Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aspc..355...65o&link_type=abstract
Stars with the B[e] Phenomenon. ASP Conference Series, Vol. 355, Proceedings of the Conference Held 10-16 July, 2005, at the Isl
Astronomy and Astrophysics
Astronomy
1
Scientific paper
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 supergiant B[e] stars.
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