Research Note

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
e-mail: andrey.k.belyaev@gmail.com
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

Abstract

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.