Model estimates of inelastic calcium-hydrogen collision data for non-LTE stellar atmospheres modeling⋆
1 LERMA, Observatoire de Paris, Sorbonne Université, UPMC Univ. Paris 06, CNRS-UMR 8112, 92195 Meudon, France
2 Department of Theoretical Physics and Astronomy, Herzen University, Moika 48, 191186 St. Petersburg, Russia
3 Université Paris-Est, Laboratoire Modélisation et Simulation Multi-Echelle, UMR 8208 CNRS, 5 Bd Descartes, Champs-sur-Marne, 77454 Marne la Vallée, France
Received: 27 October 2015
Accepted: 12 January 2016
Aims. Inelastic processes in low-energy Ca + H and Ca+ + H− collisions are treated for the states from the ground state up to the ionic state with the aim to provide rate coefficients needed for non-LTE modeling of Ca in cool stellar atmospheres.
Methods. The electronic molecular structure was determined using a recently proposed model approach that is based on an asymptotic method. Nonadiabatic nuclear dynamics were treated by means of multichannel formulas, based on the Landau-Zener model for nonadiabatic transition probabilities.
Results. The cross sections and rate coefficients for inelastic processes in Ca + H and Ca+ + H− collisions were calculated for all transitions between 17 low-lying covalent states plus the ionic state. It is shown that the highest rate coefficient values correspond to the excitation, de-excitation, ion-pair formation, and mutual neutralization processes involving the Ca(4s5s 1,3S) and the ionic Ca+ + H− states. The next group with the second highest rate coefficients includes the processes involving the Ca(4s5p 1,3P), Ca(4s4d 1,3D), and Ca(4s4p 1P) states. The processes from these two groups are likely to be important for non-LTE modeling.
Key words: atomic data / line: formation / stars: abundances
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