Line formation in the wind of alf Cyg.

Abstract

In the considered investigation, the method reported by Mihalas et al. (1976) is used to search for plausible atmospheric models for Alpha Cyg and to find limits on its mass-loss rate. Assumptions about the wind and underlying photosphere, and the free parameters of the model are described. The best-suited numerical method is discussed and possible mechanisms of line formation in the wind of Alpha Cyg are examined, taking into account their plausibility. Synthetic profiles for several models are compared with the observed profile of Mg II lambda 2802 in Alpha Cyg. The application of an accurate NLTE method for calculating synthetic profiles for spherically symmetric models of expanding atmospheres makes it possible to find a range of atmospheric structures which yield profiles resembling those from IUE observations of double-lambda 2795, 2802 in Alpha Cyg. Two mechanisms are successful, but only one is physically consistent for an A-type star.