H atom collisions
we use Drawin approximation criticized by this paper
On inelastic hydrogen atom collisions in stellar atmospheres
Barklem, P. S., Belyaev, A. K., Guitou, M., Feautrier, N., Gadéa, F. X., & Spielfiedel, A.
2011, Astronomy and Astrophysics, 530, A94
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.
KEYWORDS: atomic data, line: formation, stars: abundances, stars: atmospheres
REMOTE URL : http://dx.doi.org/10.1051/0004-6361/201116745
REMOTE URL : http://arxiv.org/abs/1104.1334
REMOTE URL : http://adsabs.harvard.edu/abs/2011A%26A...530A..94B
ADS URL : http://adsabs.harvard.edu/abs/2011A%26A...530A..94B
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