LINE-PROFILE VARIATIONS FROM ATMOSPHERIC ECLIPSES - CONSTRAINTS ON THE WIND STRUCTURE IN WOLF-RAYET STARS

Binary systems in which one of the components has a stellar wind may p resent a phenomenon known as ''wind'' or ''atmospheric eclipse,'' in w hich that wind occults the luminous disk of the companion. The enhance d absorption profile, relative to the spectrum at uneclipsed orbital p hases, can be modeled to yield constraints on the spatial structure of the eclipsing wind. A new, very efficient approach to the radiative t ransfer problem, which makes no requirements with respect to monotonic ity of the velocity gradient or the size of that gradient, is presente d. The technique recovers both the comoving frame calculation and the Sobolev approximation in the appropriate limits. Sample computer simul ations of the line profile variations induced by wind eclipses are pre sented. It is shown that the location of the wind absorption features in frequency is a diagnostic tool for identifying the size of the wind acceleration region. Comparison of the model profile variations with the observed variations in the W-R+6 binary system V444 Cyg illustrate how the method can be used to derive information on the structure of the wind of the W-R star and constrain the size of the W-R core radius .