We studied the circumstellar gas in Algol (β Persei) by analysing Hαdifference profiles (observed profiles minus composite theoretical (LTE) photospheric absorption line profiles of the stars), at 98 phases in the binary’s orbit (cf. Richards 1986, Ph.D. thesis, University of Toronto). The data were obtained from Sept. 1976 to Dec. 1977; with an average phase interval of 0.02 over the entire orbit.

There was a smooth change in the profiles from strong, redshifted emission just outside primary eclipse, to an almost flat profile at mid-secondary eclipse, to strong, blueshifted emission just before primary eclipse began. Absorption was detected throughout primary eclipse, and there were smooth transitions between pure absorption and pure emission. The emission and absorption had FWHM’s of ~200 km s−1 and ~200 to 450 km s−1, respectively; with line strengths up to 10% and 19% of the continuum, respectively.