NLTE analysis of Sr lines in spectra of late-type stars with new R-matrix atomic data

M. Bergemann (1), C. J. Hansen (2), M. Bautista (3), and G. Ruchti (1) ((1) Max-Planck Institute for Astrophysics, Karl-Schwarzschild Str. 1, 85741, Garching, Germany; (2) Landessternwarte, K¨onigstuhl 12, 69117 Heidelberg, Germany; (3) Department of Physics, Western Michigan University, Kalamazoo, MI 49008, USA)

We investigate statistical equilibrium of neutral and singly-ionized strontium in late-type stellar atmospheres. Particular attention is given to the completeness of the model atom, which includes new energy levels, transition probabilities, photoionization and electron-impact excitation cross-sections computed with the R-matrix method. The NLTE model is applied to the analysis of Sr I and Sr II lines in the spectra of the Sun, Procyon, Arcturus, and HD 122563, showing a significant improvement in the ionization balance compared to LTE line formation calculations, which predict abundance discrepancies of up to 0.5 dex. The solar Sr abundance is log A = 2.93 \pm 0.04 dex, in agreement with the meteorites. A grid of NLTE abundance corrections for Sr I and Sr II lines covering a large range of stellar parameters is presented.


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