2013A&A...550A..28M

Magnesium abundances of cool stars with different metallicities are important for understanding the galactic chemical evolution. This study tests atomic data used in stellar magnesium abundance analyses. We evaluate nonlocal thermodynamical equilibrium (NLTE) line formation for MgI, using the most up-to-date theoretical and experimental atomic data available so far, and check the Mg abundances from individual lines in the Sun, four well studied A-type stars, and three reference metal-poor stars. With the adopted gf-values, NLTE abundances derived from the MgI 4703Å, 5528Å, and MgIb lines are consistent within 0.05 dex for each A-type star. The same four MgI lines in the solar spectrum give consistent NLTE abundances at logN_Mg/N_H=-4.45, when correcting van der Waals damping constants inferred from the perturbation theory. Inelastic Mg+H collisions as treated by Barklem, Belyaev, Spielfiedel, Guitou, and Feautrier serve as an efficient thermalizing process for the statistical equilibrium of MgI in the atmospheres of metal-poor stars. The use of Mg+H collision data improves Mg abundance determinations for HD84937 and HD122563, though it does not completely remove the differences between different lines.