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