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J. R. Busche (Wheeling Jesuit University), D. J. Hillier (University of Pittsburgh)
Rotation can have a marked impact on the density and velocity structure in a stellar atmosphere. Using a newly developed formal solution code and a semi-analytic model for the effects of rotation on the wind structure, we investigate the various effects of rotation on line profiles, including the classical Doppler broadening, the resonance zone effect (RZE), and the density enhancement effect (\rho effect). Non-photospheric lines formed in extended optically thick atmospheres do not show just the simple classical line broadening. In such cases the traditional method of convolving the line profile with a rotation profile is insufficient. To handle these situations, we start with a sophisticated 1-D model of a stellar atmosphere, and use a 2-D observers frame code to calculate the observed effect on line profiles under various assumptions about the 2-dimensional velocity field and density distribution. Importantly, the code handles arbitrary line profiles and line blends. Because it should be a small effect, rotational distortion of the stellar surface is ignored. Gravity darkening is also not handled at this time.
We apply the code to a model for the SMC~O7Iaf supergiant AV83, and examine the influence on rotation on line profiles in both the UV and optical. We also use the code to infer a rotation rate of 40-50km s-1 for the LBV P~Cygni which is consistent with earlier estimates. We find that the RZE can have a significant influence on the profile shape, while the \rho effect primarily influences the line strength. These affect the quality of the spectroscopic fits to the data, and consequently the derived velocity field and other stellar parameters might be significantly biased for rapidly rotating stars with extended winds. We find that mass loss rates based upon the H\alpha line have systematic uncertainties of at least 10% for models with an equatorial density enhancement of a factor of two. These effects are larger in more extreme cases.
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.