AAS 197, January 2001
Session 8. Circumstellar Matter and Winds
Display, Monday, January 8, 2001, 9:30am-7:00pm, Exhibit Hall

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[8.11] Multiple Critical Points and Solutions for Rotating Line-Driven Stellar Winds

J.E. Bjorkman (U Toledo), A.V. Moorhead (U Arizona)

Mass loss from luminous early-type stars occurs via line-driven stellar winds (Castor, Abbott, & Klein 1975; hereafter CAK). By quasi-linearizing the CAK wind equation, Bjorkman (1995) was able to perform a full critical point analysis to systematically determine all possible outflow solutions. This analysis showed that for a CAK point source wind, there was only one outflow solution with an X-type critical point. However, Bjorkman did not include the finite disk correction factor nor did he include rotation. In the present study, we add rotation and the finite disk correction factor to the CAK wind equation. We find that for a stellar point source, the addition of rotation has little effect on the allowed solution. In contrast, the finite-disk CAK equation produces quite varied solution topologies as the rotation rate is increased, eliminating some critical points while creating others. In particular, we find at high rotation rates that the inner X-type critical point vanishes, while new X-type critical points appear at large radii. In addition, the CAK wind equation has two solutions for the velocity, which leads to a doubling of the number of critical points (up to 10 total). Most importantly, multiple X-type critical points are found that satisfy the boundary conditions. This results in multiple outflow solutions for the star, leading to the possibility of multiple mass loss rates. Depending on the unknown time-dependent stability of these solutions, we conclude that it may be possible for a star to switch between high and low mass loss states. This effect could explain the notorious variability of Be stars, where it is observed that the wind can switch on and off as a function of time. Similarly, the outer critical point solutions have lower wind speeds, which offers the possibility that outer solution could lead to disk formation, while the inner solution does not. Thus the multiple wind solutions provide a potential mechanism for explaining the occasional disappearance of the disks around Be stars. This work has been supported under NASA grant NAG5-3248 to the University of Toledo.

The author(s) of this abstract have provided an email address for comments about the abstract: jon@physics.utoledo.edu

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