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Wind variability of B supergiants
II. The two-component stellar wind of Arae
R.K. Prinja 1,
D. Massa 2,
A.W. Fullerton 3,
I.D. Howarth 1 and
M. Pontefract 1
Received 14 March 1996 / Accepted 17 June 1996
The stellar wind of the rapidly rotating early-B supergiant, Ara, is studied using time series, high-resolution IUE spectroscopy secured over days in 1993 March. 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 time-averaged wind line morphology of Ara to the UV spectra of other OB stars, and to profiles from spherically symmetric wind models, suggest that the wind of Ara is equatorially enhanced.
Co-existing time variable features are identified at low-velocity (redward of km s-1) and at higher-speeds extending to 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 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 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 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 Ara.
Key words: line: profiles stars: early-type stars: individual (HD 157246) stars: mass loss
Send offprint requests to: R.K. Prinja
Online publication: July 8, 1998