The GALAH Survey: Accurate Radial Velocities and Library of Observed
  Stellar Template Spectra
  GALAH is a large-scale magnitude-limited southern stellar spectroscopic
survey. Its second data release (GALAH DR2) provides values of stellar
parameters and abundances of 23 elements for 342,682 stars (Buder et al.). Here
we add a description of the public release of radial velocities with a typical
accuracy of 0.1 km/s for 336,215 of these stars, achievable due to the large
wavelength coverage, high resolving power and good signal to noise ratio of the
observed spectra, but also because convective motions in stellar atmosphere and
gravitational redshift from the star to the observer are taken into account. In
the process we derive medians of observed spectra which are nearly noiseless,
as they are obtained from between 100 and 1116 observed spectra belonging to
the same bin with a width of 50 K in temperature, 0.2 dex in gravity, and 0.1
dex in metallicity. Publicly released 1181 median spectra have a resolving
power of 28,000 and trace the well-populated stellar types with metallicities
between -0.6 and +0.3. Note that radial velocities from GALAH are an excellent
match to the accuracy of velocity components along the sky plane derived by
Gaia for the same stars. The level of accuracy achieved here is adequate for
studies of dynamics within stellar clusters, associations and streams in the
Galaxy. So it may be relevant for studies of the distribution of dark matter.
