A grid of non-local thermodynamic equilibrium corrections for magnesium and calcium in late-type giant and supergiant stars: application to Gaia

Abstract

We investigate NLTE effects for magnesium and calcium in the atmospheres of\nlate-type giant and supergiant stars. The aim of this paper is to provide a\ngrid of NLTE/LTE equivalent width ratios W/W* of Mg and Ca lines for the\nfollowing range of stellar parameters: Teff in [3500, 5250] K, log g in [0.5,\n2.0] dex and [Fe/H] in [-4.0, 0.5] dex. We use realistic model atoms with the\nbest physics available and taking into account the fine structure. The Mg and\nCa lines of interest are in optical and near IR ranges. A special interest\nconcerns the lines in the Gaia spectrograph (RVS) wavelength domain [8470,\n8740] A. The NLTE corrections are provided as function of stellar parameters in\nan electronic table as well as in a polynomial form for the Gaia/RVS lines.\n