Non-Lte Transfer -- II TWO-LEVEL ATOMS WITH STOCHASTIC VELOCITY FIELD

Following previous work on L TE stochastic transfer (Auvergne et al.; Frisch), transfer with incoherent scattering is considered for two-level atoms in the presence of turbulent velocity fields with finite eddy-size. Assuming that the velocity along each individual photon path may be represented by a Markov Process in time, we obtain a non-stochastic equation of transfer for the ‘ mean conditional intensity ’, from which the mean (observable) intensity may be recovered by integration over the velocity distribution. An integral equation of the Wiener–Hopf type is obtained for the ‘mean conditional source function ’ from which it is shown by techniques introduced in Paper I (Frisch & Frisch) that the rms surface source function assumes the usual value $$\sqrt{}\,\epsilon B$$ for uniform thermal source B. An ‘effective kernel and source function ’ approximation is introduced by which a standard transfer problem is recovered and worked out explicitly in a special case. It is shown that finite eddy-size effects can change the effective source function and the emergent profile by a factor 2 or more.