- ID:
- ivo://CDS.VizieR/J/MNRAS/499/1890
- Title:
- Gaia white dwarfs within 40pc. II.
- Short Name:
- J/MNRAS/499/1890
- Date:
- 14 Jan 2022 00:10:10
- Publisher:
- CDS
- Description:
- We present an overview of the sample of northern hemisphere white dwarfs within 40pc of the Sun detected from Gaia Data Release 2 (DR2). We find that 521 sources are spectroscopically confirmed degenerate stars, 111 of which were first identified as white dwarf candidates from Gaia DR2 and followed-up recently with the William Herschel Telescope and Gran Telescopio Canarias. Three additional white dwarf candidates remain spectroscopically unobserved and six unresolved binaries are known to include a white dwarf but were not in our initial selection in the Gaia DR2 Hertzsprung-Russell diagram (HRD). Atmospheric parameters are calculated from Gaia and Pan-STARRS photometry for all objects in the sample, confirming most of the trends previously observed in the much smaller 20pc sample. Local white dwarfs are overwhelmingly consistent with Galactic disc kinematics, with only four halo candidates. We find that DAZ white dwarfs are significantly less massive than the overall DA population (MDAZ_avg_=0.59M_{sun}_, MDA_avg_=0.66M_{sun}_). It may suggest that planet formation is less efficient at higher mass stars, producing more massive white dwarfs. We detect a sequence of crystallised white dwarfs in the mass range from 0.6<=M/M_{sun}_<=1.0 and find that the vast majority of objects on the sequence have standard kinematic properties that correspond to the average of the sample, suggesting that their nature can be explained by crystallisation alone. We also detect 26 double degenerates and white dwarf components in 56 wide binary systems.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/839/89
- Title:
- 5 Galactic GC proper motions from Gaia DR1
- Short Name:
- J/ApJ/839/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a pilot study of Galactic globular cluster (GC) proper motion (PM) determinations using Gaia data. We search for GC stars in the Tycho-Gaia Astrometric Solution (TGAS) catalog from Gaia Data Release 1 (DR1), and identify five members of NGC 104 (47 Tucanae), one member of NGC 5272 (M3), five members of NGC 6121 (M4), seven members of NGC 6397, and two members of NGC 6656 (M22). By taking a weighted average of member stars, fully accounting for the correlations between parameters, we estimate the parallax (and, hence, distance) and PM of the GCs. This provides a homogeneous PM study of multiple GCs based on an astrometric catalog with small and well-controlled systematic errors and yields random PM errors similar to existing measurements. Detailed comparison to the available Hubble Space Telescope (HST) measurements generally shows excellent agreement, validating the astrometric quality of both TGAS and HST. By contrast, comparison to ground-based measurements shows that some of those must have systematic errors exceeding the random errors. Our parallax estimates have uncertainties an order of magnitude larger than previous studies, but nevertheless imply distances consistent with previous estimates. By combining our PM measurements with literature positions, distances, and radial velocities, we measure Galactocentric space motions for the clusters and find that these also agree well with previous analyses. Our analysis provides a framework for determining more accurate distances and PMs of Galactic GCs using future Gaia data releases. This will provide crucial constraints on the near end of the cosmic distance ladder and provide accurate GC orbital histories.
- ID:
- ivo://CDS.VizieR/J/ApJ/889/21
- Title:
- Galactic planetary nebulae with Gaia data
- Short Name:
- J/ApJ/889/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We matched the astrometry of central stars (CSs) of spectroscopically confirmed Galactic planetary nebulae (PNe) with DR2 Gaia parallaxes (p), finding 430 targets in common with p>0 and |{sigma}_p_/p|<1. A catalog of PNe whose CSs have DR2 Gaia parallaxes is presented in Table 1. We compared DR2 parallaxes with those in the literature, finding good correlation between the two samples. We used PNe parallaxes to calibrate the Galactic PN distance scale. Restricting the sample to objects with 20% parallax accuracy, we derive the distance scale log(R_pc_)=-(0.226+/-0.0155)xlog(S_H{beta}_)-(3.920+/-0.215), which represents a notable improvement with respect to previous ones. We found that the ionized mass versus optical thickness distance scale for Galactic PNe is not as constrained by the Gaia calibrators, but gives important insight into the nature of the PNe, and is essential to define the domain for our distance scale application. We placed the CSs whose distance has been determined directly by parallax on the HR diagram, and found that their location on the post-asymptotic-giant-branch (AGB) H-burning evolutionary tracks is typical for post-AGB stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/859/33
- Title:
- GOBELINS. IV. VLBA obs. of Taurus
- Short Name:
- J/ApJ/859/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new trigonometric parallaxes and proper motions of young stellar objects in the Taurus molecular cloud complex from observations collected with the Very Long Baseline Array as part of the Gould's Belt Distances Survey. We detected 26 young stellar objects and derived trigonometric parallaxes for 18 stars with an accuracy of 0.3% to a few percent. We modeled the orbits of six binaries and determined the dynamical masses of the individual components in four of these systems (V1023 Tau, T Tau S, V807 Tau, and V1000 Tau). Our results are consistent with the first trigonometric parallaxes delivered by the Gaia satellite and reveal the existence of significant depth effects. We find that the central portion of the dark cloud Lynds 1495 is located at d=129.5+/-0.3pc, while the B216 clump in the filamentary structure connected to it is at d=158.1+/-1.2pc. The closest and remotest stars in our sample are located at d=126.6+/-1.7pc and d=162.7+/-0.8pc, yielding a distance difference of about 36pc. We also provide a new distance estimate for HL Tau that was recently imaged. Finally, we compute the spatial velocity of the stars with published radial velocity and investigate the kinematic properties of the various clouds and gas structures in this region.
