WIND VARIABILITY OF B-SUPERGIANT .2. THE 2-COMPONENT STELLAR WIND OF GAMMA-ARAE

The stellar wind of the rapidly rotating early-B supergiant, gamma Ara , is studied using time series, high-resolution IUE spectroscopy secur ed over similar to 6 days in 1993 March. Results are presented based o n an analysis of several line species, including N V, C IV, Si IV, Si III, C II, and Al III. Comparisons of the time-averaged wind line morp hology of gamma Ara to the UV spectra of other OB stars, and to profil es from spherically symmetric wind models, suggest that the wind of ga mma Ara is equatorially enhanced. Co-existing time variable features a re identified at low-velocity (redward of similar to 750 km s(-1)) and at higher-speeds extending to similar to -1500 km s(-1). The observed interface between these structures is 'defined' by the appearance of a discrete absorption component which is extremely sharp (in velocity space). The central velocity of this 'Super DAC' changes only graduall y, over several days, between similar to -400 and -750 km s(-1) in mos t of the ions. However, its location is shifted redward by almost 400 km s(-1) in Al III and C II, indicating that the physical structure gi ving rise to this feature has a substantial velocity and ionization ju mp. Constraints on the relative ionization properties of the wind stru ctures are discussed. The overall wind activity in gamma Ara exhibits a clear ion dependence, such that low-speed features are promoted in l ow-ionization species, including Al III, C II, and Si III. We also hig hlight that - in contrast to most OB stars - there are substantial dif ferences in the epoch-to-epoch time-averaged wind profiles of gamma Ar a and that the high-speed component observed during our 1993 time seri es is normally not present. We discuss the potential roles of the radi ative bi-stability mechanism and wind compressed regions due to rapid stellar rotation for providing gross wind distortions in gamma Ara.