than for Psc-
Eri or/and (ii) the Pleiades had a higher primordial mass segregation
immediately after the expulsion of the molecular gas of the parental cloud.

Waveband Coverage:
---------------------------------------------  

IC 4665 multi-band photometry
Short Name: J/A+A/641/A156
IVOA Identifier: ivo://cds.vizier/j/a+a/641/a156
Access modes: tap#aux
Multi-capability service -- use get_service()

Debris discs orbiting young stars are key to understand dust evolution and the
planetary formation process.We take advantage of a recent membership analysis
of the 30Myr nearby open cluster IC 4665 based on the Gaia and DANCe surveys
to revisit the disc population of this cluster. We aim to study the disc
population of IC 4665 using Spitzer (MIPS and IRAC) and WISE photometry. We
use several colour-colour diagrams with empirical photospheric sequences to
detect the sources with an infrared excess. Independently, we also fit the
spectral energy distribution (SED) of our debris disc candidates with the
Virtual Observatory SED analyser (VOSA) which is capable of automatically
detecting infrared excesses and provides effective temperature estimates. We
find six candidates debris disc host-stars (five with MIPS and one with WISE)
and two of them are new candidates. We estimate a disc fraction of 24+/-10%
for the B-A stars, where our sample is expected to be complete. This is
similar to what has been reported in other clusters of similar ages (Upper
Centaurus Lupus, Lower Centaurus Crux, the \beta Pictoris moving group, and
the Pleiades). For solar type stars we find a disk fraction of 9+/-9%, lower
than that observed in regions with comparable ages. Our candidates debris disc
host-stars are excellent targets to be studied with ALMA or the future James
Webb Space Telescope (JWST).

Waveband Coverage: optical, infrared
---------------------------------------------  

NGC 2516 membership list
Short Name: J/A+A/641/A51
IVOA Identifier: ivo://cds.vizier/j/a+a/641/a51
Access modes: tap#aux
Multi-capability service -- use get_service()

We wish to measure the cool star rotation period distribution for the
Pleiades-age rich open cluster NGC 2516 and use it to determine whether
cluster-to-cluster variations exist in otherwise identical open clusters. We
obtained 42d-long time-series CCD photometry of NGC 2516 in the V and Ic
filters using the Yale 1m telescope at CTIO and performed a number of related
analyses, including PSF-based time-series photometry. Our data are
complemented with additional information from several photometric datasets,
literature radial velocities, and Gaia DR2 astrometry. All available data are
used to construct an integrated membership list for NGC 2516, containing 844
stars in our ~1 degree field of view. We derived 308 rotation periods for
late-F to mid-M cluster members from our photometry. We identified an
additional 247 periodic M dwarf stars from a prior study as cluster members,
and used these to construct a 555-star rotation period distribution for NGC
2516. The colour-period diagram (in multiple colours) has almost no outliers
and exhibits the anticipated triangular shape, with a diagonal slow rotator
sequence that is preferentially occupied by the warmer stars along with a flat
fast rotator sequence that is preferentially populated by the cooler cluster
members. We also find a group of extremely slowly rotating M dwarfs
(10d<P<23d), forming a branch in the colour-period diagram which we call the
'extended slow rotator sequence'. This, and other features of the rotational
distribution can also be found in the Pleiades, making the colour-period
diagrams of the two clusters nearly indistinguishable. A comparison with the
well-studied (and similarly aged) open cluster M 35 indicates that the
cluster's rotational distribution is also similarly indistinguishable from
that of NGC 2516. Those for the open clusters M 50 and Blanco 1 are similar,
but data issues for those clusters make the comparisons somewhat more
ambiguous. Nevertheless, we demonstrate the existence of a representative
zero-age main sequence (ZAMS) rotational distribution and provide a simple
colour-independent way to represent it. We perform a detailed comparison of
the NGC 2516 rotation period data with a number of recent rotational evolution
models. Using X-ray data from the literature, we also construct the first
rotation-activity diagram for solar-type stars in NGC 2516, one that we find
is essentially indistinguishable from those for the Pleiades and Blanco 1. The
two clusters NGC 2516 and Pleiades can be considered twins in terms of stellar
rotation and related properties (and M 35, M 50, and Blanco 1 are similar),
suggesting that otherwise identical open clusters also have intrinsically
similar cool star rotation and activity distributions.

Waveband Coverage:
---------------------------------------------  

Rotation periods for NGC 3532
Short Name: J/A+A/652/A60
IVOA Identifier: ivo://cds.vizier/j/a+a/652/a60
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

A very rich cluster intermediate in age between the Pleiades (150Myr) and the
Hyades (600Myr) is needed to probe the rotational evolution, especially the
transition between fast and slow rotation that occurs between the two ages. We
study the rich 300Myr-old open cluster NGC 3532 to probe this important
transition and to provide constraints on angular momentum loss. Measuring the
rotation periods builds on our prior work of providing spectroscopic
membership information for the cluster, and it supports the chromospheric
activity measurements of cluster stars that we provide in a companion paper.
Using 42d-long photometric time series observations obtained with the Yale 1m
telescope at CTIO, we measured rotation periods for members of NGC 3532 and
compared them with the predictions of angular momentum evolution models. We
directly measured 176 photometric rotation periods for the cluster members. An
additional 113 photometric rotation periods were identified using activity
information, described fully in the companion paper, resulting in a total
sample containing 279 rotation periods for FGKM stars in NGC 3532. The colour-
period diagram constructed from this rich data set shows a well-populated and
structured slow rotator sequence, and a fast rotator sequence evolved beyond
zero-age main sequence age whose stars are in transition from fast to slow
rotation. The slow rotator sequence itself is split into slightly slower and
faster rotators, a feature we trace to photometric binary status. We also
identify an extended slow rotator sequence extending to P~32d, apparently the
analogue of the one we previously identified in NGC 2516. We compare our
period distribution to rotational isochrones in colour-period space and find
that all considered models have certain shortcomings. Using more detailed
spin-down models, we evolve the rotation periods of the younger NGC 2516
forward in time and find that the spindown of the models is too aggressive
with respect to the slow rotators. In contrast, stars on the evolved fast
rotator sequence are not spun down strongly enough by these models. Our
observations suggest a shorter crossing time for the rotational gap, one we
estimate to be ~80Myr for early-K dwarfs.

Waveband Coverage:
---------------------------------------------  

Rotation periods of Group X candidate members
Short Name: J/A+A/657/L3
IVOA Identifier: ivo://cds.vizier/j/a+a/657/l3
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

Gyrochronology is one of the methods currently used to estimate the age of
stellar open clusters. Hundreds of new clusters, associations, and moving
groups unveiled by Gaia and complemented by accurate rotation period
measurements provided by recent space missions such as Kepler and TESS are
allowing us to significantly improve the reliability of this method. Aims. We
use gyrochronology, that is, the calibrated age-mass-rotation relation valid
for low-mass stars, to measure the age of the recently discovered moving group
Group X. We extracted the light curves of all candidate members from the TESS
full frame images and measured their rotation periods using different period
search methods. Results. We measured the rotation period of 168 of a total of
218 stars and compared their period-colour distribution with those of two age-
benchmark clusters, the Pleiades (125Myr) and Praesepe (625Myr), as well as
with the recently characterised open cluster NGC 3532 (300Myr). As result of
our analysis, we derived a gyro age of 300+/-60Myr. We also applied as
independent methods the fitting of the entire isochrone and of the three
brightest candidate members individually with the most precise stellar
parameters, deriving comparable values of 250 Myr and 290 Myr, respectively.
Our dating of Group X allows us to definitively rule out the previously
proposed connection with the nearby but much older Coma Berenices cluster.

Waveband Coverage:
---------------------------------------------  

NGC 6709 cool stars rotation periods
Short Name: J/A+A/673/A119
IVOA Identifier: ivo://cds.vizier/j/a+a/673/a119
Access modes: tap#aux
Multi-capability service -- use get_service()

Open clusters serve as a useful tool for calibrating models of the
relationship between mass, rotation, and age for stars with an outer
convection zone due to the homogeneity of the stars within the cluster.
Cluster to cluster comparisons are essential to determine whether the
universality of spin-down relations holds. NGC 6709 is chosen as a more
distant representative Pleiades-age cluster for which no rotation periods of
members have previously been obtained. This cluster is at a distance of over 1
kpc and has two red giant members. Isochrones place the age of the cluster at
around 150Myr, or approximately the same age as the Pleiades. Photometry is
obtained over a multi-month observing season at the robotic observatory for
STELLar Activity (STELLA). After basic processing, point- spread function
photometry was derived using Daophot II, and a suite of related software
allowed us to create time series of relative magnitude changes for each star.
Four time series analysis methods are then applied to these light curves to
obtain rotation periods for members stars. We obtain for the first time
rotation periods for 45 FGK cluster members of NGC 6709. We plot the Gaia DR3
colors of the member stars against their rotation periods and find a slow-
rotating sequence with increasing rotation periods towards redder stars and a
smaller clump of rapid rotators that have not yet joined this sequence. NGC
6709 has rotation periods very similar to that of another Pleiades-age open
cluster, NGC 2516.

Waveband Coverage: optical
---------------------------------------------  

Pleiades bonafide single stars
Short Name: J/A+A/677/A162
IVOA Identifier: ivo://cds.vizier/j/a+a/677/a162
Access modes: tap#aux
Multi-capability service -- use get_service()

The Gaia astrophysical parameters inference system (Apsis) provides
astrophysical parameter estimates for several to hundreds of millions of
stars. Aims. We aim to benchmark Gaia DR3 Apsis. We compiled approximately
1500 bona fide single stars in the Hyades and Pleiades open clusters for
validation of PARSEC isochrones, and for comparison with Apsis estimates.
PARSEC stellar isochrones in the Gaia photometric system enable us to assign
average ages and metallicities to the clusters, and mass, effective
temperature, luminosity, and surface gravity to the individual stars. Apsis
does not recover the single-age, single-metallicity characteristic of the
cluster populations. Ages assigned to cluster members seemingly follow the
input template for Galactic populations, with earlier-type stars being
systematically assigned younger ages than later-type stars. Cluster
metallicities are underestimated by 0.1 to 0.2dex. Effective temperature
estimates are in general reliable. Surface gravity estimates reveal strong
systematic errors for specific ranges of the Gaia BP-RP colours. We caution
that Gaia DR3 Apsis estimates can be subject to significant systematic
uncertainties. Some of the Apsis estimates, such as metallicity, might only be
meaningful for statistical studies of the time-averaged Galactic stellar
population, but are not recommended to be used for individual stars.

Waveband Coverage: optical
---------------------------------------------  

Young nearby open clusters members photometry
Short Name: J/A+A/678/A75
IVOA Identifier: ivo://cds.vizier/j/a+a/678/a75
Access modes: tap#aux
Multi-capability service -- use get_service()

Open clusters are groups of coeval stars sharing properties such as distance
and metallicity, and they are key to understanding stellar evolution. Our main
goal is to study the evolution of open clusters with a special focus on the
universality of the luminosity function. We applied an upgraded version of the
convergent point technique on about 50 open clusters. The selection of cluster
members was based purely on the exquisite astrometry of the Gaia DR3 and
Hipparcos catalogues in the five-dimensional or full six-dimensional space. We
present updated lists of bona fide members of ~50 open clusters within 500pc
and younger than 1Gyr, exploiting the full depth of the third Gaia data
release complemented by Hipparcos at the bright end, excluding regions in the
Galactic plane. Our catalogues also are complemented by optical and infrared
photometry from the major large-scale public surveys. All the data will be
made available on a dedicated webpage with interactive plots and a direct link
to Aladin and Vizier hosted at the Centre de Donnees de Strasbourg. We derived
luminosity functions for all bound clusters and compared them in three age
groups of ~50Myr, ~150Myr, and ~600Myr, discussing similarities and
differences to constrain their dynamical evolution. Luminosity functions of
clusters at 50Myr are more likely similar to each other and show a greater
degree of similarity than older clusters. We explain this observation with the
universal luminosity function within the volume of our sample (500pc).
Luminosity functions of clusters with ages similar to the Pleiades or Hyades
are more diverse, perhaps due to internal dynamical evolution, but more work
is needed to provide additional evidence.

Waveband Coverage: optical, infrared
---------------------------------------------  

Very low mass proper motion members in Pleiades
Short Name: J/A+AS/100/607
IVOA Identifier: ivo://cds.vizier/j/a+as/100/607
Access modes: tap#aux
Multi-capability service -- use get_service()

A proper motion membership list is presented for the lower mass stars in the
Pleiades open cluster based on a survey of about a 5x5{deg} area around the
cluster center. Finder charts prepared from an R passband Schmidt plate are
given. Photographic R and I photometry is given for all stars; where possible
a V magnitude is also listed. The photometry is accurate to about 0.1mag.

Waveband Coverage: optical
---------------------------------------------  

BV photometry of Blanco 1 stars
Short Name: J/A+AS/121/213
IVOA Identifier: ivo://cds.vizier/j/a+as/121/213
Access modes: tap#aux
Multi-capability service -- use get_service()

We present the results of H{alpha}(6562A) and Li I(6708A) observations of 114
low-mass stars of the young open cluster Blanco 1. We also present
observations of 30 stars in Ca II(K). This work extends the first Blanco 1
spectroscopic study of Panagi et al. (1994A&A...285..233D). From a sample of
four well-studied clusters, including Blanco 1, we find that the fraction of
H{alpha} emission-line stars amongst K dwarfs is a good indicator of relative
age, with a smaller fraction indicative of older age. Blanco 1 shows a
relatively small fraction of emitters, inconsistent with previous age
estimates for the cluster. We estimate the cluster age to to be 90+/-25Myr,
slightly older than the Pleiades. The method is shown to be more sensitive to
age than lithium and a useful alternative to other age measurement techniques.
The variation of H{alpha} with (B-V) is similar to that observed in the older
solar neighbourhood dwarfs, suggesting that, at least for the absorption-line
stars, the contribution of stellar rotation to the equivalent width is
unclear. We combine both spectroscopy and photometry to revise cluster
membership and give accurate positions for all these stars.

