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| Paper: |
A Simple Nozzle Analysis of Slow-Acceleration Solutions in 1-D Models of Rotating Line-Driven Stellar Winds |
| Volume: |
355, Stars With the B[e] Phenomenon |
| Page: |
65 |
| Authors: |
Owocki, S. |
| Abstract: |
For a star rotating at more than about 75% of the critical rate, one-dimensional (1-D) models for the equatorial regions of a line-driven stellar wind show a sudden shift to a slow-acceleration solution, implying a slower, denser equatorial outflow that might be associated with the dense disks inferred for sgB[e] stars. To clarify the nature of this solution shift, I present here a simple analysis of the 1-D flow equations based on a nozzle analogy for the terms that constrain the local mass flux. At low rotation rates the nozzle minimum (or “throat”) occurs near the stellar surface, allowing a near-surface transition to a steeply accelerating, supercritical flow solution. But for rotations above about 75% of the critical rate, this local, inner nozzle minimum exceeds the global minimum approached asymptotically at large radii, implying that near-surface supercritical solutions would now have an overloaded mass loss rate. Maintaining a monotonically positive acceleration is then only possible if the flow is kept subcritical out to large radii, where the nozzle function approaches its absolute minimum. For fixed line-driving parameters, the associated enhancements in equatorial density are typically a factor 5-30 relative to the polar (or nonrotating) wind. However, when gravity darkening and 2-D flow effects are accounted for, it still seems unlikely that rotationally modified equatorial wind outflows could account for the very large densities inferred for the disks around B[e] supergiants. |
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