Redistribution effects on line formation in moving stellar atmospheres

The effects of photon frequency and angular redistribution arising from pure Doppler (Rsub(I)), Doppler with natural line broadening (Rsub(II)) and from the combined Doppler, natural and collisional line broadening (Rsub(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 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 (Astron. and Astrophysics.; 35:233 (1974)). 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. (author)