GSP-spec line list for the parametrisation of Gaia-RVS stellar spectra

Abstract

Context. The Gaia mission is a magnitude-limited whole-sky survey that collects an impressive quantity of astrometric, spectro-photometric and spectroscopic data. Among all the on-board instruments, the Radial Velocity Spectrometer (RVS) produces millions of spectra up to a magnitude of GRVS ~ 16. For the brightest RVS targets, stellar atmospheric parameters and individual chemical abundances are automatically estimated by the Generalized Stellar Parametriser – spectroscopy group (GSP-Spec). These data will be published with the third Gaia Data Release. Aims. Some major ingredients of the determination of these stellar parameters include the atomic and molecular line lists that are adopted to compute reference synthetic spectra, on which the parametrisation methods rely. We aim to build such a specific line list optimised for the analysis of RVS late-type star spectra. Methods. Starting from the Gaia-ESO line lists, we first compared the observed and synthetic spectra of six well-known reference late-type stars in the wavelength range covered by the RVS instrument. We then improved the quality of the atomic data for the transitions presenting the largest mismatches. Results. The new line list is found to produce very high-quality synthetic spectra for the tested reference stars and has thus been adopted within GSP-Spec. We note, however, that a couple of atomic line profiles, in particular the calcium infrared triplet lines, still show some deviations compared to the reference spectra, probably because of the adopted line-transfer assumptions (local thermodynamical equilibrium, hydrostatic, and no chromosphere). Future works should focus on such lines and should extend the present work towards OBA and M-type stellar spectra.