Kinematic properties of white dwarfs. Galactic orbital parameters and age-velocity dispersion relation

TL;DR

This study provides a comprehensive 3D kinematic analysis of 3133 white dwarfs using Gaia data and radial velocities, revealing their Galactic orbital properties, ages, and the age-velocity dispersion relation in the Milky Way's disk.

Contribution

First detailed 3D kinematic analysis of a large white dwarf sample combining Gaia astrometry, radial velocities, and chemical tagging to study Galactic dynamics and stellar populations.

Findings

Majority are thin-disk stars with circular orbits.

Identified halo white dwarfs and their properties.

Age-velocity dispersion relation shows dynamical heating saturation after 4-6 Gyr.

Abstract

We present the first detailed 3D kinematic analysis of a sample of 3133 white dwarfs that use 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 via interpolation with dedicated evolutionary models. We also used the nondegenerate companions in common proper motions to chemically tag of 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 contains predominantly (90-95%) thin-disk stars with close-to-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 shows signatures of dynamical heating and saturation after 4-6 Gyr. We observed a mild anti-correlation 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 via the analysis of other samples of FGK stars. [Abridged]