- ID:
- ivo://CDS.VizieR/J/A+A/658/A22
- Title:
- Kinematic properties of white dwarfs
- Short Name:
- J/A+A/658/A22
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Kinematic and chemical tagging of stellar populations have both revealed much information on the past and recent history of the Milky Way, including its formation history, merger events, and mixing of populations across the Galactic disk and halo. We present the first detailed 3D kinematic analysis of a sample of 3133 white dwarfs that used Gaia astrometry plus radial velocities, which were measured either by Gaia or by ground-based spectroscopic observations. The sample includes either isolated white dwarfs that have direct radial velocity measurements, or white dwarfs that belong to common proper motion pairs that contain nondegenerate companions with available radial velocities. A subset of common proper motion pairs also have metal abundances that have been measured by large-scale spectroscopic surveys or by our own follow-up observations. We used the white dwarfs as astrophysical clocks by determining their masses and total ages through interpolation with dedicated evolutionary models. We also used the nondegenerate companions in common proper motions to chemically tag the population. Combining accurate radial velocities with Gaia astrometry and proper motions, we derived the velocity components of our sample in the Galactic rest frame and their Galactic orbital parameters. The sample is mostly located within ~300 pc from the Sun. It predominantly contains (90-95%) thin-disk stars with almost circular Galactic orbits, while the remaining 5-10% of stars have more eccentric trajectories and belong to the thick disk. We identified seven isolated white dwarfs and two common proper motion pairs as halo members. We determined the age - velocity dispersion relation for the thin-disk members, which agrees with previous results that were achieved from different white dwarf samples without published radial velocities. The age - velocity dispersion relation shows signatures of dynamical heating and saturation after 4-6 Gyr. We observed a mild anticorrelation between [Fe/H] and the radial component of the average velocity dispersion, showing that dynamical mixing of populations takes place in the Galactic disk, as was detected through the analysis of other samples of FGK stars. We have shown that a white dwarf sample with accurate 3D kinematics and well-measured chemical compositions enables a wider understanding of their population in the solar neighborhood and its connection with the Galactic chemodynamics. The legacy of existing spectroscopic surveys will be boosted by the availability of upcoming larger samples of white dwarfs and common proper motion pairs with more uniform high-quality data.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/125/1397
- Title:
- Kinematics, age and abundances of open clusters
- Short Name:
- J/AJ/125/1397
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have compiled two new open cluster catalogs. In the first one, there are 119 objects with ages, distances, and metallicities available, while in the second one, 144 objects have both absolute proper motion and radial velocity data, of which 45 clusters also have metallicity data available.
- ID:
- ivo://CDS.VizieR/J/ApJS/61/667
- Title:
- Kinematics of Galactic old population
- Short Name:
- J/ApJS/61/667
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A catalog is presented of some 1200 Galactic objects which have radial velocities and abundances [Fe/H]<=-0.6. These data have been analyzed to yield information on the kinematic properties of the older populations of the Galaxy and on the interdependence between kinematics and abundance.
- ID:
- ivo://CDS.VizieR/J/MNRAS/421/3362
- Title:
- Kinematics of galactic red clump stars
- Short Name:
- J/MNRAS/421/3362
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate radial and vertical metallicity gradients for a sample of red clump stars from the RAdial Velocity Experiment (RAVE) Data Release 3. We select a total of 6781 stars, using a selection of colour, surface gravity and uncertainty in the derived space motion, and calculate for each star a probabilistic (kinematic) population assignment to a thin or thick disc using space motion and additionally another (dynamical) assignment using stellar vertical orbital eccentricity.
- ID:
- ivo://CDS.VizieR/J/ApJ/769/87
- Title:
- Kinematics of halo red giants
- Short Name:
- J/ApJ/769/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explore the kinematics and orbital properties of a sample of red giants in the halo system of the Milky Way that are thought to have formed in globular clusters based on their anomalously strong UV/blue CN bands. The orbital parameters of the CN-strong halo stars are compared to those of the inner- and outer-halo populations as described by Carollo et al. (2007Natur.450.1020C, 2010ApJ...712..692C), and to the orbital parameters of globular clusters with well-studied Galactic orbits. The CN-strong field stars and the globular clusters both exhibit kinematics and orbital properties similar to the inner-halo population, indicating that stripped or destroyed globular clusters could be a significant source of inner-halo field stars, and suggesting that both the CN-strong stars and the majority of globular clusters are primarily associated with this population.
