Astronomy and Astrophysics – Astronomy
Scientific paper
May 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994ap%26ss.215..167k&link_type=abstract
Astrophysics and Space Science (ISSN 0004-640X), vol. 215, no. 2, p. 167-184
Astronomy and Astrophysics
Astronomy
B Stars, Binary Stars, H Ii Regions, Line Spectra, Spheres, Stellar Winds, Supergiant Stars, Ultraviolet Astronomy, Ultraviolet Spectra, Ionization, Mathematical Models, Opacity, Radiative Transfer, Stellar Envelopes, Stellar Evolution, Velocity Distribution
Scientific paper
Zeta Aur binaries are particularly well suited for the study of the winds of late type supergiants. The analysis technique is based on theoretical modeling 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 Stroemgren 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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