We have computed theoretical He II λ4686 emission line profiles for Friend and Castor's focused stellar wind model for the HDE 226868 = Cyg X-1 system. These were added to theoretical photospheric profiles and compared to the observed profiles. The composite profiles reproduce most of the significant features of the variations of the observed profiles if the visible star is close to filling its Roche lobe.
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Gies et al. (1986) studied this question.
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