Wind variability of B supergiants II. The two-component stellar wind of γ Arae

The stellar wind of the rapidly rotating early-B supergiant, γAra, is studied using time series, high-resolution IUE spectroscopy secured over∼ 6 days in 1993March. Results are presented based on an analysis of several line species, including N v, C iv, Si iv, Si iii, C ii, and Al iii. Comparisons of the timeaveraged wind line morphology of γ Ara to the UV spectra of other OB stars, and to profiles from spherically symmetric wind models, suggest that the wind of γ Ara is equatorially enhanced. Co-existing time variable features are identified at lowvelocity (redward of ∼ 750 km s−1) and at higher-speeds extending 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 gradually, over several days, between ∼ −400 and −750 km s−1 in most 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 giving rise to this feature has a substantial velocity and ionization jump. Constraints on the relative ionization properties of the wind structures are discussed. The overall wind activity in γ Ara exhibits a clear ion dependence, such that low-speed features are promoted in low-ionization species, including Al iii, C ii, and Si iii. We also highlight that – in contrast to most OB stars – there are substantial differences in the epoch-to-epoch time-averaged wind profiles of γ Ara and that the high-speed component observed during our 1993 time series is normally not present. We discuss the potential roles of the radiative bi-stability mechanism and wind compressed regions due to rapid stellar rotation for providing gross wind distortions in γ Ara.