- ID:
- ivo://CDS.VizieR/J/other/NewA/8.645
- Title:
- Vmag/plx relation for Hyades stars
- Short Name:
- J/other/NewA/8.6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, relation was established for Hyades stars between their apparent magnitudes and parallaxes. The precision criteria of this relation are very satisfactory. The importance of this relation was illustrated through its usages as: (1) A criterion for membership of the cluster, (2) a generating function for evaluating some parameters of the cluster.
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- ID:
- ivo://CDS.VizieR/J/AJ/161/42
- Title:
- Volume-limited sample of cool dwarfs. I. L0-T8 dwarfs
- Short Name:
- J/AJ/161/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new volume-limited sample of L0-T8 dwarfs out to 25pc defined entirely by parallaxes, using our recent measurements from UKIRT/WFCAM along with Gaia DR2 and literature parallaxes. With 369 members, our sample is the largest parallax-defined volume-limited sample of L and T dwarfs to date, yielding the most precise space densities for such objects. We find the local L0-T8 dwarf population includes 5.5%{+/-}1.2% young objects (<~200Myr) and 2.6%{+/-}1.6% subdwarfs, as expected from recent studies favoring representative ages <~4Gyr for the ultracool field population. This is also the first volume-limited sample to comprehensively map the transition from L to T dwarfs (spectral types ~L8-T4). After removing binaries, we identify a previously unrecognized, statistically significant (>4.4{sigma}) gap ~0.5mag wide in (J-K)_MKO_ colors in the L/T transition, i.e., a lack of such objects in our volume-limited sample, implying a rapid phase of atmospheric evolution. In contrast, the most successful models of the L/T transition to date-the "hybrid" models of Saumon & Marley-predict a pileup of objects at the same colors where we find a deficit, demonstrating the challenge of modeling the atmospheres of cooling brown dwarfs. Our sample illustrates the insights to come from even larger parallax-selected samples from the upcoming Legacy Survey of Space and Time by the Vera Rubin Obsevatory.
- ID:
- ivo://CDS.VizieR/J/AJ/161/102
- Title:
- VPDs and CMDs of Berkeley32, Berkeley98 and King23
- Short Name:
- J/AJ/161/102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the photometric and kinematical data from Gaia Data Release 2, three old open clusters namely Berkeley32 (Be32), Berkeley98 (Be98), and King23 are investigated. The latter two of these clusters are poorly studied in the literature. The numbers of the most probable cluster members are 563, 260, and 114 for Be32, Be98, and King23, respectively, with membership probabilities higher than 80% and lying within the clusters limiting radii. Mean proper motions (PMs; {mu}_{alpha}_cos_{delta}_ and {mu}_{delta}_) of the clusters are determined as (-0.34{+/-}0.008, -1.60{+/-}0.006), (-1.34{+/-}0.007, -3.22{+/-}0.008), and (-0.46{+/-}0.009, -0.87{+/-}0.012)mas/yr. The errors mentioned in the PMs are the Gaussian fitting errors. The blue straggler stars (BSS) in all three old clusters were found to exhibit centralized radial distribution. The clusters' radii are determined as 9.4', 12.95', and 6.6' for Be32, Be98, and King23 using radial density profiles. Ages of the clusters determined by isochrone fitting are 4.90{+/-}0.22, 3.23{+/-}0.15, and 1.95{+/-}0.22Gyr. The errors given in the clusters ages are the internal errors. The mass function slopes are found to be flatter than Salpeter's value for all three clusters. All three clusters are found to be dynamically relaxed. Galactic orbits are derived for these clusters, which demonstrate that the studied clusters follow a circular path around the Galactic center.
