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

¹ Max-Planck Institute for Astrophysics, Karl-Schwarzschild Str. 1, 85741 Garching, Germany
e-mail: mbergema@mpa-garching.mpg.de
² Landessternwarte, Königstuhl 12, 69117 Heidelberg, Germany
³ Department of Physics, Western Michigan University, Kalamazoo, MI 49008, USA

Received: 13 April 2012
Accepted: 5 July 2012

Abstract

We investigate the 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 ϵ = 2.93 ± 0.04 dex, in agreement with the meteorites. We present the grid of NLTE abundance corrections for Sr I and Sr II lines that covers a wide range of stellar parameters.