Waveband Coverage: optical
---------------------------------------------  

Members of IC 2391
Short Name: J/A+AS/126/357
IVOA Identifier: ivo://cds.vizier/j/a+as/126/357
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

New 4-colour BV(RI)_KC_ CCD photometry to a limiting magnitude of V=~19 is
presented for 1428 objects observed towards the direction of the young, open
cluster IC 2391. We observed 36 (2'x3') fields within 17arcmin of the nominal
cluster core. By fitting the theoretical isochrones of D'Antona & Mazzitelli
(1994ApJS...90..467D) to a combination of colour-magnitude and colour-colour
diagrams, we have identified 17 stars as probable cluster members with a
further 85 stars as possible members. The brightness distribution of low-mass
members is compared with the luminosity function observed for the Pleiades and
we estimate that the contamination due to background giants should be small.

Waveband Coverage: optical, infrared
---------------------------------------------  

New weak-line T Tauri stars in Taurus-Auriga
Short Name: J/A+AS/132/173
IVOA Identifier: ivo://cds.vizier/j/a+as/132/173
Access modes: tap#aux
Multi-capability service -- use get_service()

We present results of an extensive search for weak-line T Tauri stars (WTTS)
in the outskirts of the Taurus-Auriga molecular cloud on the basis of the
ROSAT All-Sky Survey Bright Source Catalog (Cat. <IX/10>). Our surveyed region
extends from 2h 40m to 5h 40m in right ascension and from 10deg to 40deg in
declination, with the central part of Taurus-Auriga(4h<{alpha}<5h,
15deg<{delta}<34deg), accomplished by Wichmann et al. (1996, Cat.
<J/A+A/312/439>), excluded. Within a sky coverage of about 10^{3} square
degrees, 219 X-ray sources fullfill the criteria for selecting program sources
suggested by Neuhauser et al. (1995A&A...295L...5N) and 164 of these X-ray
sources were found to have at least one optical counterpart with E magnitude
brighter than 16. Low-resolution spectroscopic observation has been carried
out in order to discard early type stars and galaxies from the sample,
additional intermediate-resolution spectra of a sub-sample of 156 late type
optical counterparts were obtained for spectral classification and for the
calculation of the equivalent width of H{alpha} emission and LiI line
absorption at 6707{AA}. Excluding 2 previously identified WTTS, a total of 75
new candidate WTTS and one possible classical T Tauri star have been
discovered in our study. The majority of the newly found Li-rich optical
counterparts are believed to b e PMS stars rather than ZAMS stars as those of
the Pleiades.

Waveband Coverage: x-ray
---------------------------------------------  

Blue horizontal branch stars
Short Name: J/AJ/108/1722
IVOA Identifier: ivo://cds.vizier/j/aj/108/1722
Access modes: tap#aux
Multi-capability service -- use get_service()

A complete sample of blue horizontal branch (BHB) stars in the magnitude range
13.0<V<16.5 is isolated in two Galactic fields that have previously been
searched for RR Lyrae variables: SA 57 in the Northern Polar Cap and the Lick
Astrograph field RR 7 in the Anticenter (l=183{deg}, b=+37{deg}). These BHB
stars are a subset of the AF stars found in the Case Low-Dispersion Northern
Survey; lists of these AF stars were made available by the late Nick
Sanduleak. The completeness of the sample was confirmed by reference to the
photometric survey of SA 57 by Stobie & Ishida (1987AJ93..... 624S) that is
complete to fainter than V=18. In the color range 0.00<(B-V)_0_<+0.20, we can
distinguish the BHB stars among these AF stars by comparing them both with
well known local field horizontal branch (FHB) stars and also the BHB members
of the halo globular clusters M3 and M92. The criteria for this comparison
include (1) a (u-B)_K_ color index (derived from photoelectric observations
using the Stromgren u filter and the Johnson B and V filters) that measures
the size of the Balmer jump, (2) a spectrophotometric index A that measures
the steepness of the Balmer jump, and (3) a parameter D_0.2_ that is the mean
width of the H{gamma} and H{delta} Balmer lines measured at 20 percent of the
continuum level. These criteria give consistent results in separating BHB
stars from higher gravity main sequence AF stars in the color range
0.00<(B-V)_0_<+0.20. All three photometric and spectrophotometric criteria
were measured for 35 stars in the SA 57 field and 37 stars in the RR 7 field
that are in the color range (B-V)_0_<+0.23 and in the magnitude range
13.0<V<16.5. For a small number of additional stars only (u-B)_K_ was
obtained. Among the AF stars that are fainter than B=13 and bluer than
(B-V)_0_=+0.23, about half of those in the SA 57 field and about one third of
those in the lower latitude RR 7 field are BHB stars. Isoabundance contours
were located empirically in plots of the pseudoequivalent width versus
(B-V)_0_ for the lines of Mg II A4481{AA}, Ca II A3933 {AA} and Fe I
A4272{AA}. Solar abundances were defined by the data from main sequence stars
in the Pleiades and Coma open clusters. Data from the BHB stars in M3 and M92
defined the [Fe/H]=1.5 and -2.2 isoabundance contours, respectively.
Metallicities of all stars were estimated by interpolating the measured
pseudoequivalent widths in these diagrams at the observed (B-V)_0_. The
distribution of [Fe/H] found for the BHB stars in this way is very similar to
that which we found for the RR Lyrae stars in the same fields using the
Preston AS method. The space densities of these BHB stars were analyzed both
separately and together with earlier observations of field BHB stars given by
Arnold & Gilmore (1992MNRAS.257..225A), Sommer-Larsen & Christensen
(1986MNRAS.219..537S), and Preston et al. (1991ApJ...375..121P). This analysis
supports a two-component model for the halo of our Galaxy that is similar in
many respects to that proposed by Hartwick [The Galaxy (Reidel, Dordrecht
1987)] although our discussion refers only to the region outside the solar
circle. For Z>=35kpc, a classical spherical halo dominates which follows a
R_gal_^-3.5^ space-density law and which has a HB morphology like that of the
globular cluster M3 (i.e., approximately equal numbers of BHB and RR Lyrae
stars). Closer to the galactic plane, there is an additional component with a
much flatter galactic distribution (scale height ~2.2kpc near the Sun). The
stars of the two components do not have significantly different metallicity
distributions but do have slightly different distributions of the A parameter
which measures the steepness of the Balmer jump; this is the only physical
criterion (independent of spatial or kinematic considerations) which
distinguishes between the two components. If present estimates of the local RR
Lyrae star space density are correct, then the ratio of BHB stars to RR Lyrae
stars is higher in the flatter halo component. The flat component would then
have a bluer HB morphology (which could be interpreted as making it older)
than the spherical component. In the solar neighborhood about 80 percent of
the BHB stars come from the flat component and about 20 percent from the
spherical component. More than half of the AF stars with V>13.0 and
(B-V)_0_<+0.23 are not BHB stars but have surface gravities that are more like
those expected for main sequence stars. Their measured metallicities lie in
the range -0.2<[Fe/H]<-2.3. The more metal-poor of these stars are probably
similar to the blue metal-poor stars that have been discussed by Preston et
al. (1994AJ....108..538P) which, while they probably include globular cluster
blue stragglers as a subset, must also comprise stars of other types.

Waveband Coverage: optical
---------------------------------------------  

ROSAT X-ray survey in NGC 6475
Short Name: J/AJ/110/1229
IVOA Identifier: ivo://cds.vizier/j/aj/110/1229
Access modes: tap#aux
Multi-capability service -- use get_service()

A ROSAT X-ray survey, with complementary optical photometry, of the open
cluster NGC 6475 has enabled the detection of ~50 late-F to K0 and ~70 K/M
dwarf new candidate members, providing the first reliable detection of low-
mass stars in this low galactic latitude, 220Myr old cluster. The X-ray
observations reported here have a typical limiting sensitivity of L_X_ ~
10^29^erg/s. The detection frequency of early type cluster members is
consistent with the hypothesis that the X-ray emitting early type stars are
binary systems with an unseen, low-mass secondary producing the X-rays. The
ratio between X-ray and bolometric luminosity among NGC 6475 members saturates
at a spectral-type/color which is intermediate between that in much younger
and in much older clusters, consistent with rotational spindown of solar-type
stars upon their arrival on the ZAMS. The upper envelope of X-ray luminosity
as a function of spectral type is comparable to that of the Pleiades, with the
observed spread in X-ray luminosity among low-mass members being likely due to
the presence of binaries and relatively rapid rotators. However, the list of
X-ray selected candidate members is likely biased against low-mass, slowly
rotating single stars. While some preliminary spectroscopic information is
given in an appendix, further spectroscopic observations of the new candidate
members will aid in interpreting the coronal activity among solar-type NGC
6475 members and their relation to similar stars in older and younger open
clusters.

Waveband Coverage: x-ray
---------------------------------------------  

Spectrophotometry in open clusters
Short Name: J/AJ/114/699
IVOA Identifier: ivo://cds.vizier/j/aj/114/699
Access modes: tap#aux
Multi-capability service -- use get_service()

Spectrophotometry is presented for 237 stars in 7 nearby open clusters:
Hyades, Pleiades, Alpha Persei, Praesepe, Coma Berenices, IC 4665, and M39.
The observations were taken by Lee McDonald and David Burstein using the
Wampler single-channel scanner on the Crossley 0.9m telescope at Lick
Observatory from 1973 July through 1974 December. Sixteen bandpasses spanning
the spectral range 3500-7780{AA} were observed for each star, with bandwidths
32, 48, or 64{AA}. Data are standardized to the Hayes-Latham system to mutual
accuracy of 0.016mag per passband. The accuracy of the spectrophotometry is
assessed in three ways on a star-by-star basis. First, comparisons are made
with previously published spectrophotometry for 19 stars observed in common.
Second, (B-V) colors and uvby colors are compared for 236 stars and 221 stars,
respectively. Finally, comparisons are made for 200 main sequence stars to the
spectral synthesis models of Kurucz, fixing logg=4.0 and [Fe/H]=0.0, and only
varying effective temperature. The accuracy of tests using uvby colors and the
Kurucz models are shown to track each other closely, yielding an accuracy
estimate (1{sigma}) of 0.01mag for the 13 colors formed from bandpasses
longward of the Balmer jump, and 0.02mag for the 3 colors formed from the
three bandpasses below the Balmer jump. In contrast, larger scatter is found
relative to the previously published spectrophotometry of Bohm-Vitense &
Johnson (1977ApJS...35..461B) (16 stars in common) and Gunn & Stryker (1983,
Cat. <III/88>) (3 stars). We also show that the scatter in the fits of the
spectrophotometric colors and the uvby filter colors is a reasonable way to
identify the observations of which specific stars are accurate to 1{sigma},
2{sigma}, .... As such, the residuals from both the filter color fits and the
Kurucz model fits are tabulated for each star where it was possible to make a
comparison, so users of these data can choose stars according to the accuracy
of the data that is appropriate to their needs. The very good agreement
between the models and these data verifies the accuracy of these data, and
also verifies the usefulness of the Kurucz models to define spectrophotometry
for stars in this temperature range (>5000K). These data define accurate
spectrophotometry of bright, open cluster stars that can be used as a
secondary flux calibration for CCD-based spectrophotometric surveys. (c) 1997
American Astronomical Society.

Waveband Coverage: optical
---------------------------------------------  

Rotation periods of Orion PMS stars
Short Name: J/AJ/117/2941
IVOA Identifier: ivo://cds.vizier/j/aj/117/2941
Access modes: tap#aux
Multi-capability service -- use get_service()

We report rotation periods for 254 stars in an area 40'x80' centered on the
Orion Nebula. We show that these stars are likely members of the young
(~10^6^yr) Orion OBIc/d association. The rotation period distribution we
determine, which is sensitive to periods 0.1<P<8days, shows a sharp cutoff for
periods P<0.5days, corresponding to breakup velocity for these stars. Above
0.5days the distribution is consistent with a uniform distribution; we do not
find evidence for a "gap" of periods at 4-5days. We find signatures of active
accretion among stars at all periods; active accretion does not occur
preferentially among slow rotators in our sample. We find no correlation
between rotation period and near-IR signatures of circumstellar disks. In
addition, we show that the distribution of vsini among stars in our sample
bears striking resemblance to that of low-mass Pleiades stars. We discuss the
implications of our findings for the evolution of stellar angular momentum
during the pre-main-sequence phase. We argue that all stars in our sample must
still deplete angular momentum by factors of roughly 5-10, if they are to
preserve their vsini distribution over approximately the next 100Myr. We
consider in detail whether our findings are consistent with disk-regulated
stellar rotation. We do not find observational evidence that magnetic disk-
locking is the dominant mechanism in angular momentum evolution during the
premain-sequence phase.