- ID:
- ivo://CDS.VizieR/J/MNRAS/472/675
- Title:
- Wide binaries in Tycho-Gaia: search method
- Short Name:
- J/MNRAS/472/675
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We mine the Tycho-Gaia astrometric solution (TGAS) catalogue for wide stellar binaries by matching positions, proper motions and astrometric parallaxes. We separate genuine binaries from unassociated stellar pairs through a Bayesian formulation that includes correlated uncertainties in the proper motions and parallaxes. Rather than relying on assumptions about the structure of the Galaxy, we calculate Bayesian priors and likelihoods based on the nature of Keplerian orbits and the TGAS catalogue itself. We calibrate our method using radial velocity measurements and obtain 7108 high-confidence candidate wide binaries with projected separations s<~1pc. The normalization of this distribution suggests that at least 0.7 per cent of TGAS stars have an associated, distant TGAS companion in a wide binary. We demonstrate that Gaia's astrometry is precise enough that it can detect projected orbital velocities in wide binaries with orbital periods as large as 10^6^yr. For pairs with s<~4x10^4^au, characterization of random alignments indicates our contamination to be 5-10 per cent. For s<~5x10^3^au, our distribution is consistent with Opik's law. At larger separations, the distribution is steeper and consistent with a power-law P(s){propto}s^-1.6^; there is no evidence in our data of any bimodality in this distribution for s<~1pc. Using radial velocities, we demonstrate that at large separations, i.e. of order s~1pc and beyond, any potential sample of genuine wide binaries in TGAS cannot be easily distinguished from ionized former wide binaries, moving groups or contamination from randomly aligned stars.
- ID:
- ivo://CDS.VizieR/I/238A
- Title:
- Yale Trigonometric Parallaxes, Fourth Edition
- Short Name:
- I/238A
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is a completely revised and enlarged edition of the General Catalogue of Trigonometric Stellar Parallaxes containing 15,994 parallaxes for 8,112 stars published before the end of 1995. In this Fourth Edition, 1,722 (27%) new stars have been added to those contained in the previous edition by Jenkins (1963). The mode of the parallax accuracy for the newly added stars (0.004" s.e.) is considerably better than in the previous editions (about 0.016"). Approximately 2300 stars are not in the Hipparcos Catalog. The catalog contains equatorial coordinates in the system of the FK4 for 1900, the total proper motion and its position angle, the weighted average absolute parallax and its standard error, the number of parallax observations, quality of interagreement of the different values, the visual magnitude and various cross identifications with other catalogs. Auxiliary information is listed, including UBV photometry, MK spectral types, data on the variability and binary nature of the stars, and miscellaneous information to aid in determining the reliability of the data.
- ID:
- ivo://CDS.VizieR/J/A+A/617/A135
- Title:
- 20 years of photometric microlensing
- Short Name:
- J/A+A/617/A135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Gaia DR2 offers unparalleled precision on stars' parallaxes and proper motions. This allows the prediction of microlensing events for which the lens stars (and any planets they possess) are nearby and may be well studied and characterised. We identify a number of potential microlensing events that will occur before the year 2035.5, 20 years from the Gaia DR2 reference epoch. We query Gaia DR2 for potential lenses within 100pc, extract parallaxes and proper motions of the lenses and background sources, and identify potential lensing events. We estimate the lens masses from Priam effective temperatures, and use these to calculate peak magnifications and the size of the Einstein radii relative to the lens stars' habitable zones. We identify 7 future events with a probability >10% of an alignment within one Einstein radius. Of particular interest is DR2 5918299904067162240 (WISE J175839.20-583931.6), magnitude G=14.9, which will lens a G=13.9 background star in early 2030, with a median 23% net magnification. Other pairs are typically fainter, hampering characterisation of the lens (if the lens is faint) or the ability to accurately measure the magnification (if the source is much fainter than the lens). Of timely interest is DR2 4116504399886241792 (2MASS J17392440-2327071), which will lens a background star in July 2020, albeit with weak net magnification (0.03%). Median magnifications for the other 5 high-probability events range from 0.3% to 5.3%. The Einstein radii for these lenses are 1-10 times the radius of the habitable zone, allowing these lensing events to pick out cold planets around the ice line, and filling a gap between transit and current microlensing detections of planets around very low-mass stars. We provide a catalogue of the predicted events to aid future characterisation efforts. Current limitations include a lack of many high-proper motion objects in Gaia DR2 and often large uncertainties on the proper motions of the background sources (or only 2-parameter solutions). Both of these deficiencies will be rectified with Gaia DR3 in 2020. Further characterisation of the lenses is also warranted to better constrain their masses and predict the photometric magnifications.
