摘要：Context.ForGaiaDR2, 280 million spectra collected by the Radial Velocity Spectrometer instrument on boardGaiawere processed, and median radial velocities were derived for 9.8 million sources brighter thanGRVS= 12 mag.Aims.This paper describes the validation and properties of the median radial velocities published inGaiaDR2.Methods.Quality tests and filters were applied to select those of the 9.8 million radial velocities that have the quality to be published inGaiaDR2. The accuracy of the selected sample was assessed with respect to ground-based catalogues. Its precision was estimated using both ground-based catalogues and the distribution of theGaiaradial velocity uncertainties.Results. GaiaDR2 contains median radial velocities for 7 224 631 stars, withTeffin the range [3550, 6900] K, which successfully passed the quality tests. The published median radial velocities provide a full-sky coverage and are complete with respect to the astrometric data to within 77.2% (forG≤ 12.5 mag). The median radial velocity residuals with respect to the ground-based surveys vary from one catalogue to another, but do not exceed a few 100 m s−1. In addition, theGaiaradial velocities show a positive trend as a function of magnitude, which starts aroundGRVS~ 9 mag and reaches about + 500 m s−1atGRVS= 11.75 mag. The origin of the trend is under investigation, with the aim to correct for it inGaiaDR3. The overall precision, estimated from the median of theGaiaradial velocity uncertainties, is 1.05 km s−1. The radial velocity precision is a function of many parameters, in particular, the magnitude and effective temperature. For bright stars,GRVS∈ [4, 8] mag, the precision, estimated using the full dataset, is in the range 220–350 m s−1, which is about three to five times more precise than the pre-launch specification of 1 km s−1. At the faint end,GRVS= 11.75 mag, the precisions forTeff= 5000 and 6500 K are 1.4 and 3.7 km s−1, respectively.
