A DOMAIN DECOMPOSITION APPROACH FOR RADIATION TRANSPORT IN ASTROPHYSICAL DUST ENVELOPES

A spatial domain decomposition method is presented for computing the c ontinuum transfer of radiation associated with luminous astrophysical sources, embedded in extended clouds, in which dust gives rise to a su bstantial opacity. The method is relevant to the modelling of protosta rs, evolved stars, galaxies, and active galactic nuclei. Different tra nsport 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 r esolve variation in the radiation field on different length scales. Th e method is applied to a set of test problems in which a central point source and a luminous accretion disk are enclosed in an envelope A si mple two-group wavelength approximation is used, representing optical and thermal radiation. Group opacities drop to zero at the dust vapori zation temperature. Domain decomposition computations are first checke d against a semi-analytic solution to the diffusion approximation for spherically symmetric problems. The method is then applied to more rea listic axisymmetric problems to compute the temperature structure of t he envelope and accretion disk surface, and the location of the dust d estruction front. (C) 1998 Elsevier Science Ltd. All rights reserved.