- ID:
- ivo://CDS.VizieR/J/ApJ/758/56
- Title:
- Young M dwarfs within 25pc. II. Kinematics
- Short Name:
- J/ApJ/758/56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a kinematic study of 165 young M dwarfs with ages of <~300Myr. Our sample is composed of stars and brown dwarfs with spectral types ranging from K7 to L0, detected by ROSAT and with photometric distances of <~25pc assuming that the stars are single and on the main sequence. In order to find stars kinematically linked to known young moving groups (YMGs), we measured radial velocities for the complete sample with Keck and CFHT optical spectroscopy and trigonometric parallaxes for 75 of the M dwarfs with the CAPSCam instrument on the du Pont 2.5m Telescope. Due to their youthful overluminosity and unresolved binarity, the original photometric distances for our sample underestimated the distances by 70% on average, excluding two extremely young (<~3Myr) objects found to have distances beyond a few hundred parsecs. We searched for kinematic matches to 14 reported YMGs and identified 10 new members of the AB Dor YMG and 2 of the Ursa Majoris group. Additional possible candidates include six Castor, four Ursa Majoris, two AB Dor members, and one member each of the Her-Lyr and {beta} Pic groups. Our sample also contains 27 young low-mass stars and 4 brown dwarfs with ages <~150Myr that are not associated with any known YMG. We identified an additional 15 stars that are kinematic matches to one of the YMGs, but the ages from spectroscopic diagnostics and/or the positions on the sky do not match. These warn against grouping stars together based only on kinematics and that a confluence of evidence is required to claim that a group of stars originated from the same star-forming event.
- ID:
- ivo://CDS.VizieR/J/AJ/159/200
- Title:
- Young stellar objects in Lupus star-forming region
- Short Name:
- J/AJ/159/200
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The identification and characterization of stellar members within a star-forming region are critical to many aspects of star formation, including formalization of the initial mass function, circumstellar disk evolution, and star formation history. Previous surveys of the Lupus star-forming region have identified members through infrared excess and accretion signatures. We use machine learning to identify new candidate members of Lupus based on surveys from two space-based observatories: ESA's Gaia and NASA's Spitzer. Astrometric measurements from Gaia's Data Release 2 and astrometric and photometric data from the Infrared Array Camera on the Spitzer Space Telescope, as well as from other surveys, are compiled into a catalog for the random forest (RF) classifier. The RF classifiers are tested to find the best features, membership list, non-membership identification scheme, imputation method, training set class weighting, and method of dealing with class imbalance within the data. We list 27 candidate members of the Lupus star-forming region for spectroscopic follow-up. Most of the candidates lie in Clouds V and VI, where only one confirmed member of Lupus was previously known. These clouds likely represent a slightly older population of star formation.
- ID:
- ivo://CDS.VizieR/J/ApJ/867/151
- Title:
- YSOs in the Gould Belt regions with Gaia-DR2 data
- Short Name:
- J/ApJ/867/151
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of the astrometric results from the Gaia second data release (DR2) for young stellar objects (YSOs) in star-forming regions related to the Gould Belt (GB). These regions are Barnard 59, Lupus 1 to 4, Chamaeleon I and II, {epsilon} Chamaeleontis, the Cepheus flare, IC 5146, and Corona Australis. The mean distance to the YSOs in each region is consistent with earlier estimations, though a significant improvement in the final errors was obtained. The mean distances to the star-forming regions were used to fit an ellipsoid of size (358+/-7)x(316+/-13)x(70+/-4)pc^3^, centered at (X0,Y0,Z0)=(-82+/-15,39+/-7,-25+/-4)pc, consistent with recently determined parameters of the GB. The mean proper motions were combined with radial velocities from the literature to obtain the three- dimensional motions of the star-forming regions, which are consistent with a general expansion of the GB. We estimate that this expansion is occurring at a velocity of 2.5+/-0.1km/s. This is the first time that motions of YSOs have been used to investigate the kinematics of the GB. As an interesting side result, we also identified stars with large peculiar velocities.