Waveband Coverage: optical
---------------------------------------------  

BVI photometry of 350 Pleiades stars
Short Name: J/AJ/148/30
IVOA Identifier: ivo://cds.vizier/j/aj/148/30
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

We present new BVI_C_ photometry for 350 Pleiades proper motion members with
9<V<~17. Importantly, our new catalog includes a large number of K- and early
M-type stars, roughly doubling the number of low-mass stars with well-
calibrated Johnson/Cousins photometry in this benchmark cluster. We combine
our new photometry with existing photometry from the literature to define a
purely empirical isochrone at Pleiades age ({approx}100Myr) extending from V=9
to 17. We use the empirical isochrone to identify 48 new probable binaries and
14 likely nonmembers. The photometrically identified single stars are compared
against their expected positions in the color-magnitude diagram (CMD). At
100Myr, the mid K and early M stars are predicted to lie above the zero-age
main sequence (ZAMS) having not yet reached the ZAMS. We find in the B-V
versus V CMD that mid K and early M dwarfs are instead displaced below (or
blueward of) the ZAMS. Using the stars' previously reported rotation periods,
we find a highly statistically significant correlation between rotation period
and CMD displacement, in the sense that the more rapidly rotating stars have
the largest displacements in the B-V CMD.

Waveband Coverage: infrared, optical
---------------------------------------------  

Pleiades members with K2 light curves. I. Periods
Short Name: J/AJ/152/113
IVOA Identifier: ivo://cds.vizier/j/aj/152/113
Access modes: tap#aux
Multi-capability service -- use get_service()

Young (125Myr), populous (>1000 members), and relatively nearby, the Pleiades
has provided an anchor for stellar angular momentum models for both younger
and older stars. We used K2 to explore the distribution of rotation periods in
the Pleiades. With more than 500 new periods for Pleiades members, we are
vastly expanding the number of Pleiades with periods, particularly at the low-
mass end. About 92% of the members in our sample have at least one measured
spot-modulated rotation period. For the ~8% of the members without periods,
non-astrophysical effects often dominate (saturation, etc.), such that
periodic signals might have been detectable, all other things being equal. We
now have an unusually complete view of the rotation distribution in the
Pleiades. The relationship between P and (V-K_s_)_0_ follows the overall
trends found in other Pleiades studies. There is a slowly rotating sequence
for 1.1<~(V-K_s_)_0_<~3.7 and a primarily rapidly rotating population for
(V-K_s_)_0_>~5.0. There is a region in which there seems to be a disorganized
relationship between P and (V-K_s_)_0_ for 3.7<~(V-K_s_)_0_<~5.0. Paper II
continues the discussion, focusing on multiperiod structures, and Paper III
speculates about the origin and evolution of the period distribution in the
Pleiades.

Waveband Coverage:
---------------------------------------------  

Pleiades members with K2 light curves. II.
Short Name: J/AJ/152/114
IVOA Identifier: ivo://cds.vizier/j/aj/152/114
Access modes: tap#aux
Multi-capability service -- use get_service()

We use K2 to continue the exploration of the distribution of rotation periods
in Pleiades that we began in Paper I. We have discovered complicated
multiperiod behavior in Pleiades stars using these K2 data, and we have
grouped them into categories, which are the focal part of this paper. About
24% of the sample has multiple, real frequencies in the periodogram, sometimes
manifesting as obvious beating in the LCs. Those having complex and/or
structured periodogram peaks, unresolved multiple periods, and resolved close
multiple periods are likely due to spot/spot group evolution and/or
latitudinal differential rotation; these largely compose the slowly rotating
sequence in P versus (V-K_s_)_0_ identified in Paper I. The fast sequence in P
versus (V-K_s_)_0_ is dominated by single-period stars; these are likely to be
rotating as solid bodies. Paper III continues the discussion, speculating
about the origin and evolution of the period distribution in the Pleiades.

Waveband Coverage:
---------------------------------------------  

Pleiades members with K2 light curves. III.
Short Name: J/AJ/152/115
IVOA Identifier: ivo://cds.vizier/j/aj/152/115
Access modes: tap#aux
Multi-capability service -- use get_service()

We use high-quality K2 light curves for hundreds of stars in the Pleiades to
better understand the angular momentum evolution and magnetic dynamos of young
low-mass stars. The K2 light curves provide not only rotational periods but
also detailed information from the shape of the phased light curve that was
not available in previous studies. A slowly rotating sequence begins at
(V-K_s_)_0_~1.1 (spectral type F5) and ends at (V-K_s_)_0_~3.7 (spectral type
K8), with periods rising from ~2 to ~11 days in that interval. A total of 52%
of the Pleiades members in that color interval have periods within 30% of a
curve defining the slow sequence; the slowly rotating fraction decreases
significantly redward of (V-K_s_)_0_=2.6. Nearly all of the slow-sequence
stars show light curves that evolve significantly on timescales less than the
K2 campaign duration. The majority of the FGK Pleiades members identified as
photometric binaries are relatively rapidly rotating, perhaps because binarity
inhibits star-disk angular momentum loss mechanisms during pre-main-sequence
evolution. The fully convective late M dwarf Pleiades members
(5.0<(V-K_s_)_0_<6.0) nearly always show stable light curves, with little spot
evolution or evidence of differential rotation. During pre-main-sequence
evolution from ~3Myr (NGC2264 age) to ~125Myr (Pleiades age), stars of
0.3M_{Sun}_ shed about half of their angular momentum, with the fractional
change in period between 3 and 125Myr being nearly independent of mass for
fully convective stars. Our data also suggest that very low mass binaries form
with rotation periods more similar to each other and faster than would be true
if drawn at random from the parent population of single stars.

Waveband Coverage:
---------------------------------------------  

Pleiades members stellar properties
Short Name: J/AJ/153/101
IVOA Identifier: ivo://cds.vizier/j/aj/153/101
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

Precise measurements of eclipsing binary parameters and statistical studies of
young clusters have suggested that some magnetically active low-mass dwarfs
possess radii inflated by ~5%-15% relative to theoretical expectations. If
true, this effect should be pronounced in young open clusters, due to the
rapid rotation and strong magnetic activity of their most extreme members. We
explore this possibility by determining empirical radii for 83 members of the
nearby Pleiades open cluster, using spectral energy distribution fitting to
establish F_bol_ with a typical accuracy of ~3% together with color and
spectro-photometric indices to determine T_eff_. We find several Pleiades
members with radii inflated above radius-T_eff_ models from state-of-the-art
calculations, and apparent dispersions in radii for the K-dwarfs of the
cluster. Moreover, we demonstrate that this putative radius inflation
correlates strongly with rotation rate, consistent with inflation of young
stars by magnetic activity and/or starspots. We argue that this signal is not
a consequence of starspot-induced color anomalies, binarity, or depth effects
in the cluster, employing Gaia DR1 distances as a check. Finally, we consider
the lithium abundances of these stars, demonstrating a triple correlation
between rotation rate, radius inflation, and enhanced lithium abundance. Our
result-already significant to ~99.99% confidence-provides strong support for a
magnetic origin of the inflated radii and lithium dispersion observed in
young, low-mass stars.

Waveband Coverage: optical, infrared
---------------------------------------------  

The solar neighborhood. XLII. New nearby subdwarfs
Short Name: J/AJ/154/191
IVOA Identifier: ivo://cds.vizier/j/aj/154/191
Access modes: tap#aux
Multi-capability service -- use get_service()

Parallaxes, proper motions, and optical photometry are presented for 51
systems consisting of 37 cool subdwarf and 14 additional high proper motion
systems. Thirty-seven systems have parallaxes reported for the first time, 15
of which have proper motions of at least 1"/yr. The sample includes 22 newly
identified cool subdwarfs within 100 pc, of which three are within 25 pc, and
an additional five subdwarfs from 100 to 160 pc. Two systems-LSR 1610-0040 AB
and LHS 440 AB-are close binaries exhibiting clear astrometric perturbations
that will ultimately provide important masses for cool subdwarfs. We use the
accurate parallaxes and proper motions provided here, combined with additional
data from our program and others, to determine that effectively all nearby
stars with tangential velocities greater than 200 km/s are subdwarfs. We
compare a sample of 167 confirmed cool subdwarfs to nearby main sequence
dwarfs and Pleiades members on an observational Hertzsprung-Russell diagram
using M_V_ versus (V-K_s_) to map trends of age and metallicity. We find that
subdwarfs are clearly separated for spectral types K5-M5, indicating that the
low metallicities of subdwarfs set them apart in the H-R diagram for
(V-K_s_)=3-6. We then apply the tangential velocity cutoff and the subdwarf
region of the H-R diagram to stars with parallaxes from Gaia Data Release 1
and the MEarth Project to identify a total of 29 new nearby subdwarf
candidates that fall clearly below the main sequence.

Waveband Coverage: optical, infrared
---------------------------------------------  

Transiting planets in young clusters from K2
Short Name: J/AJ/154/224
IVOA Identifier: ivo://cds.vizier/j/aj/154/224
Access modes: tap#aux
Multi-capability service -- use get_service()

Detection of transiting exoplanets around young stars is more difficult than
for older systems owing to increased stellar variability. Nine young open
cluster planets have been found in the K2 data, but no single analysis
pipeline identified all planets. We have developed a transit search pipeline
for young stars that uses a transit-shaped notch and quadratic continuum in a
12 or 24 hr window to fit both the stellar variability and the presence of a
transit. In addition, for the most rapid rotators (P_rot_<2 days) we model the
variability using a linear combination of observed rotations of each star. To
maximally exploit our new pipeline, we update the membership for four stellar
populations observed by K2 (Upper Scorpius, Pleiades, Hyades, Praesepe) and
conduct a uniform search of the members. We identify all known transiting
exoplanets in the clusters, 17 eclipsing binaries, one transiting planet
candidate orbiting a potential Pleiades member, and three orbiting unlikely
members of the young clusters. Limited injection recovery testing on the known
planet hosts indicates that for the older Praesepe systems we are sensitive to
additional exoplanets as small as 1-2 R_{Earth}_, and for the larger Upper
Scorpius planet host (K2-33) our pipeline is sensitive to ~4 R_{Earth}_
transiting planets. The lack of detected multiple systems in the young
clusters is consistent with the expected frequency from the original Kepler
sample, within our detection limits. With a robust pipeline that detects all
known planets in the young clusters, occurrence rate testing at young ages is
now possible.

Waveband Coverage: infrared, optical
---------------------------------------------  

Analysis of K2 LCs for members of USco & {rho} Oph
Short Name: J/AJ/155/196
IVOA Identifier: ivo://cds.vizier/j/aj/155/196
Access modes: tap#aux
Multi-capability service -- use get_service()

We present an analysis of K2 light curves (LCs) for candidate members of the
young Upper Sco (USco) association (~8 Myr) and the neighboring {rho} Oph
embedded cluster (~1 Myr). We establish ~1300 stars as probable members, ~80%
of which are periodic. The phased LCs have a variety of shapes which can be
attributed to physical causes ranging from stellar pulsation and stellar
rotation to disk-related phenomena. We identify and discuss a number of
observed behaviors. The periods are ~0.2-30 days with a peak near 2 days and
the rapid period end nearing breakup velocity. M stars in the young USco
region rotate systematically faster than GK stars, a pattern also present in
K2 data for the older Pleiades and Praesepe systems. At higher masses (types
FGK), the well-defined period-color relationship for slowly rotating stars
seen in the Pleiades and Praesepe systems is not yet present in USco.
Circumstellar disks are present predominantly among the more slowly rotating M
stars in USco, with few disks in the subday rotators. However, M dwarfs with
disks rotate faster on average than FGK systems with disks. For four of these
disked M dwarfs, we provide direct evidence for disk locking based on the K2
LC morphologies. Our preliminary analysis shows a relatively mass-independent
spin-up by a factor of ~3.5 between USco and the Pleiades, then mass-dependent
spin-down between Pleiades and Praesepe.

Waveband Coverage: optical, infrared
---------------------------------------------  

Robo-AO binary star systems in 3 open clusters
Short Name: J/AJ/155/51
IVOA Identifier: ivo://cds.vizier/j/aj/155/51
Access modes: tap#aux
Multi-capability service -- use get_service()

We identify and roughly characterize 66 candidate binary star systems in the
Pleiades, Praesepe, and NGC 2264 star clusters, based on robotic adaptive
optics imaging data obtained using Robo-AO at the Palomar 60" telescope. Only
~10% of our imaged pairs were previously known. We detect companions at red
optical wavelengths, with physical separations ranging from a few tens to a
few thousands of au. A three-sigma contrast curve generated for each final
image provides upper limits to the brightness ratios for any undetected
putative companions. The observations are sensitive to companions with a
maximum contrast of ~6^m^ at larger separations. At smaller separations, the
mean (best) raw contrast at 2" is 3.8^m^ (6^m^), at 1" is 3.0^m^ (4.5^m^), and
at 0.5" is 1.9^m^ (3^m^). Point-spread function subtraction can recover nearly
the full contrast in the closer separations. For detected candidate binary
pairs, we report separations, position angles, and relative magnitudes.
Theoretical isochrones appropriate to the Pleiades and Praesepe clusters are
then used to determine the corresponding binary mass ratios, which range from
0.2 to 0.9 in q=m_2_/m_1_. For our sample of roughly solar-mass (FGK type)
stars in NGC 2264 and sub-solar-mass (K and early M-type) primaries in the
Pleiades and Praesepe, the overall binary frequency is measured at
~15.5%+/-2%. However, this value should be considered a lower limit to the
true binary fraction within the specified separation and mass ratio ranges in
these clusters, given that complex and uncertain corrections for sensitivity
and completeness have not been applied.