- ID:
- ivo://CDS.VizieR/J/ApJS/96/175
- Title:
- Kinematics of Metal-Poor Stars. I.
- Short Name:
- J/ApJS/96/175
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We discuss the kinematic properties of a sample of 1936 Galactic stars, selected without kinematic bias, and with abundances [Fe/H] <= -0.6. The stars selected for this study all have measured radial velocities, and the majority have abundances determined from spectroscopic and narrow-/intermediate-band photometric techniques. In contrast to previous examinations of the kinematics of the metal-poor stars in the Galaxy, our sample contains large numbers of stars that are located at distances in excess of 1 kpc from the Galactic plane. Thus, a much clearer picture of the nature of the metal-deficient populations in the Galaxy can now be drawn. Our present data can be well described in terms of a two-component kinematic model consisting of a thick disk, rotating at roughly 200 km/s (independent of metal abundance), and an essentially nonrotating halo. The kinematics of these two components suggest a very broad overlap in metallicity; the thick disk is shown to possess an extremely metal-weak tail, extending to abundances even lower than previously reported, down to at least [Fe/H] ~ -2.0. A "minimal-assumptions" maximum-likelihood model is used to show that below [Fe/H] = -1.5 roughly 30% of stars in the solar neighbourhood can be kinematically associated with the thick disk. Over the metallicity interval -1.6 <= [Fe/H] <= -1.0, the thick-disk proportion rises to 60%. This fraction is only slightly smaller than contribution of thick-disk stars derived by Morrison, Flynn, and Freeman in the same metallicity interval (80%). Our confirmation that significant numbers of stars with thick-disk-like kinematics exist in the solar neighbourhood at arbitrarily low metal abundance suggests that previous disagreements about the correlation of population rotation velocities and metal abundance (e.g. Sandage & Fouts vs. Norris) may be due primarily to the selection criteria employed, and the resulting different contribution of metal-weak thick-disk stars to the respective data sets. The non-Gaussian nature of the velocity distribution of extremely metal-poor stars ([Fe/H] <= -1.5) in the directions of the Galactic poles reported by previous workers can also be understood as a consequence of the overlap between a cold metal-weak thick-disk population and a hot halo population. A maximum-likelihood technique has been developed in order to estimate the velocity ellipsoids of the thick-disk and halo components of the Galaxy. From the 349 stars in our sample with -1.0 <= [Fe/H] <= -0.6 and |z| <= 1 kpc, the velocity ellipsoid of the thick disk is (sigma_U, sigma_V, sigma_W) = (63 +/- 7, 42 +/- 4, 38 +/- 4) km/s. These values are in remarkably good accord with the predicted thick-disk velocity ellipsoid obtained by Quinn, Hernquist, and Fullagar from simulations of a satellite-merger formation scenario. Based on this velocity ellipsoid, a radial scale length for thick-disk stars of h_R = 4.7 +/- 0.5 kpc is obtained, larger than reported by Morrison, and similar to the value obtained for the old-disk population. However, the apparent equality of sigma_V and sigma_W is evidence that the thick disk is kinematically distinct from the old-disk population, where sigma_V:sigma_W ~ 2^{1/2}:1. We find a substantially smaller asymmetric-drift velocity gradient for presumed thick-disk stars (delta Vrot/delta |z| = -13 +/- 6 km/s/kpc) than reported by Majewski (delta Vrot/delta |z| = -21 +/- 1 km/s/kpc). From 887 stars in our sample with [Fe/H] <= -1.5 the local velocity ellipsoid of the halo is (sigma_r, sigma_phi, sigma_theta) = (153 +/- 10, 93 +/- 18, 107 +/- 7) km/s, that is, strongly radially peaked, as indicated by previous studies. We find little difference in the velocity ellipsoids of this sample when it is split into two roughly equal pieces with -2.2 <= [Fe/H] <= -1.5 and [Fe/H] <= -2.2, which indicates a lack of radial metallicity gradient in the halo, as found from studies of the Galactic globular cluster system. The velocity ellipsoid obtained from the small number of stars in our sample with Galactocentric distances r > 10 kpc (N = 61) is (sigma_r, sigma_phi, sigma_theta) = (115 +/- 18, 138 +/- 78, 110 +/- 24) km/s, much less radially elongated than found for the local sample.
