On inelastic hydrogen atom collisions in stellar atmospheres

Abstract

The influence of inelastic hydrogen atom collisions on non-LTE spectral line formation has been, and remains to be, a significant source of uncertainty for stellar abundance analyses, due to the difficulty in obtaining accurate data for low-energy atomic collisions either experimentally or theoretically. For lack of a better alternative, the classical "Drawin formula" is often used. Over recent decades, our understanding of these collisions has improved markedly, predominantly through a number of detailed quantum mechanical calculations. In this paper, the Drawin formula is compared with the quantum mechanical calculations both in terms of the underlying physics and the resulting rate coefficients. It is shown that the Drawin formula does not contain the essential physics behind direct excitation by H atom collisions, the important physical mechanism being quantum mechanical in character. Quantitatively, the Drawin formula compares poorly with the results of the available quantum mechanical calculations, usually significantly overestimating the collision rates by amounts that vary markedly between transitions.

9 pages, 6 figures, accepted for A&A

References in corpus (3)

• Non-LTE calculations for neutral Na in late-type stars using improved atomic data
• Inelastic Na+H collision data for non-LTE applications in stellar atmospheres
• Revised Born-Oppenheimer approach and a multielectron reprojection method for inelastic collisions

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