- ID:
- ivo://CDS.VizieR/J/ApJ/865/73
- Title:
- GOBELINS. V. Kinematics of Perseus
- Short Name:
- J/ApJ/865/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive the distance and structure of the Perseus molecular cloud by combining trigonometric parallaxes from Very Long Baseline Array (VLBA) observations, taken as part of the GOBELINS survey and Gaia Data Release 2. Based on our VLBA astrometry, we obtain a distance of 321+/-10pc for IC 348. This is fully consistent with the mean distance of 320+/-26 measured by Gaia. The VLBA observations toward NGC 1333 are insufficient to claim a successful distance measurement to this cluster. Gaia parallaxes, on the other hand, yield a mean distance of 293+/-22pc. Hence, the distance along the line of sight between the eastern and western edges of the cloud is ~30pc, which is significantly smaller than previously inferred. We use Gaia proper motions and published radial velocities to derive the spatial velocities of a selected sample of stars. The average velocity vectors with respect to the LSR are (u,v,w)=(-6.1+/-1.6, 6.8+/-1.1, -0.9+/-1.2) and (-6.4+/-1.0, 2.1+/-1.4, -2.4+/-1.0)km/s for IC 348 and NGC 1333, respectively. Finally, our analysis of the kinematics of the stars has shown that there is no clear evidence of expansion, contraction, or rotational motions within the clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/834/142
- Title:
- Gould's Belt Distances Survey (GOBELINS). II. OMC
- Short Name:
- J/ApJ/834/142
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the Gould's Belt Distances Survey of young star-forming regions toward the Orion Molecular Cloud Complex. We detected 36 young stellar objects (YSOs) with the Very Large Baseline Array, 27 of which have been observed in at least three epochs over the course of two years. At least half of these YSOs belong to multiple systems. We obtained parallax and proper motions toward these stars to study the structure and kinematics of the Complex. We measured a distance of 388+/-5pc toward the Orion Nebula Cluster, 428+/-10pc toward the southern portion L1641, 388+/-10pc toward NGC 2068, and roughly ~420pc toward NGC 2024. Finally, we observed a strong degree of plasma radio scattering toward {lambda} Ori.
- ID:
- ivo://CDS.VizieR/J/ApJS/201/19
- Title:
- Hawaii Infrared Parallax Program. I.
- Short Name:
- J/ApJS/201/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Astrometry and photometry for 318 ultracool dwarfs in 265 systems that have measured trigonometric parallaxes. To be included in this tabulation, an object must have a spectral type >=M6 or a K-band absolute magnitude >8.5mag. Parallaxes, proper motions, and coordinates at a specified epoch are given for all objects. Photometric measurements in MKO, 2MASS, Spitzer, and WISE systems are given when available. Various other flags that provide additional information about the object or photometry are included.
