Radial Velocity Comparison of Gaia DR2 and RAVE DR5 Survey: A Systematic Offset in Radial Velocities among a Group of Highly Accurate Radial Velocity Stars

Abstract

Here, we report a comparative study of radial velocity (RV) data of two major surveys: Gaia Data Release 2 and RAVE Data Release 5. We restricted the sample to stars with relatively accurate RVs ({σ }_RV}_{Gaia}}≤slant 2 km s^-1 or ≤2%, and {σ }_RV}_RAVE}}≤slant 2 km s^-1 or ≤2%). The difference between RV _Gaia and RV_RAVE for a majority of the sample follows a normal distribution with mean = 0.28 km s^-1 and σ = 1.49 km s^-1. However, we found a very small group of stars (≈0.08% of the total) for which the difference in RVs between the two surveys is significantly larger with an offset of -104.50 km s^-1 with σ = 4.92 km s^-1. Kinematics based on RV _Gaia suggest that most of the group members belong to the Galactic thin disk, which agrees with the group’s metallicity range of -1.2 to +0.5 dex suggesting the offset in RV is probably due to RAVE velocity data for this particular group.