Waveband Coverage: optical, infrared
---------------------------------------------  

Photometry & Li abund. of cool dwarfs in M35
Short Name: J/AJ/156/37
IVOA Identifier: ivo://cds.vizier/j/aj/156/37
Access modes: tap#aux
Multi-capability service -- use get_service()

Hydra spectra of 85 G-K dwarfs in the young cluster M35 near the Li 6708 {AA}
line region are analyzed. From velocities and Gaia astrometry, 78 are likely
single-star members that, combined with previous work, produce 108 members
with T_eff_ ranging from 6150 to 4000 K as defined by multicolor, broadband
photometry, E(B-V)=0.20, and [Fe/H]=-0.15, though there are indications the
metallicity may be closer to solar. The Lithium abundance A(Li) follows a
well-delineated decline from 3.15 for the hottest stars to upper limits =<1.0
among the coolest dwarfs. Contrary to earlier work, M35 includes single stars
at systematically higher A(Li) than the mean cluster relation. This subset
exhibits higher V_ROT_ than the more Li-depleted sample and, from photometric
rotation periods, is dominated by stars classed as convective (C); all others
are interface (I) stars. The cool, high-Li rapid rotators (RRs) are consistent
with models that simultaneously consider rapid rotation and radius inflation;
RRs hotter than the Sun exhibit excess Li depletion, as predicted by the
models. The A(Li) distribution with color and rotation period, when compared
to the Hyades/Praesepe and the Pleiades, is consistent with gyrochronological
analysis placing M35's age between the older M34 and younger Pleiades.
However, the Pleiades display a more excessive range in A(Li) and rotation
period than M35 on the low-Li, slow-rotation side of the distribution, with
supposedly younger stars at a given T_eff_ in the Pleiades spinning slower,
with A(Li) reduced by more than a factor of four compared to M35.

Waveband Coverage: infrared, optical
---------------------------------------------  

Candidates and members of the Pisces-Eridanus stream
Short Name: J/AJ/158/77
IVOA Identifier: ivo://cds.vizier/j/aj/158/77
Access modes: tap#aux
Multi-capability service -- use get_service()

Pisces-Eridanus (Psc-Eri), a nearby (d~80-226 pc) stellar stream stretching
across ~120{deg} of the sky, was recently discovered with Gaia data. The
stream was claimed to be ~1 Gyr old, which would make it an exceptional
discovery for stellar astrophysics, as star clusters of that age are rare and
tend to be distant, limiting their utility as benchmark samples. We test this
old age for Psc-Eri in two ways. First, we compare the rotation periods for
101 low-mass members (measured using time-series photometry from the
Transiting Exoplanet Survey Satellite) to those of well-studied open clusters.
Second, we identify 34 new high-mass candidate members, including the notable
stars {lambda} Tauri (an Algol-type eclipsing binary) and HD 1160 (host to a
directly imaged object near the hydrogen-burning limit). We conduct an
isochronal analysis of the color-magnitude data for these highest-mass
members, again comparing our results to those for open clusters. Both analyses
show that the stream has an age consistent with that of the Pleiades, i.e.,
~120 Myr. This makes the Psc-Eri stream an exciting source of young
benchmarkable stars and, potentially, exoplanets located in a more diffuse
environment that is distinct from that of the Pleiades and of other dense star
clusters.

Waveband Coverage: optical
---------------------------------------------  

Taurus members & nonmembers with K2 data
Short Name: J/AJ/159/273
IVOA Identifier: ivo://cds.vizier/j/aj/159/273
Access modes: tap#aux
Multi-capability service -- use get_service()

We present an analysis of K2 light curves (LCs) from Campaigns 4 and 13 for
members of the young (~3Myr) Taurus association, in addition to an older
(~30Myr) population of stars that is largely in the foreground of the Taurus
molecular clouds. Out of 156 of the highest-confidence Taurus members, we find
that 81% are periodic. Our sample of young foreground stars is biased and
incomplete, but nearly all stars (37/38) are periodic. The overall
distribution of rotation rates as a function of color (a proxy for mass) is
similar to that found in other clusters: the slowest rotators are among the
early M spectral types, with faster rotation toward both earlier FGK and later
M types. The relationship between period and color/mass exhibited by older
clusters such as the Pleiades is already in place by Taurus age. The
foreground population has very few stars but is consistent with the USco and
Pleiades period distributions. As found in other young clusters, stars with
disks rotate on average slower, and few with disks are found rotating faster
than ~2days. The overall amplitude of the LCs decreases with age, and higher-
mass stars have generally lower amplitudes than lower-mass stars. Stars with
disks have on average larger amplitudes than stars without disks, though the
physical mechanisms driving the variability and the resulting LC morphologies
are also different between these two classes.

Waveband Coverage: optical, infrared
---------------------------------------------  

X-ray studies of stars in the Pleiades
Short Name: J/ApJ/348/557
IVOA Identifier: ivo://cds.vizier/j/apj/348/557
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

Coronal X-ray emission of the Pleiades stars is investigated, and maximum
likelihood, integral X-ray luminosity functions are computed for Pleiades
members in selected color-index ranges. A detailed search is conducted for
long-term variability in the X-ray emission of those stars observed more than
once. An overall comparison of the survey results with those of previous
surveys confirms the ubiquity of X-ray emission in the Pleiades cluster stars
and its higher rate of emission with respect to older stars. It is found that
the X-ray emission from dA and early dF stars cannot be proven to be
dissimilar to that of Hyades and field stars of the same spectral type. The
Pleiades cluster members show a real rise of the X-ray luminosity from dA
stars to early dF stars. X-ray emission for the young, solar-like Pleiades
stars is about two orders of magnitude more intense than for the nearby solar-
like stars.

Waveband Coverage: x-ray
---------------------------------------------  

HST observations of low-mass stars in IC 348
Short Name: J/ApJ/541/977
IVOA Identifier: ivo://cds.vizier/j/apj/541/977
Access modes: tap#aux
Multi-capability service -- use get_service()

We investigate the low-mass population of the young cluster IC 348 down to the
deuterium-burning limit, a fiducial boundary between brown dwarf and planetary
mass objects, using a new and innovative method for the spectral
classification of late-type objects. Using photometric indices, constructed
from HST/NICMOS narrowband imaging, that measure the strength of the 1.9{mu}m
water band, we determine the spectral type and reddening for every M-type star
in the field, thereby separating cluster members from the interloper
population. Due to the efficiency of our spectral classification technique,
our study is complete from ~0.7 to 0.015M_{sun}_. The mass function derived
for the cluster in this interval, dN/dlogM{prop.to}M^0.5^, is similar to that
obtained for the Pleiades, but appears significantly more abundant in brown
dwarfs than the mass function for companions to nearby Sunlike stars. This
provides compelling observational evidence for different formation and
evolutionary histories for substellar objects formed in isolation versus as
companions. Because our determination of the IMF is complete to very low
masses, we can place interesting constraints on the role of physical processes
such as fragmentation in the star and planet formation process and the
fraction of dark matter in the Galactic halo that resides in substellar
objects.

Waveband Coverage: optical, infrared
---------------------------------------------  

Stellar rotation in M35
Short Name: J/ApJ/695/679
IVOA Identifier: ivo://cds.vizier/j/apj/695/679
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

We present the results of a five month photometric time-series survey for
stellar rotation over a 40'x40' field centered on the 150Myr open cluster M35
(=NGC 2168). We report rotation periods for 441 stars within this field and
determine their cluster membership and binarity based on a decade-long radial
velocity survey, proper-motion measurements, and multiband photometric
observations. We find that 310 of the stars with measured rotation periods are
late-type members of M35. The distribution of rotation periods for cluster
members span more than 2 orders of magnitude from ~0.1 to 15 days, not
constrained by the sampling frequency and the timespan of the survey. With an
age between the zero-age main sequence and the Hyades, and with ~6 times more
rotation periods than measured in the Pleiades, M35 permit detailed studies of
early rotational evolution of late-type stars. Nearly 80% of the 310 rotators
lie on two distinct sequences in the color-period plane, and define clear
relations between stellar rotation period and color (mass). The M35 color-
period diagram enables us to determine timescales for the transition between
the two rotational states, of ~60Myr and ~140Myr for G and K dwarfs,
respectively.

Waveband Coverage: optical, infrared
---------------------------------------------  

IN-SYNC. I. APOGEE stellar parameters
Short Name: J/ApJ/794/125
IVOA Identifier: ivo://cds.vizier/j/apj/794/125
Access modes: tap#aux
Multi-capability service -- use get_service()

Over two years, 8859 high-resolution H-band spectra of 3493 young (1-10Myr)
stars were gathered by the multi-object spectrograph of the APOGEE project as
part of the IN-SYNC ancillary program of the SDSS-III survey. Here we present
the forward modeling approach used to derive effective temperatures, surface
gravities, radial velocities, rotational velocities, and H-band veiling from
these near-infrared spectra. We discuss in detail the statistical and
systematic uncertainties in these stellar parameters. In addition, we present
accurate extinctions by measuring the E(J-H) of these young stars with respect
to the single-star photometric locus in the Pleiades. Finally, we identify an
intrinsic stellar radius spread of about 25% for late-type stars in IC 348
using three (nearly) independent measures of stellar radius, namely, the
extinction-corrected J-band magnitude, the surface gravity, and the Rsini from
the rotational velocities and literature rotation periods. We exclude that
this spread is caused by uncertainties in the stellar parameters by showing
that the three estimators of stellar radius are correlated, so that brighter
stars tend to have lower surface gravities and larger Rsini than fainter stars
at the same effective temperature.

Waveband Coverage: infrared, optical
---------------------------------------------  

Spitzer 3.6 and 4.5um monitoring of 5 stars
Short Name: J/ApJ/805/77
IVOA Identifier: ivo://cds.vizier/j/apj/805/77
Access modes: tap#aux
Multi-capability service -- use get_service()

Luminous debris disks of warm dust in the terrestrial planet zones around
solar-like stars were recently found to vary, which is indicative of ongoing
large-scale collisions of rocky objects. We use Spitzer 3.6 and 4.5um time-
series observations in 2012 and 2013 (extended to 2014 in one case) to monitor
five more debris disks with unusually high fractional luminosities ("extreme
debris disk"), including P1121 in the open cluster M47 (80 Myr), HD15407A in
the AB Dor moving group (80Myr), HD 23514 in the Pleiades (120Myr), HD145263
in the Upper Sco Association (10Myr), and the field star BD+20 307 (>~1Gyr).
Together with the published results for ID8 in NGC2547 (35Myr), this makes the
first systematic time-domain investigation of planetary impacts outside the
solar system. Significant variations with timescales shorter than a year are
detected in five out of the six extreme debris disks we monitored. However,
different systems show diverse sets of characteristics in the time domain,
including long-term decay or growth, disk temperature variations, and possible
periodicity.

Waveband Coverage: infrared
---------------------------------------------  

PTF stellar rotation periods for Pleiades members
Short Name: J/ApJ/822/81
IVOA Identifier: ivo://cds.vizier/j/apj/822/81
Access modes: tap#aux
Multi-capability service -- use get_service()

Stellar rotation periods (P_rot_) measured in open clusters have proved to be
extremely useful for studying stars' angular momentum content and rotationally
driven magnetic activity, which are both age- and mass-dependent processes.
While P_rot_ measurements have been obtained for hundreds of solar-mass
members of the Pleiades, measurements exist for only a few low-mass (<0.5
M_{sun}_) members of this key laboratory for stellar evolution theory. To fill
this gap, we report P_rot_ for 132 low-mass Pleiades members (including nearly
100 with M=<0.45 M_{sun}_), measured from photometric monitoring of the
cluster conducted by the Palomar Transient Factory in late 2011 and early
2012. These periods extend the portrait of stellar rotation at 125 Myr to the
lowest-mass stars and re-establish the Pleiades as a key benchmark for models
of the transport and evolution of stellar angular momentum. Combining our new
P_rot_ with precise BVIJHK photometry reported by Stauffer et al. (2007,
J/ApJS/172/663) and Kamai et al. (2014, J/AJ/148/30), we investigate known
anomalies in the photometric properties of K and M Pleiades members. We
confirm the correlation detected by Kamai et al. between a star's P_rot_ and
position relative to the main sequence in the cluster's color-magnitude
diagram. We find that rapid rotators have redder (V-K) colors than slower
rotators at the same V, indicating that rapid and slow rotators have different
binary frequencies and/or photospheric properties. We find no difference in
the photometric amplitudes of rapid and slow rotators, indicating that
asymmetries in the longitudinal distribution of starspots do not scale grossly
with rotation rate.

Waveband Coverage: optical, infrared
---------------------------------------------  

Praesepe members with K2 light curve data
Short Name: J/ApJ/839/92
IVOA Identifier: ivo://cds.vizier/j/apj/839/92
Access modes: tap#aux
Multi-capability service -- use get_service()

We have Fourier-analyzed 941 K2 light curves (LCs) of likely members of
Praesepe, measuring periods for 86% and increasing the number of rotation
periods (P) by nearly a factor of four. The distribution of P versus (V-Ks), a
mass proxy, has three different regimes: (V-Ks)<1.3, where the rotation rate
rapidly slows as mass decreases; 1.3<(V-Ks)<4.5, where the rotation rate slows
more gradually as mass decreases; and (V-Ks)>4.5, where the rotation rate
rapidly increases as mass decreases. In this last regime, there is a bimodal
distribution of periods, with few between ~2 and ~10 days. We interpret this
to mean that once M stars start to slow down, they do so rapidly. The K2
period-color distribution in Praesepe (~790Myr) is much different than that in
the Pleiades (~125Myr) for late F, G, K, and early-M stars; the overall
distribution moves to longer periods and is better described by two line
segments. For mid-M stars, the relationship has a similarly broad scatter and
is steeper in Praesepe. The diversity of LCs and of periodogram types is
similar in the two clusters; about a quarter of the periodic stars in both
clusters have multiple significant periods. Multi- periodic stars dominate
among the higher masses, starting at a bluer color in Praesepe ((V-Ks)~1.5)
than in the Pleiades ((V-Ks)~2.6). In Praesepe, there are relatively more LCs
that have two widely separated periods, {Delta}P>6days. Some of these could be
examples of M star binaries where one star has spun down but the other has
not.

