Absorption-line profiles in a companion spectrum of a mass-losing cool supergiant

Cool star winds can best be observed in resonance absorption lines seen in the spectrum of a hot companion, due to the wind passing in front of the blue star. We calculate absorption-line profiles that will be seen in the ultraviolet part of the blue companion spectrum. Line profiles are derived for different radial dependences of the cool star wind and for different orbital phases of the binary. Bowen & Willson (1986) find theoretically that stellar pulsations drive mass loss. We therefore apply our calculations to the Cepheid binary S Muscae which has a B5 V companion. We find an upper limit for the Cepheid mass loss of Ṁ ≤ 7 x 10^-10 M_⊙ per year provided that the stellar wind of the companion does not influence the Cepheid wind at large distances.