Radiative transfer in atmospheres with spherical symmetry

A new approximate method to solve the time-independent transfer equation in a system with spherical geometry is presented. No restriction is imposed on the radial variation of the opacity so that the method is applicable even when the opacity is tabulated. The approximation consists in solving the transfer equation only for the outward and inward radial directions and in using the corresponding intensities for the numerical computation of the mean intensity and flux. To obtain the integration weights, we make several hypotheses on the directional dependence of the intensity, taking into account the principal properties of radiation transfer in spherical symmetric systems. We point out the parallelism that exists between this approximation for spherical geometry and a similar one for the plane-parallel case. Results are presented for the conservative and non-conservative cases, and they are compared to those of other authors.