Redistribution effects on line formation in moving stellar atmospheres—II. The non-isotropic redistribution functions RI,II,III(x′,n′; x,n)

The effects of photon frequency and angular redistribution arising from pure Doppler (R_I), Doppler with natural line broadening R_II and from the combined Doppler, natural and collisional line broadening (R_III) are examined for line formation in plane-parallel semi-infinite and slab differentially expanding atmospheres. Line source functions and their corresponding emergent line intensities are obtained using the full angle-dependent redistribution functions. The results are compared with those obtained assuming complete redistribution and also with those using two types of angle-averaged redistribution functions; those angle-averaged in the observer's rest frame and those angle-averaged in the fluid frame. It is found that the redistribution functions angle-averaged in the observer's rest frame can produce spurious effects on line formation in moving media, as pointed out by Magnan.¹ On the other hand, emergent line intensities obtained using the redistribution functions angle-averaged in the fluid frame are found to differ by little from those obtained using the full angle-dependent redistribution functions, for the velocity fields considered here.