Multilevel line formation in the expanding envelope of zeta Aur/VV CEP systems.

Abstract

The Sobolev method is the basis of the present multilevel formalism for UV line profiles in Zeta Aur systems; atomic models for Si II and Fe II UV multiplet 9 and 191 are used to study problems implicated in the two-level approximation. The first Si II model encompasses 11 composite levels together with two continua, and all possible interlocking effects are considered with 12 bound-bound transitions. A second model investigates the effects of radiative pumping on the population of the doublet fine structure levels of the Si II ground state, with computations showing significant consequences for the resulting emission part of the P Cygni profiles. Attention is also given to the radiative pumping of the Mult. 9/Mult. 191 mechanism with a simple eight-level model.