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V. V. Dwarkadas, S. P. Owocki (Bartol Research Institute, Univ of Delaware)
Nebulae around Luminous Blue Variable (LBV) stars are characterized by asymmetric, often bipolar shapes. A classic example is the Homunculus nebula around the massive star \eta Carinae. In the standard interpretation of the generalized interacting stellar winds models, the asymmetry in shape is attributed to an asymmetry in the density structure of the ambient medium. However the observational evidence does not support this. In this work we use scaling relations derived from the theory of radiatively driven winds to model the outflows from LBV stars. Rotation of the star, and the latitudinal variation of the stellar flux due to gravity darkening is taken into account. It is shown that a star rotating close to its critical velocity will emit a wind whose velocity is higher at the poles than the equator, which can give rise to an asymmetric, bipolar wind-blown nebula. Inclusion of gravity darkening shifts the relative density toward the poles, but does not change the overall shape of the interaction front. We discuss the implications of these results for the general formation of wind-blown nebulae.
VVD is supported by NASA grant NAG5-3530, and by a grant from NASA administered by the American Astronomical Society.
The author(s) of this abstract have provided an email address for comments about the abstract: vikram@bartol.udel.edu