**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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