- ID:
- ivo://CDS.VizieR/J/ApJ/833/96
- Title:
- Hawaii infrared parallax program. II. Ultracool dwarfs
- Short Name:
- J/ApJ/833/96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a large, uniform analysis of young (~10-150Myr) ultracool dwarfs, based on new high-precision infrared (IR) parallaxes for 68 objects. We find that low-gravity (VL-G) late-M and L dwarfs form a continuous sequence in IR color-magnitude diagrams, separate from the field population and from current theoretical models. These VL-G objects also appear distinct from young substellar (brown dwarf and exoplanet) companions, suggesting that the two populations may have a different range of physical properties. In contrast, at the L/T transition, young, old, and spectrally peculiar objects all span a relatively narrow range in near-IR absolute magnitudes. At a given spectral type, the IR absolute magnitudes of young objects can be offset from ordinary field dwarfs, with the largest offsets occurring in the Y and J bands for late-M dwarfs (brighter than the field) and mid-/late-L dwarfs (fainter than the field). Overall, low-gravity (VL-G) objects have the most uniform photometric behavior, while intermediate gravity (INT-G) objects are more diverse, suggesting a third governing parameter beyond spectral type and gravity class. We examine the moving group membership for all young ultracool dwarfs with parallaxes, changing the status of 23 objects (including 8 previously identified planetary-mass candidates) and fortifying the status of another 28 objects. We use our resulting age-calibrated sample to establish empirical young isochrones and show a declining frequency of VL-G objects relative to INT-G objects with increasing age. Notable individual objects in our sample include high-velocity (>~100km/s) INT-G objects, very red late-L dwarfs with high surface gravities, candidate disk-bearing members of the MBM20 cloud and {beta} Pic moving group, and very young distant interlopers. Finally, we provide a comprehensive summary of the absolute magnitudes and spectral classifications of young ultracool dwarfs, using a combined sample of 102 objects found in the field and as substellar companions to young stars.
- ID:
- ivo://CDS.VizieR/J/AJ/159/257
- Title:
- Hawaii IR parallax program. IV. L0-T8 BDs with UKIRT
- Short Name:
- J/AJ/159/257
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present parallaxes, proper motions, and J-band photometry for 348 L and T dwarfs measured using the wide-field near-infrared camera (WFCAM) on the United Kingdom Infrared Telescope (UKIRT). This is the largest single batch of infrared parallaxes for brown dwarfs to date. Our parallaxes have a median uncertainty of 3.5mas, similar to most previous ground-based infrared parallax surveys. Our target list was designed to complete a volume-limited parallax sample of L0-T8 dwarfs out to 25pc spanning declinations -30{deg} to +60{deg} (68% of the sky). We report the first parallaxes for 165 objects, and we improve on previous measurements for another 53 objects. Our targets include 104 objects (mostly early-L dwarfs) having Gaia DR2 parallax measurements with which our parallaxes are consistent. We include an extensive comparison of previous literature parallaxes for L and T dwarfs with both our results and Gaia DR2 measurements, identifying systematic offsets for some previous surveys. Our parallaxes confirm that 14 objects previously identified as wide common proper motion companions to main-sequence stars have distances consistent with companionship. We also report new J_MKO_ photometry for our targets, including the first measurements for 193 of our targets and improvements over previously published J_MKO_ photometry for another 60 targets. Altogether, our parallaxes will enable the first population studies using a volume-limited sample spanning spectral types L0-T8 defined entirely by parallaxes.
- ID:
- ivo://CDS.VizieR/J/AJ/156/179
- Title:
- Highly r-process-enhanced field stars kinematics
- Short Name:
- J/AJ/156/179
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the kinematics of 35 highly r-process-enhanced ([Eu/Fe]>=+0.7) metal-poor (-3.8<[Fe/H]< -1.4) field stars. We calculate six-dimensional positions and velocities, evaluate energies and integrals of motion, and compute orbits for each of these stars using parallaxes and proper motions from the second Gaia data release (Cat. I/345) and published radial velocities. All of these stars have halo kinematics. Most stars (66%) remain in the inner regions of the halo (<13 kpc), and many (51%) have orbits that pass within 2.6 kpc of the Galactic center. Several stars (20%) have orbits that extend beyond 20 kpc, including one with an orbital apocenter larger than the Milky Way virial radius. We apply three clustering methods to search for structure in phase space, and we identify eight groups. No abundances are considered in the clustering process, but the [Fe/H] dispersions of the groups are smaller than would be expected by random chance. The orbital properties, clustering in phase space and metallicity, and the lack of highly r-process-enhanced stars on disk-like orbits, indicate that such stars likely were accreted from disrupted satellites. Comparison with the galaxy luminosity-metallicity relation suggests M_V_>~-9 for most of the progenitor satellites, characteristic of ultra-faint or low-luminosity classical dwarf spheroidal galaxies. Environments with low rates of star formation and Fe production, rather than the nature of the r-process site, may be key to obtaining the [Eu/Fe] ratios found in highly r-process-enhanced stars.
