NLTE abundances of Mn in a sample of metal-poor stars

摘要

Aims. Following our solar work, we perform NLTE calculations of the Mn abundance for fourteen stars with Fe/H from 0 to -2.5, mainly to show how NLTE affects Mn abundances in cool stars of different metallicities. Methods. The spectrum synthesis and Mn abundances are based on statistical equilibrium calculations using various estimates for the influence of hydrogen collisions. Results. The NLTE abundances of Mn in all studied stars are systematically higher than the LTE abundances. At low metallicities, the NLTE abundance corrections may run up to 0.5-0.7 dex. Instead of a strong depletion of Mn relative to Fe in metal-poor stars as found by the other authors, we only find slightly subsolar values of Mn/Fe throughout the range of metallicities analyzed here. Conclusions. The Mn/Fe trend in metal-poor stars is inconsistent with the predictions of galactic chemical evolution models, where Mn is less produced than Fe.