Mapping the Galactic disk with the LAMOST and Gaia red clump sample: IV:
  the kinematic signature of the Galactic warp
  Using a sample of nearly 140,000 red clump stars selected from the LAMOST and
Gaia Galactic surveys, we have mapped mean vertical velocity $\overline{V_{z}}$
in the $X$-$Y$ plane for a large volume of the Galactic disk (6 $< R < 16$ kpc;
$-20 <\phi< 50^{\circ}$; $|Z| < 1$ kpc). A clear signature where
$\overline{V_{z}}$ increases with $R$ is detected for the chemically thin disk.
The signature for the thick disk is however not significant, in line with the
hot nature of this disk component. For the thin disk, the warp signature shows
significant variations in both radial and azimuthal directions, in excellent
agreement with the previous results of star counts. Fitting the two-dimensional
distribution of $\overline{V_{z}}$ with a simple long-lived static warp model
yields a line-of-node angle for this kinematic warp of about $12.5^{\circ}$,
again consistent with the previous results.
