EDP Sciences
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Volume 390, Number 3, August II 2002
Page(s) 1141 - 1152
Section Physical and chemical processes
DOI http://dx.doi.org/10.1051/0004-6361:20020723

A&A 390, 1141-1152 (2002)
DOI: 10.1051/0004-6361:20020723

The diffusion of radiation in moving media

III. Stochastic representation of spectral lines
R. Wehrse1, 2, B. Baschek1 and W. von Waldenfels3, 2

1  Institut für Theoretische Astrophysik, Tiergartenstrasse 15, 69121 Heidelberg, Germany
2  Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Im Neuenheimer Feld 368, 69120 Heidelberg, Germany
3  Institut für Angewandte Mathematik, Im Neuenheimer Feld 294, 69120 Heidelberg, Germany

(Received 11 January 2002 / Accepted 15 May 2002)

In this paper we present analytical expressions for the radiative flux, the effective extinction coefficient, and the radiative acceleration deep inside a differentially moving, very optically thick medium with many spectral lines. It is shown that the line contribution is essentially given by the characteristic function of wavelength averages of the extinction coefficient. It can be calculated either by means of the generalized opacity distribution function or by means of a Poisson point process model. Several examples are given to demonstrate the basic consequences of line densities, widths, and strengths, as well as velocity gradients on the diffusive flux. We demonstrate that for Poisson distributed lines the diffusive flux decreases with increasing absolute values of the velocity gradient (i.e. that the flux has a maximum for static media), and that such lines have hardly a direct influence on the radiative acceleration.

Key words: diffusion -- radiative transfer -- stars: interiors -- novae, cataclysmic variables -- supernovae: general

Offprint request: R. Wehrse, wehrse@ita.uni-heidelberg.de

© ESO 2002