Abstract
ζ Aur binaries are particularly well suited for the study of the winds of late type supergiants. The analysis technique is based on theoretical modelling of flux profiles which are formed by resonance scattering in the expanding envelope. However, the hot B star ionizes the wind and can produce a considerable H II region around the B star. In order to investigate the influence of the Stromgren sphere on the line formation we have calculated theoretical P Cyg line profiles with an H II region. The line source function is solved with the Sobolev method followed by a correct formal integration (Hempe, 1982). The ionization of metals within the H II region is described by an ionization parameter which mimics the typical ionization fraction of the relevant ions. The resulting line profiles are dependent on the geometric shape of the H II region, the velocity distribution, and the opacity parameter. The reduced absorber density within the H II region produces weakened line profiles and the specific geometry of the H II region influences the emission and the absorption component in different ways. The careful analysis of model computations suggests that the region of the line formation is not only restricted to the vicinity of the B star, hence the outer integration boundary has to be taken to a sufficiently large radius in the calculation of line profiles.
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