RADIATIVE-TRANSFER IN A CLUMPY MEDIUM .2. THE MEGA-GRAINS APPROXIMATION FOR 2-PHASE MODELS

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 'mega-grains', 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.