Session 43 - Variable Stars.
Display session, Thursday, January 08
Exhibit Hall,

## [43.04] The Mysterious Winds of the Main Sequence B Stars in NGC 6231

D. Massa (Hughes STX)

I will present new HST\/ GHRS observations of the extraordinary stellar winds of the main sequence B stars in NGC 6231. IUE\/ observations have shown that, unlike all normal main sequence B stars, the early B main sequence stars in the core of NGC 6231 all have well developed C \sc iv \lambda\lambda1550 wind lines (Massa, Savage, amp; Cassinelli 1984, ApJ, 284, 437).

Perhaps even more perplexing, is that the wind line profiles cannot be fit using normal velocity laws for the wind acceleration. One means of resolving this dilemma is to assume that the wind law for the NGC 6231 B stars is normal, but that it accelerates toward a terminal velocity which is much higher than the observed one. However, before the wind can attain its actual'' terminal velocity, it shocks and subsequently stalls'' at the observed terminal velocity. Such behavior is predicted by radiatively driven stellar wind theory for stars with weak winds (Springmann amp; Pauldrach 1994, Aamp;A, 262, 515). The new HST observations test some consequences of this conjecture.