Mg line formation in late-type stellar atmospheres I. The model atom

• Published in: Astronomy and astrophysics (Berlin) Vol. 579; p. A53
• Main Authors: Osorio, Y., Barklem, P. S., Lind, K., Belyaev, A. K., Spielfiedel, A., Guitou, M., Feautrier, N.
• Format: Journal Article
• Language: English
• Published: 01.07.2015
• Subjects: Astronomy; atomic data; Collision dynamics; Construction; Formations; Fysik med inriktning mot astrofysik; Inelastic collisions; Line: formation; Magnesium; Mathematical models; Physics with specialization in Astrophysics; Stars; stellar abundances
• ISSN: 0004-6361; 1432-0746; 1432-0746
• DOI: 10.1051/0004-6361/201525846

Magnesium is an element of significant astrophysical importance, often traced in late-type stars using lines of neutral magnesium, which is expected to be subject to departures from local thermodynamic equilibrium (LTE). In this paper we build and test a Mg model atom for spectral line formation in late-type stars with new or recent inelastic collision data and no associated free parameters. We aim to reduce these uncertainties and thereby improve the accuracy of Mg non-LTE modeling in late-type stars. For the low-lying states of Mg [subI], electron collision data were calculated using the R-matrix method. Our results emphasize the need for accurate data of Mg collisions with both electrons and H atoms for precise non-LTE predictions of stellar spectra, but demonstrate that such data can be calculated and that ab initio non-LTE modeling without resort to free parameters is possible. Grids of departure coefficients and abundance corrections for a range of stellar parameters are planned for a forthcoming paper.