A domain decomposition approach for radiation transport in astrophysical dust envelopes

Abstract

A spatial domain decomposition method is presented for computing the continuum transfer of radiation associated with luminous astrophysical sources, embedded in extended clouds, in which dust gives rise to a substantial opacity. The method is relevant to the modelling of protostars, evolved stars, galaxies, and active galactic nuclei. Different transport algorithms are used in each subdomain. The algorithms are each specialized to handle conditions of high or low opacity, and internal opacity boundaries. Grid cell spacing can be adjusted to efficiently resolve variation in the radiation field on different length scales. The method is applied to a set of test problems in which a central point source and a thin, luminous accretion disk are enclosed in an envelope. A simple two-group wavelength approximation is used, representing optical and thermal radiation. Group opacities drop to zero at the dust vaporization temperature. Domain decomposition computations are first checked against a semi-analytic solution to the diffusion approximation for spherically symmetric problems. The method is then applied to more realistic axisymmetric problems to compute the temperature structure of the envelope and accretion disk surface, and the location of the dust destruction front.