Properties of Radial Velocities measurement based on LAMOST-II
  Medium-Resolution Spectroscopic Observations
  The radial velocity (RV) is a basic physical quantity which can be determined
through Doppler shift of the spectrum of a star. The precision of RV
measurement depends on the resolution of the spectrum we used and the accuracy
of wavelength calibration. In this work, radial velocities of LAMOST-II medium
resolution (R ~ 7500) spectra are measured for 1,594,956 spectra (each spectrum
has two wavebands) through matching with templates. A set of RV standard stars
are used to recalibrate the zero point of the measurement, and some reference
sets with RVs derived from medium/high-resolution observations are used to
evaluate the accuracy of the measurement. Comparing with reference sets, the
accuracy of our measurement can get 0.0227 km s/1 with respect to radial
velocities standard stars. The intrinsic precision is estimated with the
multiple observations of single stars, which can achieve to 1.36 km s/1,1.08 km
s/1, 0.91 km s/1 for the spectra at signal-to-noise levels of 10, 20, 50,
respectively.
