Radiative transfer in a clumpy medium - II. The mega-grains approximation for two-phase models

Abstract

An approximate method is presented for describing the transfer of radiation inside a two-phase medium. The medium is assumed to consist of spherical clumps, with uniform size and density, embedded in a more tenuous interclump medium. The transfer of radiation is modelled by treating the clumps as large grains, or ‘megagrains’, with absorption and scattering coefficients calculable from the properties of the dust grains of which the clumps are composed. Numerical examples, for various two-phase slabs, show that radiation intensities calculated in this way agree closely with those found by modelling the density variations as a two-state Markov process.