Radiative transfer in an expanding spherical medium

Abstract

We describe a method for solving the transfer equation of a spectral line in statistical equilibrium with a background continuum; the atmosphere may be static or expanding and have plane or spherical symmetry. The method permits the rapid and accurate solution of line transfer problems in media with given gross structure. The basic approach is to separate the calculation into two parts: the accurate determination of the error with which an assumed, or an iterated, solution satisfies the conservation equations of statistical equilibrium; and the calculation of corrections by means of an approximate operator. The method combines differential as well as integral equations.