Kinematic versus Spectroscopic Radial Velocities for the Gaia RVS
Résumé
The Gaia spectrometer (RVS) has no built-in calibration device and the RVS will rely on its own observations to carry out the wavelength calibration. A small sample (˜1420) of bright RVS F-G-K standard stars will be used for the Radial Velocity Zero Point (RVZP) of the RVS. These standard stars have been observed on the ground with the Sophie, Coralie and Narval spectrometers, and their Spectroscopic Radial Velocities (SRVs) have been published by Soubiran et al. (2013). These SRVs are not Kinematic Radial Velocities (KRVs) which are what we need for studies of galatic dynamics. However in this paper we show that these SRVs are well suited to establish the Radial Velocity Zero Point of the Gaia RVS, provided that CU6 pipelines of the DPAC such as Calibration of the RVS (DU630) and Determination of RVs by cross-correlation with templates (DU650 STA) really use wavelength lines and spectra computed with 3D hydrodynamical model atmospheres, which conveniently treat the convective shifts. Final SRVs given by the Gaia CU6 pipelines and later published in the Gaia final catalogue would then only be corrected from the gravitational shift by the DPAC CU8 in order to become true KRVs.