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J. P. Aufdenberg (Arizona State U.), P. H. Hauschildt (U. Georgia), E. Baron (U. Oklahoma)
We present non-LTE metal line-blanketed stellar wind atmosphere models and synthetic spectra for comparison with the spectral energy distribution of the A-supergiant Deneb from UV to radio wavelengths. Deneb is alone among A-supergiants in having both a precisely measured angular diameter from the Navy Prototype Optical Interferometer (Nordgren, T. et al., 1999, priv. comm.) and a positive detection at centimeter wavelengths with the Very Large Array (Howarth, I., 1999, priv. comm.). These recent measurements together with our wind atmosphere models considerably improve constraints on Deneb's fundamental stellar and wind parameters. Using the precise angular diameter we are able to use the Barnes-Evans relationship to constrain the reddening toward Deneb independent of any assumptions about its intrinsic colors. Our models treat the hydrostatic inner atmosphere and the extended expanding outer atmosphere as a unified structure and the radiative transfer is solved in the co-moving frame. We present synthetic radio spectra for the partially ionized winds of A-supergiants over a range of mass-loss rates and we find that the standard assumptions regarding the radio spectra of warm supergiants break down for A-supergiants. By simultaneously fitting the UV, optical, IR and radio spectrophotometry we are able to constrain the mass-loss rate and temperature distribution throughout the extended atmosphere. Stability of the deep hydrostatic layers against outward acceleration provides a lower limit on gravitational acceleration in these layers.
This work was supported in part by an Arizona State University NASA Space Grant Fellowship and CNRS, NSF, and NASA grants to the University of Georgia. Some calculations were performed on the IBM SP and the SGI Origin 2000 of the UGA UCNS and on the IBM SP at SDSC and on the Cray T3E of the NERSC.