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Astron. Astrophys. 332, 732-738 (1998)

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Resonance scattering of Lyman alpha from interstellar hydrogen

Mats Braskén and Erkki Kyrölä

1 Åbo Akademi University, Department of Physics, Porthansgatan 3, FIN-20500 Åbo, Finland
2 Finnish Meteorological Institute, Geophysical Research Division, P.O. Box 503, FIN-00101 Helsinki, Finland

Received 20 June 1996 / Accepted 12 December 1997

Abstract

We derive a set of new line-of-sight (LOS) integrals and phase functions for the resonance scattering of unpolarized Lyman [FORMULA] light in the optically thin medium limit. To explicitly show the approximations done, and to indicate the range of validity of previously published formulas, we start by treating the general theory of resonance scattering. For broad band Ly [FORMULA] and a hot gas the resulting LOS integral can be evaluated analytically. This is the case for Ly [FORMULA] light from the sun scattering off neutral interstellar hydrogen. The ground state populations of the hydrogen atom will effect the value of the scattered intensity. Two population distributions are considered: a thermal equilibrium population and a population established by the atom-light interaction.

Key words: atomic processes – scattering – ISM: general – polarization

Send offprint requests to: M. Braskén

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© European Southern Observatory (ESO) 1998

Online publication: March 23, 1998
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