Waveband Coverage: optical
---------------------------------------------  

PS1 proper-motion survey for brown dwarfs. I. Taurus
Short Name: J/ApJ/858/41
IVOA Identifier: ivo://cds.vizier/j/apj/858/41
Access modes: tap#aux
Multi-capability service -- use get_service()

We are conducting a proper-motion survey for young brown dwarfs in the Taurus-
Auriga molecular cloud based on the Pan-STARRS1 3{pi} Survey. Our search uses
multi-band photometry and astrometry to select candidates, and is wider
(370deg^2^) and deeper (down to ~3M_Jup_) than previous searches. We present
here our search methods and spectroscopic follow-up of our high-priority
candidates. Since extinction complicates spectral classification, we have
developed a new approach using low-resolution (R~100) near-infrared spectra to
quantify reddening-free spectral types, extinctions, and gravity
classifications for mid-M to late-L ultracool dwarfs (<=100-3M_Jup_ in
Taurus). We have discovered 25 low-gravity (VL-G) and the first 11
intermediate-gravity (INT-G) substellar (M6-L1) members of Taurus,
constituting the largest single increase of Taurus brown dwarfs to date. We
have also discovered 1 new Pleiades member and 13 new members of the Perseus
OB2 association, including a candidate very wide separation (58kau) binary. We
homogeneously reclassify the spectral types and extinctions of all previously
known Taurus brown dwarfs. Altogether our discoveries have thus far increased
the substellar census in Taurus by ~40% and added three more L-type members
(<~5-10M_Jup_). Most notably, our discoveries reveal an older (>10Myr) low-
mass population in Taurus, in accord with recent studies of the higher-mass
stellar members. The mass function appears to differ between the younger and
older Taurus populations, possibly due to incompleteness of the older stellar
members or different star formation processes.

Waveband Coverage: optical, infrared
---------------------------------------------  

Sp. obs. of rapidly rotating stars in the Pleiades
Short Name: J/ApJ/901/91
IVOA Identifier: ivo://cds.vizier/j/apj/901/91
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

Radial velocities for the early-type stars in the Pleiades cluster have always
been challenging to measure because of the significant rotational broadening
of the spectral lines. The large scatter in published velocities has led to
claims that many are spectroscopic binaries, and in several cases, preliminary
orbital solutions have been proposed. To investigate these claims, we obtained
and report here velocity measurements for 33 rapidly rotating B, A, and early
F stars in the Pleiades region, improving significantly on the precision of
the historical velocities for most objects. With one or two exceptions, we do
not confirm any of the previous claims of variability, and we also rule out
all four of the previously published orbital solutions, for HD 22637, HD
23302, HD 23338, and HD 23410. We do find HD 22637 to be a binary but with a
different period (71.8d). HD 23338 is likely a binary as well, with a
preliminary 8.7yr period also different from the one published. Additionally,
we report a 3635d orbit for HD 24899, another new spectroscopic binary in the
cluster. From the 32 bona fide members in our sample, we determine a mean
radial velocity for the Pleiades of 5.79+/-0.24km/s, or 5.52+/-0.31km/s when
objects with known visual companions are excluded. Adding these astrometric
binaries to the new spectroscopic ones, we find a lower limit to the binary
fraction among the B and A stars of 37%. In addition to the velocities, we
measure vsini for all stars, ranging between 69 and 317km/s.

Waveband Coverage: optical
---------------------------------------------  

The {mu}Tau Association (MUTA)
Short Name: J/ApJ/903/96
IVOA Identifier: ivo://cds.vizier/j/apj/903/96
Access modes: tap#aux
Multi-capability service -- use get_service()

We present an analysis of the newly identified {mu}Tau Association (MUTA) of
young stars at ~150pc from the Sun that is part of the large Cas-Tau
structure, coeval and comoving with the {alpha}Persei cluster. This
association is also located in the vicinity of the Taurus-Auriga star-forming
region and the Pleiades association, although it is unrelated to them. We
identify more than 500 candidate members of MUTA using Gaia DR2 data and the
BANYAN {Sigma} tool, and we determine an age of 62{+/-}7Myr for its population
based on an empirical comparison of its color-magnitude diagram sequence with
those of other nearby young associations. The MUTA association is related to
the Theia 160 group of Kounkel & Covey and corresponds to the e Tau group of
Liu et al. It is also part of the Cas-Tau group of Blaauw. As part of this
analysis, we introduce an iterative method based on spectral templates to
perform an accurate correction of interstellar extinction of Gaia DR2
photometry, needed because of its wide photometric bandpasses. We show that
the members of MUTA display an expected increased rate of stellar activity and
faster rotation rates compared with older stars, and that literature
measurements of the lithium equivalent width of nine G0- to K3-type members
are consistent with our age determination. We show that the present- day mass
function of MUTA is consistent with other known nearby young associations. We
identify WD0340+103 as a hot, massive white dwarf remnant of a B2 member that
left its planetary nebula phase only 270000yr ago, posing an independent age
constraint of 60_-6_^+8^ Myr for MUTA, consistent with our isochrone age. This
relatively large collection of comoving young stars near the Sun indicates
that more work is required to unveil the full kinematic structure of the
complex of young stars surrounding {alpha} Persei and Cas-Tau.

Waveband Coverage: optical, infrared
---------------------------------------------  

K2 LCs analysis of Sun-like stars in the Pleiades
Short Name: J/ApJ/916/66
IVOA Identifier: ivo://cds.vizier/j/apj/916/66
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

We analyze space-based time-series photometry of Sun-like stars, mostly in the
Pleiades, but also field stars and the Sun itself. We focus on timescales
between roughly 1hr and 1day. In the corresponding frequency band these stars
display brightness fluctuations with a decreasing power-law continuous
spectrum. K2 and Kepler observations show that the rms flicker due to this
mid-frequency continuum (MFC) can reach almost 1%, approaching the modulation
amplitude from active regions. The MFC amplitude varies by a factor up to 40
among Pleiades members with similar Teff, depending mainly on the stellar
Rossby number Ro. For Ro<=0.04, the mean amplitude is roughly constant at
about 0.4%; at larger Ro the amplitude decreases rapidly, shrinking by about
two orders of magnitude for Ro~1. Among stars, the MFC amplitude correlates
poorly with that of modulation from rotating active regions. Among field stars
observed for 3yr by Kepler, the quarterly average modulation amplitudes from
active regions are much more time variable than the quarterly MFC amplitudes.
We argue that the process causing the MFC is largely magnetic in nature and
that its power-law spectrum comes from magnetic processes distinct from the
star's global dynamo, with shorter timescales. By analogy with solar
phenomena, we hypothesize that the MFC arises from a (sometimes energetic)
variant of the solar magnetic network, perhaps combined with rotation-related
changes in the morphology of supergranules.

Waveband Coverage: optical, infrared
---------------------------------------------  

43yr spectrosc. monitoring of the Pleiades region
Short Name: J/ApJ/921/117
IVOA Identifier: ivo://cds.vizier/j/apj/921/117
Access modes: tap#aux
Multi-capability service -- use get_service()

We present the results of a spectroscopic monitoring program of the Pleiades
region aimed at completing the census of spectroscopic binaries in the
cluster, extending it to longer periods than previously reachable. We gathered
6104 spectra of 377 stars between 1981 and 2021, and merged our radial
velocities with 1151 measurements from an independent survey by others started
three years earlier. With the combined data spanning more than 43yr, we have
determined orbits for some 30 new binary and multiple systems, more than
doubling the number previously known in the Pleiades. The longest period is
36.5yr. A dozen additional objects display long-term trends in their
velocities, implying even longer periods. We examine the collection of orbital
elements for cluster members, and find that the shape of the incompleteness-
corrected distribution of periods (up to 104 days) is similar to that of
solar-type binaries in the field, while that of the eccentricities is
different. The mass-ratio distribution is consistent with being flat. The
binary frequency in the Pleiades for periods up to 104 days is 25%+/-3% after
corrections for undetected binaries, which is nearly double that of the field
up to the same period. The total binary frequency including known astrometric
binaries is at least 57%. We estimate the internal radial velocity dispersion
in the cluster to be 0.48+/-0.04km/s. We revisit the determination of the
tidal circularization period, and confirm its value to be 7.2+/-1.0d, with an
improved precision compared to an earlier estimate.

Waveband Coverage: optical
---------------------------------------------  

Pleiades members & escapee candidates with Gaia EDR3
Short Name: J/ApJ/926/132
IVOA Identifier: ivo://cds.vizier/j/apj/926/132
Access modes: tap#aux
Multi-capability service -- use get_service()

We search through an eight million cubic parsec volume surrounding the
Pleiades star cluster and the Sun to identify both the current and past
members of the Pleiades cluster within the Gaia EDR3 data set. We find nearly
1300 current cluster members and 289 former cluster candidates. Many of these
candidates lie well in front of or behind the cluster from our point of view,
so formerly they were considered cluster members, but their parallaxes put
them more than 10pc from the center of the cluster today. Over the past 100Myr
we estimate that the cluster has lost twenty percent of its mass including two
massive white dwarf stars and the {alpha}^2^ Canum Venaticorum type variable
star, 41 Tau. All three white dwarfs associated with the cluster are massive
(1.01-1.06M _{sun}_) and have progenitors with main-sequence masses of about
six solar masses. Although we did not associate any giant stars with the
cluster, the cooling time of the oldest white dwarf of 60Myr gives a firm
lower limit on the age of the cluster.

Waveband Coverage: optical
---------------------------------------------  

ROSAT Observations of the Pleiades
Short Name: J/ApJS/102/75
IVOA Identifier: ivo://cds.vizier/j/apjs/102/75
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

Of 214 stars in the core of the Pleiades, 99 were detected in X-rays with the
ROSAT PSPC. This catalog lists the characteristics of the stars taken from the
literature, in table1.dat and the rotational and X-ray characteristics in
table5.dat.

Waveband Coverage: x-ray, optical
---------------------------------------------  

Infrared observations of the Pleiades
Short Name: J/ApJS/172/663
IVOA Identifier: ivo://cds.vizier/j/apjs/172/663
Access modes: tap#aux
Multi-capability service -- use get_service()

We make use of new near- and mid-IR photometry of the Pleiades cluster in
order to help identify proposed cluster members. We also use the new
photometry with previously published photometry to define the single-star
main-sequence locus at the age of the Pleiades in a variety of color-magnitude
planes. The new near- and mid-IR photometry extend effectively 2 mag deeper
than the 2MASS All-Sky Point Source catalog, and hence allow us to select a
new set of candidate very low-mass and substellar mass members of the Pleiades
in the central square degree of the cluster. We identify 42 new candidate
members fainter than K_s_=14 (corresponding to 0.1M_{sun}_). These candidate
members should eventually allow a better estimate of the cluster mass function
to be made down to of order 0.04M_{sun}_. We also use new IRAC data, in
particular the images obtained at 8um, in order to comment briefly on
interstellar dust in and near the Pleiades.

Waveband Coverage: optical
---------------------------------------------  

KPNO spectroscopy of G & K dwarfs HIP stars
Short Name: J/ApJS/222/19
IVOA Identifier: ivo://cds.vizier/j/apjs/222/19
Access modes: tap#aux
Multi-capability service -- use get_service()

The tension between the Hipparcos parallax of the Pleiades and other
independent distance estimates continues even after the new reduction of the
Hipparcos astrometric data and the development of a new geometric distance
measurement for the cluster. A short Pleiades distance from the Hipparcos
parallax predicts a number of stars in the solar neighborhood that are sub-
luminous at a given photospheric abundance. We test this hypothesis using the
spectroscopic abundances for a subset of stars in the Hipparcos catalog, which
occupy the same region as the Pleiades in the color-magnitude diagram. We
derive stellar parameters for 170 nearby G- and K-type field dwarfs in the
Hipparcos catalog based on high-resolution spectra obtained using KPNO 4m
echelle spectrograph. Our analysis shows that, when the Hipparcos parallaxes
are adopted, most of our sample stars follow empirical color-magnitude
relations. A small fraction of stars are too faint compared to main-sequence
fitting relations by {Delta}M_V_>~0.3mag, but the differences are marginal at
a 2{sigma} level, partly due to relatively large parallax errors. On the other
hand, we find that the photometric distances of stars showing signatures of
youth as determined from lithium absorption line strengths and R'_HK_
chromospheric activity indices are consistent with the Hipparcos parallaxes.
Our result is contradictory to a suggestion that the Pleiades distance from
main-sequence fitting is significantly altered by stellar activity and/or the
young age of its stars, and provides an additional supporting evidence for the
long-distance scale of the Pleiades.

Waveband Coverage: optical
---------------------------------------------  

NGC 6649 UBV photometry
Short Name: J/MNRAS/224/61
IVOA Identifier: ivo://cds.vizier/j/mnras/224/61
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

A colour magnitude diagram to V=20 is given for 395 stars in the heavily
reddened open cluster NGC 6649. The absorption-corrected distance modulus is
11.00+/-0.15mag (1585+/-110pc) assuming R(OB)=3.27+/-0.10 for NGC 6649 and
based on a ZAMS with zero point referenced to a Pleiades distance modulus of
5.56mag. The range of reddening over the 5arcmin diameter of the cluster is
{DELTA}E(B-V)=0.3mag. NGC 6649 contains the double mode Cepheid V367 Sct,
which has <M_V_>=-3.80+/-0.06 and <B_0_>-<V_0_>=0.58+/-0.02.

