Disk Formation in Rotating Wolf-Rayet Stellar Winds

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Session 31 -- Massive Hot Stars

[31.09] Disk Formation in Rotating Wolf-Rayet Stellar Winds

R. Ignace, J.P. Cassinelli, and J.E. Bjorkman (University of Wisconsin-Madison)

There is considerable evidence that many evolved massive stars are intrinsically aspherical from observations of polarization or of nebulae surrounding some Wolf-Rayet stars and Luminous Blue Variables. The observations indicate axisymmetry, suggesting that rotation may be important. We apply to Wolf-Rayet Stars the Wind-Compressed Disk (WCD) model that was developed by Bjorkman \& Cassinelli (1993) for Be stars. In this model there is a flow of material from the polar regions of the wind towards the equatorial plane as a result of the rotation. The formation of a disk becomes more likely as the radiation-driven polar wind is accelerated more slowly. Although the winds of Wolf-Rayet stars tend to reach higher terminal velocities than is the case for the Be stars, there can still be significant flow towards the equator because of the gradual acceleration that has been inferred for the Wolf-Rayet winds. We discuss the conditions for equatorial compression to be important for Wolf-Rayet stars and present a possible explanation for the fact that not all Wolf-Rayet stars show intrinsic polarization or other evidence for equatorial density enhancement. Bipolar winds from stars that are thought to be precursors to the Wolf-Rayet phase of evolution are also discussed in the context of the WCD model.

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