- ID:
- ivo://CDS.VizieR/J/ApJ/836/202
- Title:
- Kinematic study of the Leo II dwarf galaxy
- Short Name:
- J/ApJ/836/202
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We conducted a large spectroscopic survey of 336 red giants in the direction of the Leo II dwarf galaxy using Hectochelle on the Multiple Mirror Telescope, and we conclude that 175 of them are members based on their radial velocities and surface gravities. Of this set, 40 stars have never before been observed spectroscopically. The systemic velocity of the dwarf is 78.3+/-0.6km/s with a velocity dispersion of 7.4+/-0.4km/s. We identify one star beyond the tidal radius of Leo II but find no signatures of uniform rotation, kinematic asymmetries, or streams. The stars show a strong metallicity gradient of -1.53+/-0.10dex/kpc and have a mean metallicity of -1.70+/-0.02dex.
- ID:
- ivo://CDS.VizieR/J/ApJ/836/167
- Title:
- K2 planetary syst. around low-mass stars. I.
- Short Name:
- J/ApJ/836/167
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present near-infrared spectra for 144 candidate planetary systems identified during Campaigns 1-7 of the NASA K2 Mission. The goal of the survey was to characterize planets orbiting low-mass stars, but our Infrared Telescope Facility/SpeX and Palomar/TripleSpec spectroscopic observations revealed that 49% of our targets were actually giant stars or hotter dwarfs reddened by interstellar extinction. For the 72 stars with spectra consistent with classification as cool dwarfs (spectral types K3-M4), we refined their stellar properties by applying empirical relations based on stars with interferometric radius measurements. Although our revised temperatures are generally consistent with those reported in the Ecliptic Plane Input Catalog (EPIC), our revised stellar radii are typically 0.13R_{sun}_ (39%) larger than the EPIC values, which were based on model isochrones that have been shown to underestimate the radii of cool dwarfs. Our improved stellar characterizations will enable more efficient prioritization of K2 targets for follow-up studies.
- ID:
- ivo://CDS.VizieR/J/ApJS/222/19
- Title:
- KPNO spectroscopy of G & K dwarfs HIP stars
- Short Name:
- J/ApJS/222/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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.
- ID:
- ivo://CDS.VizieR/J/ApJS/247/28
- Title:
- K2 star parameters from Gaia & LAMOST
- Short Name:
- J/ApJS/247/28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Previous measurements of stellar properties for K2 stars in the Ecliptic Plane Input Catalog (EPIC) largely relied on photometry and proper motion measurements, with some added information from available spectra and parallaxes. Combining Gaia DR2 distances with spectroscopic measurements of effective temperatures, surface gravities, and metallicities from the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) DR5, we computed updated stellar radii and masses for 26838 K2 stars. For 195250 targets without a LAMOST spectrum, we derived stellar parameters using random forest regression on photometric colors trained on the LAMOST sample. In total, we measured spectral types, effective temperatures, surface gravities, metallicities, radii, and masses for 222088 A, F, G, K, and M-type K2 stars. With these new stellar radii, we performed a simple reanalysis of 299 confirmed and 517 candidate K2 planet radii from Campaigns 1-13, elucidating a distinct planet radius valley around 1.9R_{Earth}_, a feature thus far only conclusively identified with Kepler planets, and tentatively identified with K2 planets. These updated stellar parameters are a crucial step in the process toward computing K2 planet occurrence rates.