Waveband Coverage: optical
---------------------------------------------  

Pleiades low-mass stars and brown dwarfs
Short Name: J/MNRAS/313/347
IVOA Identifier: ivo://cds.vizier/j/mnras/313/347
Access modes: tap#aux
Multi-capability service -- use get_service()

We present the results of a six-square-degree Pleiades survey in I and Z,
which is photometrically complete to approximately I_KP_=19.2mag (I_C_=19.6 in
the Pleiades). We remove non-cluster contamination on the basis of proper
motions and infrared photometry, and present 339 candidate cluster members, 30
of which are fainter than I_KP_=17.5, and are thus strong brown-dwarf
candidates.

Waveband Coverage: optical
---------------------------------------------  

BVI photometry of NGC 2547
Short Name: J/MNRAS/335/291
IVOA Identifier: ivo://cds.vizier/j/mnras/335/291
Access modes: tap#aux
Multi-capability service -- use get_service()

We have developed the techniques required to use Naylor's optimal photometry
algorithm of to create colour-magnitude diagrams with well-defined
completeness functions. To achieve this we first demonstrate that the optimal
extraction is insensitive to uncertainties in the measured position of the
star. We then show how to correct the optimally extracted fluxes such that
they correspond to those measured in a large aperture, so aperture photometry
of standard stars can be used to place the measurements on a standard system.
The technique simultaneously removes the effects of a position-dependent point
spread function. Finally, we develop a method called 'ghosting', which
calculates the completeness corrections in the absence of an accurate
description of the point spread function. We apply these techniques to the
young cluster NGC 2547 (=C0809-491), and use an X-ray-selected sample to find
an age of 20-35Myr and an intrinsic distance modulus of 8.00-8.15mag. We use
these isochrones to select members from our photometric surveys. Our derived
luminosity function shows a well-defined Wielen dip, making NGC 2547 the
youngest cluster in which such a feature has been observed. Our derived mass
function spans the range 0.1-6M_{sun}_ and is similar to that for the field
and the older, more massive clusters M35 and the Pleiades, supporting the idea
of a universal initial mass function.

Waveband Coverage: optical, infrared
---------------------------------------------  

Low-mass stars in M45 and M44
Short Name: J/MNRAS/342/1241
IVOA Identifier: ivo://cds.vizier/j/mnras/342/1241
Access modes: tap#aux
Multi-capability service -- use get_service()

We present near-infrared J-, H- and K-band photometry and optical spectroscopy
of low-mass star and brown dwarf (BD) candidates in the Pleiades and Praesepe
open clusters. We flag non-members from their position in K, I-K and J, J-K
colour-magnitude diagrams (CMDs), and J-H, H-K two-colour diagrams.

Waveband Coverage: infrared
---------------------------------------------  

HATNet Pleiades Rotation Period Catalogue
Short Name: J/MNRAS/408/475
IVOA Identifier: ivo://cds.vizier/j/mnras/408/475
Access modes: tap#aux
Multi-capability service -- use get_service()

Using data from the Hungarian-made Automated Telescope Network (HATNet) survey
for transiting exoplanets, we measure photometric rotation periods for 368
Pleiades stars with 0.4~<M~<1.3M_{sun}_. We detect periodic variability for 74
per cent of the cluster members in this mass range that are within our field-
of-view, and 93 per cent of the members with 0.7~<M~<1.0M_{sun}_. This
increases, by a factor of 5, the number of Pleiades members with measured
periods. We compare these data to the rich sample of spectroscopically
determined projected equatorial rotation velocities (vsini) available in the
literature for this cluster. Included in our sample are 14 newly identified
probable cluster members which have proper motions, photometry and rotation
periods consistent with membership.

Waveband Coverage: optical, infrared
---------------------------------------------  

UKIDSS Galactic Clusters Survey Pleiades members
Short Name: J/MNRAS/422/1495
IVOA Identifier: ivo://cds.vizier/j/mnras/422/1495
Access modes: tap#aux
Multi-capability service -- use get_service()

We present the results of a deep wide-field near-infrared survey of the entire
Pleiades cluster recently released as part of the UKIRT Infrared Deep Sky
Survey (UKIDSS) Galactic Clusters Survey (GCS) Data Release 9 (DR9). We have
identified a sample of ~1000 Pleiades cluster member candidates combining
photometry in five near-infrared passbands and proper motions derived from the
multiple epochs provided by the UKIDSS GCS DR9. We also provide revised
membership for all previously published Pleiades low-mass stars and brown
dwarfs in the past decade recovered in the UKIDSS GCS DR9 Pleiades survey
based on the new photometry and astrometry provided by the GCS.

Waveband Coverage: infrared
---------------------------------------------  

Pre-main-sequence isochrones. Pleiades benchmark
Short Name: J/MNRAS/424/3178
IVOA Identifier: ivo://cds.vizier/j/mnras/424/3178
Access modes: tap#aux
Multi-capability service -- use get_service()

We present a critical assessment of commonly used pre-main-sequence isochrones
by comparing their predictions to a set of well-calibrated colour-magnitude
diagrams of the Pleiades in the wavelength range 0.4-2.5um. Our analysis shows
that for temperatures less than 4000K, the models systematically overestimate
the flux by a factor of 2 at 0.5um, though this decreases with wavelength,
becoming negligible at 2.2um. In optical colours this will result in the ages
for stars younger than 10Myr being underestimated by factors of between 2 and
3. We show that using observations of standard stars to transform the data
into a standard system can introduce significant errors in the positioning of
pre-main sequences in colour-magnitude diagrams. Therefore, we have compared
the models to the data in the natural photometric system in which the
observations were taken. Thus we have constructed and tested a model of the
system responses for the Wide-Field Camera on the Isaac Newton Telescope. As a
benchmark test for the development of pre-main-sequence models, we provide
both our system responses and the Pleiades sequence.

Waveband Coverage: optical
---------------------------------------------  

M dwarfs in the Pleiades
Short Name: J/MNRAS/476/3245
IVOA Identifier: ivo://cds.vizier/j/mnras/476/3245
Access modes: tap#aux
Multi-capability service -- use get_service()

Rotation periods obtained with the Kepler satellite have been combined with
precise measurements of projected rotation velocity from the WIYN 3.5-m
telescope to determine the distribution of projected radii for several hundred
low-mass (0.1<=M/M_{sun}_<=0.8), fast-rotating members of the Pleiades
cluster. A maximum likelihood modelling technique, that takes account of
observational uncertainties, selection effects and censored data, and
considers the effects of differential rotation and unresolved binarity, has
been used to find that the average radius of these stars is 14+/-2 per cent
larger at a given luminosity than predicted by current evolutionary models of
Dotter et al. and Baraffe et al. The same models are a reasonable match to the
interferometric radii of older, magnetically inactive field M dwarfs,
suggesting that the over-radius may be associated with the young, magnetically
active nature of the Pleiades objects. No evidence is found for any change in
this over-radius above and below the boundary marking the transition to full
convection. Published evolutionary models that incorporate either the effects
of magnetic inhibition of convection or the blocking of flux by dark star-
spots do not individually explain the radius inflation, but a combination of
the two effects might. The distribution of projected radii is consistent with
the adopted hypothesis of a random spatial orientation of spin axes; strong
alignments of the spin vectors into cones with an opening semi-angle <30{deg}
can be ruled out. Any plausible but weaker alignment would increase the
inferred over-radius.

Waveband Coverage: optical, infrared
---------------------------------------------  

Radius inflation in Praesepe active M-dwarfs
Short Name: J/MNRAS/483/1125
IVOA Identifier: ivo://cds.vizier/j/mnras/483/1125
Access modes: tap#aux
Multi-capability service -- use get_service()

Rotation periods from Kepler K2 are combined with projected rotation
velocities from the WIYN 3.5m telescope to determine projected radii for fast-
rotating, low-mass (0.1<=M/M_{sun}_<=0.6) members of the Praesepe cluster. A
maximum likelihood analysis that accounts for observational uncertainties,
binarity, and censored data yields marginal evidence for radius inflation -
the average radius of these stars is 6+/-4 per cent larger at a given
luminosity than predicted by commonly used evolutionary models. This
overradius is smaller (at 2{sigma} confidence) than was found for similar
stars in the younger Pleiades using a similar analysis; any decline appears
due to changes occurring in higher mass (>0.25M_{sun}_) stars. Models
incorporating magnetic inhibition of convection predict an overradius, but do
not reproduce this mass dependence unless superequipartition surface magnetic
fields are present at lower masses. Models incorporating flux blocking by
starspots can explain the mass dependence but there is no evidence that spot
coverage diminishes between the Pleiades and Praesepe samples to accompany the
decline in overradius. The fastest rotating stars in both Praesepe and the
Pleiades are significantly smaller than the slowest rotators for which a
projected radius can be measured. This may be a selection effect caused by
more efficient angular momentum loss in larger stars leading to their
progressive exclusion from the analysed samples. Our analyses assume random
spin-axis orientations; any alignment in Praesepe, as suggested by Kovacs, is
strongly disfavoured by the broad distribution of projected radii.

Waveband Coverage: optical
---------------------------------------------  

NGTS clusters survey - I. Rotation in Blanco 1
Short Name: J/MNRAS/492/1008
IVOA Identifier: ivo://cds.vizier/j/mnras/492/1008
Access modes: tap#aux
Multi-capability service -- use get_service()

We determine rotation periods for 127 stars in the ~115-Myr-old Blanco 1 open
cluster using ~200d of photometric monitoring with the Next Generation Transit
Survey. These stars span F5-M3 spectral types (1.2M_{sun}_>~M>~0.3M_{sun}_)
and increase the number of known rotation periods in Blanco 1 by a factor of
four. We determine rotation periods using three methods: Gaussian process (GP)
regression, generalized autocorrelation function (G-ACF), and Lomb-Scargle
(LS) periodogram, and find that the GP and G-ACF methods are more applicable
to evolving spot modulation patterns. Between mid-F and mid-K spectral types,
single stars follow a well-defined rotation sequence from ~2 to 10d, whereas
stars in photometric multiple systems typically rotate faster. This may
suggest that the presence of a moderate-to-high mass ratio companion inhibits
angular momentum loss mechanisms during the early pre-main sequence, and this
signature has not been erased at ~100Myr. The majority of mid-F to mid-K stars
display evolving modulation patterns, whereas most M stars show stable
modulation signals. This morphological change coincides with the shift from a
well-defined rotation sequence (mid-F to mid-K stars) to a broad rotation
period distribution (late-K and M stars). Finally, we compare our rotation
results for Blanco 1 to the similarly aged Pleiades: the single-star
populations in both clusters possess consistent rotation period distributions,
which suggests that the angular momentum evolution of stars follows a well-
defined pathway that is, at least for mid-F to mid-K stars, strongly imprinted
by ~100Myr.

Waveband Coverage: optical
---------------------------------------------  

Gaia stars with GALEX NUV excess
Short Name: J/other/RMxAA/53
IVOA Identifier: ivo://cds.vizier/j/other/rmxaa/53.439
Access modes: tap#aux
Multi-capability service -- use get_service()

Accurate parallaxes from Gaia DR1 (TGAS) are combined with GALEX visual Nuv
magnitudes to produce absolute MNUV magnitudes and an ultraviolet HR diagram
for a large sample of astrometric stars. A functional fit is derived of the
lower envelope main sequence of the nearest 1403 stars (distance <40pc), which
should be reddening-free. Using this empirical fit, 50 nearby stars are
selected with significant Nuv excess. These are predominantly late K and early
M dwarfs, often associated with X-ray sources, and showing other
manifestations of magnetic activity. The sample may include systems with
hidden white dwarfs, stars younger than the Pleiades, or, most likely, tight
interacting binaries of the BY Dra-type. A separate collection of 40 stars
with precise trigonometric parallaxes and Nuv-G colors bluer than 2mag is
presented. It includes several known novae, white dwarfs, and binaries with
hot subdwarf (sdOB) components, but most remain unexplored.

Waveband Coverage: uv
---------------------------------------------  

On the evolution of angular momentum
Short Name: J/other/RMxAA/56
IVOA Identifier: ivo://cds.vizier/j/other/rmxaa/56.139
Access modes: tap#aux
Multi-capability service -- use get_service()

Selecting the best quality data, I find that nearly all 0.5 to 1.2M_{sun}_
main sequence stars converge to a single rotational mass dependent sequence
after 750Myr; when the mass is larger than 0.8M_{sun}_, most of them converge
in ~120Myr. If stars rotate as rigid bodies, the angular momentum of the vast
majority is within clearly outlined bounds. The lower boundary defines a
terminal main sequence rotational isochrone, the upper one coincides with slow
rotators from the Pleiades and stars from Praesepe delineate a third one. Mass
dependent exponential relationships between angular momentum and age are
determined from these isochrones. Age estimates based on the angular momentum,
are acceptable in middle aged stars older than 750Myr and more massive than
0.6-0.7M_{sun}_. The evolution of the Rossby number indicates that the Parker
dynamo may cease early on in stars where M/M_{sun}_>=1.1. An empirical formula
for the torque, an idealized model for it and a relation between rotational
period and magnetic field, lead to a formula for the evolution of the mass
loss rate, predicting that the present solar rate is close to a minimum and
that it was around five times more vigorous when life on Earth started.

Waveband Coverage:
---------------------------------------------  

Subaru NIR obs. of Pleiades stars in SEEDS survey
Short Name: J/PASJ/68/92
IVOA Identifier: ivo://cds.vizier/j/pasj/68/92
Access modes: tap#aux
Multi-capability service -- use get_service()

We find a new substellar companion to the Pleiades member star, Pleiades HII
3441, using the Subaru telescope with adaptive optics. The discovery is made
as part of the high-contrast imaging survey to search for planetary-mass and
substellar companions in the Pleiades and young moving groups. The companion
has a projected separation of 0.49+/-0.02 (66+/-2au) and a mass of 68+/-5MJ
based on three observations in the J-, H-, and Ks-bands. The spectral type is
estimated to be M7 (~2700K), and thus no methane absorption is detected in the
H band. Our Pleiades observations result in the detection of two substellar
companions including one previously reported among 20 observed Pleiades stars,
and indicate that the fraction of substellar companions in the Pleiades is
about 10.0^+26.1^_-8.8_%. This is consistent with multiplicity studies of both
the Pleiades stars and other open clusters.

Waveband Coverage: optical, infrared
---------------------------------------------  

Photometric rotation periods of stars in {alpha} Per
Short Name: V/140
IVOA Identifier: ivo://cds.vizier/v/140
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

We present the results from a photometric monitoring program of primarily
solar-type open cluster stars obtained during 1994 and 1995. Several members
of the {alpha} Persei cluster have been monitored and the corresponding
relation between coronal x-ray activity and rotation period derived. The
relation among mid-G/K type members illustrates both the previously noticed
downturn in L_X_/L_bol_ at high rotation rates and the sharp decrease in
coronal activity at long rotation periods as seen among Pleiades stars.
Intensive observation of one slowly rotating G-type member of IC 4665 has
enabled a period determination of 8-10 days to be made and illustrates the
need for (and limitations of) high quality observations.

Waveband Coverage: optical
---------------------------------------------  

NGC 2516 Cluster XMM-Newton X-Ray Point Source Catalog
Short Name: NGC2516XMM
IVOA Identifier: ivo://nasa.heasarc/ngc2516xmm
Access modes: tap#aux
Base URL: https://heasarc.gsfc.nasa.gov/xamin/vo/tap

This table contains the results from a deep X-ray survey of the young (~ 140
Myr), rich open cluster NGC 2516 obtained with the EPIC camera on board the
XMM-Newton satellite. By combining the data from six observations, a high
sensitivity, greater than a factor of 5 with respect to recent Chandra
observations, has been achieved. Kaplan-Meier estimators of the cumulative
X-ray luminosity distribution, statistically corrected for non-member
contaminants, were built by the authors and compared to those of the nearly
coeval Pleiades cluster. 431 X-ray sources were detected, and 234 of them have
as optical counterparts cluster stars spanning the entire NGC 2516 main
sequence. On the basis of X-ray emission and optical photometry, 20 new
candidate members of the cluster have been identified; at the same time there
are 49 X-ray sources without known optical or infrared counterpart. The X-ray
luminosities of cluster stars span the range log L<sub>x</sub> (erg
s<sup>-1</sup>) = 28.4 - 30.8. The representative coronal temperatures span
the 0.3 - 0.6 keV (3.5 - 8 MK) range for the cool component and 1.0 - 2.0 keV
(12 - 23 MK) for the hot one; similar values were found in other young open
clusters like the Pleiades, IC 2391, and Blanco 1. While no significant
differences were found in their X-ray spectra, NGC 2516 solar-type stars are
definitely less luminous in X-rays than their nearly coeval Pleiades
counterparts. The comparison with a previous ROSAT survey reveals the lack of
variability amplitudes larger than a factor of 2 in solar-type cluster stars
in a ~ 11 yr time scale, and thus activity cycles like in the Sun are probably
absent or have a different period and amplitude in young stars. NGC 2516 has
been observed several times with XMM-Newton during the first two years of
satellite operations for calibration purposes. The observations used in this
analysis span a period of 19 months with exposure times between 10 and 20 ks.
All of these observations have been performed with the thick filter. In the
combined EPIC datasets the authors detected 431 X-ray sources with a
significance level greater than 5.0 sigma, which should lead statistically to
at most one spurious source in the field of view.

Waveband Coverage: x-ray
---------------------------------------------  

NGC 2547 XMM-Newton X-Ray Point Source Catalog
Short Name: NGC2547XMM
IVOA Identifier: ivo://nasa.heasarc/ngc2547xmm
Access modes: tap#aux
Multi-capability service -- use get_service()

This table contains a list of point sources detected by XMM-Newton EPIC in a
pointing towards the young open cluster NGC 2547, made in order to allow the
authors to characterize coronal activity in solar-type stars, and stars of
lower mass, at an age of 30 Myr. X-ray emission was seen from stars at all
spectral types, peaking among G stars at luminosities (0.3 - 3 keV) of
L<sub>x</sub> ~= 10<sup>30.5</sup> erg/s and declining to L<sub>x</sub> <=
10<sup>29</sup> erg/s among M stars with masses >=0.2 solar masses. Coronal
spectra show evidence for multi-temperature differential emission measures and
low coronal metal abundances of Z~= 0.3. Most of the solar-type stars in NGC
2547 exhibit saturated or even supersaturated X-ray activity levels. The
median levels of L<sub>x</sub> and L<sub>x</sub>/L<sub>bol</sub> in the solar-
type stars of NGC 2547 are very similar to those in T-Tauri stars of the Orion
Nebula cluster (ONC), but an order of magnitude higher than in the older
Pleiades. The spread in X-ray activity levels among solar-type stars in NGC
2547 is much smaller than in older or younger clusters. This table contains
the properties of those X-ray sources which are correlated with optical
cluster members (see Section 2.2 of the reference paper for details on the
correlation procedure that was adopted), as well as the properties of those
X-ray sources which are uncorrelated with any optical cluster members. The
table lists the cross-identifications with optical catalogs for the candidate
cluster sources along with their X-ray luminosities and X-ray to bolometric
flux ratios, as well as the correlations between cluster members which were
detected by XMM-Newton and those detected 7 years earlier by the ROSAT HRI
instrument, along with the X-ray luminosities and flux ratios as determined by
the HRI.

Waveband Coverage: optical, x-ray
---------------------------------------------  

NGC 752 Chandra X-Ray Point Source Catalog
Short Name: NGC752CXO
IVOA Identifier: ivo://nasa.heasarc/ngc752cxo
Access modes: tap#aux
Multi-capability service -- use get_service()

This table provides a list of X-ray sources detected in a ~140 ks Chandra
X-ray observation of the open cluster NGC 752. For the sources with 2MASS
counterparts, the values of their magnitudes in the J, H and K bands are also
given. Very little is known about the evolution of stellar activity between
the ages of the Hyades (0.8 Gyr) and the Sun (4.6 Gyr). To gain information on
the typical level of coronal activity at a star&#39;s intermediate age, the
authors have studied the X-ray emission from stars in the 1.9 Gyr-old open
cluster NGC 752. They analyzed a ~ 140 ks Chandra observation of NGC 752 and a
~50 ks XMM-Newton observation of the same cluster. They detected 262 X-ray
sources in the Chandra data and 145 sources in the XMM-Newton observation.
Around 90% of the catalogued cluster members within Chandr&aacute;s field of
view are detected in the X-ray observation. The X-ray luminosity of all
observed cluster members (28 stars) and of 11 cluster member candidates was
derived. These data indicate that, at an age of 1.9 Gyr, the typical X-ray
luminosity L<sub>x</sub> of the cluster members with masses of 0.8 to 1.2
solar masses is 1.3 x 10<sup>28</sup> erg s<sup>-1</sup>, which is
approximately a factor of 6 times less intense than that observed in the
younger Hyades. Given that L<sub>x</sub> is proportional to the square of a
star&#39;s rotational rate, the median L<sub>x</sub> of NGC 752 is consistent,
for t >= 1 Gyr, with a decaying rate in rotational velocities v<sub>rot</sub>
~ t<sup>-alpha</sup> with alpha ~ 0.75, steeper than the Skumanich relation
(alpha ~ 0.5) and significantly steeper than that observed between the
Pleiades and the Hyades (where alpha <0.3), suggesting that a change in the
rotational regimes of the stellar interiors is taking place at an age of ~ 1
Gyr. The 135 ks observation of NGC 752 was performed by the Chandra ACIS
camera on September 29, 2003 starting at 21:11:59 UT. The X-ray source
detection was performed on the event list using the Wavelet Transform
detection algorithm developed at Palermo Astronomical Observatory PWDETECT,
available at http://oapa.astropa.unipa.it/progetti_ricerca/PWDetect
<http://oapa.astropa.unipa.it/progetti_ricerca/PWDetect>. Initially, the
energy range 0.2 - 10 keV was selected and the threshold for source detection
was taken as to ensure a maximum of 1-2 spurious sources per field. 169
sources were detected in this way. The analysis of these sources hardness
ratios showed, however, that all the catalogued stars in the field had low
hardness ratios, HR < ~ 0.2, where HR is the number of photons in the 2 - 8
keV band over the number in the 0.5 - 2 keV band. Thus, to maximize the
detection of stellar sources, PWDETECT was applied to the event list in the
energy range from 0.5 - 2 keV. Using a detection threshold which ensures less
than 1 spurious source per field leads to the detection of 188 sources, while
lowering this threshold to 10 spurious sources per field, allows 262 sources
to be identified in this energy range. This is a significant increase (well
above the number expected if all the additional sources were spurious), thus
the authors retained this list of 262 sources as their final list of sources
in the NGC 752 field, with the caveat that ~ 10 sources among them are likely
spurious. Note that the existence of ~ 10 spurious sources in the list is not
so much of a problem in this context, because cluster members or candidate
members are identified by the existence of a visible or near-IR counterpart.
The authors searched for 2MASS counterparts to the X-ray sources using the
2MASS Point Source Catalogue (PSC) and a search radius of 3 arcsec and found a
counterpart for 43 sources. Searching within the Point Source Reject Table of
the 2MASS Extended Mission leads to the further identification of 1
counterpart (source number 87).

Waveband Coverage: infrared, x-ray
---------------------------------------------  

NGC 752 XMM-Newton X-Ray Point Source Catalog
Short Name: NGC752XMM
IVOA Identifier: ivo://nasa.heasarc/ngc752xmm
Access modes: tap#aux
Multi-capability service -- use get_service()

This table provides a list of X-ray sources detected in a ~50 ks XMM-Newton
X-ray observation of the open cluster NGC 752. For the sources with 2MASS
counterparts, the values of their magnitudes in the J, H and K bands are also
given. Additionally, for the sources with a Chandra counterpart (within a
search radius of 5 arcsec), the values of their Chandra source number (as
given in the related Browse table NGC752CXO) are also given. Very little is
known about the evolution of stellar activity between the ages of the Hyades
(0.8 Gyr) and the Sun (4.6 Gyr). To gain information on the typical level of
coronal activity at a star&#39;s intermediate age, the authors have studied
the X-ray emission from stars in the 1.9 Gyr-old open cluster NGC 752. They
analyzed a ~ 140 ks Chandra observation of NGC 752 and a ~50 ks XMM-Newton
observation of the same cluster. They detected 262 X-ray sources in the
Chandra data and 145 sources in the XMM-Newton observation. Around 90% of the
catalogued cluster members within Chandr&aacute;s field of view are detected
in the X-ray observation. The X-ray luminosity of all observed cluster members
(28 stars) and of 11 cluster member candidates was derived. These data
indicate that, at an age of 1.9 Gyr, the typical X-ray luminosity
L<sub>x</sub> of the cluster members with masses of 0.8 to 1.2 solar masses is
1.3 x 10<sup>28</sup> erg s<sup>-1</sup>, which is approximately a factor of 6
times less intense than that observed in the younger Hyades. Given that
L<sub>x</sub> is proportional to the square of a star&#39;s rotational rate,
the median L<sub>x</sub> of NGC 752 is consistent, for t >= 1 Gyr, with a
decaying rate in rotational velocities v<sub>rot</sub> ~ t<sup>-alpha</sup>
with alpha ~ 0.75, steeper than the Skumanich relation (alpha ~ 0.5) and
significantly steeper than that observed between the Pleiades and the Hyades
(where alpha <0.3), suggesting that a change in the rotational regimes of the
stellar interiors is taking place at an age of ~ 1 Gyr. NGC 752 was observed
for 49 ks by the XMM-Newton EPIC camera on February 5, 2003 starting at
23:29:25 UT, and the nominal pointing was towards J2000.0 RA and Declination
of (01:57:38, +37:47:60), thus the XMM-Newton field-of-view (FOV) includes the
Chandra FOV. For the source detection, the authors used the PWXDETECT code
developed at Palermo Observatory and derived from the analogous Chandra
PWDETECT code based on wavelet transform analysis. This allows the three EPIC
exposures (PN, MOS1 and MOS2) to be combined in order to gain a deeper
sensitivity with respect to the source detection based on single images. There
were 145 point sources detected in the energy band 0.5 - 2.0 keV. An extended
source (not listed in this present table), very likely a galaxy cluster, is
also visible in the EPIC data. The authors searched for 2MASS counterparts to
the XMM-Newton sources using a search radius of 5 arcsec and found a
counterpart for 38 sources. As for the Chandra data, all sources with a
visible counterpart from DLM94 have also a 2MASS counterpart, so this leaves
15 XMM-Newton sources with a 2MASS counterpart and no counterpart in Daniel et
al. (1994, PASP, 106, 281); of these, 3 were also detected by Chandra; of the
other 12, 10 are outside the Chandra FOV, while two are within it (XMM-Newton
sources 58 and 65). Source 65 was caught by XMM-Newton during the decay phase
of a flare, which explains why it is not detected in the Chandra data. For
source 58 there is no immediate explanation for this, since the light curve
does not show evidence of a flare. No additional near-IR counterpart to the
XMM-Newton sources was found within the Point Source Reject Table of the 2MASS
Extended Mission.

Waveband Coverage: infrared, x-ray
---------------------------------------------  

ROSAT PSPC Catalog of the Pleiades (Micela et al. 1996)
Short Name: PSPC/Pleiades
IVOA Identifier: ivo://nasa.heasarc/pleiadxray
Access modes: tap#aux
Base URL: https://heasarc.gsfc.nasa.gov/xamin/vo/tap

This catalog contains the results of a deep X-ray survey of the core region of
the Pleiades open cluster carried out with ROSAT. In a single PSPC field (~1
degree in radius), 99 of 214 Pleiades stars are detected in X-rays, and upper
limits are computed for the remainder. This catalog lists the characteristics
of these stars taken from the literature, including their rotational data, as
well as their X-ray characteristics. The nucleus of the composite catalog used
in this study is the catalog compiled from the published literature for the
Einstein investigations of the Pleiades (Micela et al. 1990, ApJ, 348, 557).
This list has been extended by the results of recent surveys to a completeness
limit of visual magnitude of about 18.

Waveband Coverage: x-ray

Step 2: Acquire the relevant data and make a plot#

In order to query the table, we need the table name, note this is NOT the same as the short name we found above:

tables = tap_services[uniq_ind[1]].service.tables

short_name = "I/90"
# find table name:
for name in tables.keys():
    if short_name in name:
        print(name)

VI/90/archives
VI/90/maindata
VI/90/quality
VI/90/notes
VI/90/observer
I/90/catalog
VIII/90/first12

We can write code to eliminate the other cases (e.g., VI or VIII…) but we wanted to keep this cell to illustrate that the table name (which is required for the query) will likely include the short_name appended to “/catalog” (or “/table”).

But the other roman numeral catalogs are obviously different catalogs. Therefore try the below for a better match:

# find (more restricted) table name:
for name in tables.keys():
    if name.startswith(short_name):
        print(name)
        tablename=name

I/90/catalog

query = 'SELECT * FROM "%s"' %tablename
print(query)
results = tap_services[short_name].search(query)
results.to_table()

SELECT * FROM "I/90/catalog"

Table length=502

recno	Hertzsprung	CI	Ptm	RAB1900	e_RAs	DEB1900	e_DEs	rmsRA	rmsDE	rpmRA	rpmDE	DrpmRA	DrpmDE	DRA	DDE
		mag	mag	deg	ms	deg	mas			mas / yr	mas / yr	mas / yr	mas / yr	arcsec	arcsec
int32	int16	float64	float64	float64	float64	float64	int16	float64	float64	float64	float64	float64	float64	float64	float64
126	884	1.51	12.73	55.03883749999999	4.3	22.995927777777773	50	0.49	0.39	--	--	--	--	--	--
131	923	0.66	10.08	55.06343333333333	1.4	23.027888888888885	16	0.58	0.7	--	--	--	--	--	--
146	1021	1.26	10.42	55.12255833333332	1.5	23.011119444444443	18	0.41	0.64	--	--	--	--	--	--
90	712	1.05	13.21	54.91535416666666	5.8	23.042222222222218	65	0.5	0.42	--	--	--	--	--	--
107	802	0.0	14.44	54.97971666666666	5.2	23.035311111111106	61	0.4	0.33	--	--	--	--	--	--
124	882	1.15	12.55	55.038283333333325	3.4	23.09319722222222	43	0.42	0.48	--	--	--	--	--	--
111	815	0.82	12.01	54.986058333333325	2.7	23.118880555555553	33	0.61	0.49	--	--	--	--	--	--
66	580	0.3	12.65	54.82563333333333	9.7	22.981605555555554	96	0.25	0.22	--	--	--	--	--	--
51	490	0.9	13.03	54.74930416666666	6.0	23.054466666666663	68	0.41	0.51	--	--	--	--	--	--
...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...
127	885	1.14	11.94	55.03941249999999	4.8	24.55469722222222	62	0.31	0.34	--	--	--	--	--	--
103	775	0.75	12.84	54.959262499999994	5.2	24.565244444444442	65	0.38	0.56	--	--	--	--	--	--
122	880	0.8	13.35	55.037454166666656	6.4	24.571502777777773	76	0.38	0.62	--	--	--	--	--	--
7	285	0.58	11.29	54.562279166666656	8.6	24.42119166666666	89	0.62	0.11	--	--	--	--	--	--
18	324	1.18	12.78	54.60039583333332	7.3	24.45269444444444	92	0.58	0.34	--	--	--	--	--	--
16	320	0.9	10.89	54.59457916666666	3.7	24.457086111111106	43	0.71	0.93	--	--	--	--	--	--
9	293	0.74	10.71	54.567095833333326	7.5	24.463416666666664	82	1.07	0.99	--	--	--	--	--	--
13	314	0.69	10.51	54.59259999999999	3.0	24.480394444444443	38	0.65	0.71	--	--	--	--	--	--
34	405	0.53	9.8	54.67824999999999	2.4	24.503449999999997	30	0.53	0.84	-2.4	5.3	0.0	4.2	0.0	-0.1
41	453	0.82	13.26	54.719020833333325	9.7	24.57385833333333	116	0.31	0.67	--	--	--	--	--	--

We can access the column data as array using the .getcolumn(colname) attribute, where the colname is given in the table above. In particular the “CI” is the color index and “Ptm” is the photovisual magnitude. See here for details about the columns.

color = results.getcolumn('CI')
mag = results.getcolumn('Ptm')

Plotting#

Note: The magnitudes here are apparent and therefore in plotting, the color-magnitude diagram is typically brightness increasing upwards (higher y-axis) so we will flip the y-axis here.

plt.ylim(15, 0)
plt.ylabel("V [apparent mag]")
plt.xlabel("B-V")

plt.plot(color, mag, 'o', color='black')

[<matplotlib.lines.Line2D at 0x7ff7c28f94b0>]

../../_images/ef3c616dc1ad5708524385f3624ba15e414c9ebf75e7d4fa16b6fa2c61b37347.png

Step 3. Compare with other color-magnitude diagrams for Pleiades#

There is nice discussion here: http://www.southastrodel.com/Page03009a.htm about the color-magnitude diagram. Their Fig 4 looks slightly cleaner because part of this investigation was to select the 270 stars that are vetted members and restricted to stellar types more massive than K0.

The dataset is from Raboud+1998 (1998A&A…329..101R)

Therefore in this next step, we will use the bibcode to select this data and overplot with the previous data to compare.

bibcode = '1998A&A...329..101R' # Raboud
all_bibcodes = tap_services.getcolumn('source_value')
all_shortnames = tap_services.getcolumn('short_name')

match = np.where(all_bibcodes == bibcode)

# Show relevant short_name (for Raboud paper):
short_name = all_shortnames[match][0]
print(short_name)
print("----------")
ind = int(match[0])

tap_services[ind].describe()

J/A+A/329/101
----------
Masses of Pleiades members
Short Name: J/A+A/329/101
IVOA Identifier: ivo://cds.vizier/j/a+a/329/101
Access modes: tap#aux
Base URL: http://tapvizier.cds.unistra.fr/TAPVizieR/tap

On the basis of the best available member list and duplicity information, we
have studied the radial distribution of 270 stars and multiple systems earlier
than K0 in the Pleiades. Five new long period spectroscopic binaries have been
identified from the CORAVEL observations. We have found a clear mass
segregation between binaries and single stars, which is explained by the
greater average mass of the multiple systems. The mass function of the single
stars and primaries appears to be significantly different. While the central
part of the cluster is spherical, the outer part is clearly elliptical, with
an ellipticity of 0.17. The various parameters describing the Pleiades are
(for a distance of 125pc): core radius r_c_=0.6 deg (1.4pc), tidal radius
r_t_=7.4 (16pc), half mass radius r_m/2_=0.88 (1.9pc), harmonic radius r=1.82
(4pc). Low-mass stars (later than K0) probably extend further out and new
proper motion and radial velocity surveys over a larger area and to fainter
magnitudes would be very important to improve the description of the cluster
structure and complete mass function.

Waveband Coverage:

/tmp/ipykernel_2264/2733767379.py:11: DeprecationWarning: Conversion of an array with ndim > 0 to a scalar is deprecated, and will error in future. Ensure you extract a single element from your array before performing this operation. (Deprecated NumPy 1.25.)
  ind = int(match[0])

# Doing steps above to view table from Raboud+1998

# This 'tables' will return the same service tables as the 'tables' defined
# ealier in Step 2, since both the Eichhorn+1970 and Raboud+1998 come from the
# same service. Therfore, we did not need to redefine 'tables', but we kept it
# for completion, as different tables don't always use the same service.
tables = tap_services[ind].service.tables

# find table name:
for name in tables.keys():
    if short_name in name:
        tablename = name

# Another way to find the table name:
# Raboud_table = tap_services[short_name].get_tables()
# tablename = [name for name in Raboud_table.keys()][0]

query = 'SELECT * FROM "%s"' %tablename
print(query)
results = tap_services[ind].search(query)
results.to_table()

SELECT * FROM "J/A+A/329/101/table3"

Table length=270

recno	HII	Vmag	B-V	xpos	ypos	Dist	Mult	Rem	Mass	MassA	MassB	MassC	MassD
		mag	mag	arcmin	arcmin	arcmin			Msun	Msun	Msun	Msun	Msun
int32	int32	float64	float64	float64	float64	float64	int16	object	float64	float64	float64	float64	float64
1	25	9.47	0.48	-55.52	22.81	60.02	1		1.2	--	--	--	--
2	34	11.99	0.93	-53.62	33.49	63.22	1		0.81	--	--	--	--
3	97	12.62	1.08	-48.27	52.86	71.58	2	IRB	1.21	0.73	0.48	--	--
4	102	10.51	0.71	-49.4	-53.25	72.64	2	IRB	1.45	0.97	0.45	--	--
5	120	10.79	0.7	-47.4	-26.36	54.23	2	SB1	1.53	0.98	0.55	--	--
6	129	11.47	0.88	-46.91	-21.06	51.42	1		0.84	--	--	--	--
7	152	10.73	0.69	-46.07	-34.67	57.66	1		0.99	--	--	--	--
8	153	7.51	0.15	-44.39	57.94	72.99	1		1.74	--	--	--	--
9	157	7.9	0.34	-45.12	-27.97	53.08	2	SB	2.1	1.39	0.72	--	--
...	...	...	...	...	...	...	...	...	...	...	...	...	...
261	30419	9.35	0.58	-144.87	195.18	243.07	2	PHB	2.09	1.09	1.0	--	--
262	30679	12.2	1.0	-89.22	117.71	147.7	1		0.77	--	--	--	--
263	30700	11.14	0.71	-86.02	122.48	149.67	1		0.97	--	--	--	--
264	30909	8.58	0.29	-23.22	166.47	168.08	1		1.47	--	--	--	--
265	40131	11.33	0.81	45.0	181.82	187.31	1		0.89	--	--	--	--
266	40314	12.49	1.02	97.98	13.43	98.89	1		0.76	--	--	--	--
267	50088	10.72	0.81	84.43	-147.18	169.68	2	PHB	1.78	0.9	0.88	--	--
268	50151	9.17	0.44	112.1	-193.81	223.89	1		1.25	--	--	--	--
269	50198	10.86	0.71	129.27	-183.94	224.83	2	SB2	1.87	0.97	0.9	--	--
270	50308	11.46	0.82	159.43	-170.41	233.36	1		0.88	--	--	--	--

R98_color = results.getcolumn('B-V')
R98_mag = results.getcolumn('Vmag')

plt.ylim(15, 0)
plt.ylabel("V [apparent mag]")
plt.xlabel("B-V")
plt.plot(color, mag, 'o', markersize=4.0, color='black') ## This is Eichhorn data
plt.plot(R98_color, R98_mag, 's', markersize=5.0, color='red') ## This is new data from Raboud+98

[<matplotlib.lines.Line2D at 0x7ff7cc7aa380>]

../../_images/b7e29cce03cc9d6c7fcefd20620b3a59ea672629fb904c865480efecfdb4d18d.png

BONUS: Step 4: The CMD as a distance indicator#

Since the y-axis above is apparent magnitude, we can use the obvious features (e.g., main sequence curve) to translate the apparent magnitudes to absolute magnitudes (by comparing to published H-R diagrams given in absolute magnitudes) and measure the distance to Pleiades!

R98_color = results.getcolumn('B-V')
R98_mag = results.getcolumn('Vmag')

sun_color = 0.65  # from http://www.astro.ucla.edu/~wright/magcolor.htm
sun_mag = 10.4   # Played with this value until it looked centered in relation at the B-V color above (yellow star!)

plt.ylim(15, 0)
plt.ylabel("V [apparent mag]")
plt.xlabel("B-V")
plt.plot(color, mag, 'o', markersize=4.0, color='black') ## This is Eichhorn data
plt.plot(R98_color, R98_mag, 's', markersize=5.0, color='red') ## This is new data from Raboud+98
plt.plot(sun_color, sun_mag, '*', markersize=15.0, color='yellow') ## This is our estimated center point

[<matplotlib.lines.Line2D at 0x7ff7beb325f0>]

../../_images/247f91967efccb915462f5ac1d94170e075c4aae836f427efe8aafd0d10014a7.png

# Another measure... use the Sun:
Vabs = 4.8   ## Sun @ B-V = 0.65 (taken from Wikipedia)
Vapp = 10.4  ## Based on rough reading of plot above at B-V = 0.65

dm= Vapp - Vabs   # distance module = 5log d / 10pc.
dist = 10. ** (dm / 5. + 1.)
print("%10.1f pc " %dist)

     131.8 pc

True distance to Pleaides is 136.2 pc ( https://en.wikipedia.org/wiki/Pleiades ). Not bad!

HR (Hertzsprung-Russell) Diagram Solution

Contents