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J. P. Aufdenberg (Harvard-Smithsonian CfA)
Spherical, hydrostatic, non-local thermodynamic equilibrium (non-LTE) metal line-blanketed model atmospheres have been employed to reproduce the spectral energy distributions of the bright B-type giant stars Beta and Epsilon Canis Majoris, including the extreme ultraviolet where previous models have failed. (Aufdenberg, J.P., et al. 1999, MNRAS, 302, 599; Aufdenberg, J.P. et al., 1998, ApJ, 498, 837). The combination of spherical geometry and line-blanketing produces significantly different model temperature structures and synthetic extreme ultraviolet spectra relative to otherwise similar plane-parallel geometry models. In addition, a full grid of O- and early B-type model stellar atmospheres has been constructed and comparisons with hydrostatic, plane-parallel, LTE line-blanketed models show that our models predict consistently higher ionizing fluxes, particularly at lower effective temperatures.
Models for hot, luminous stars and their winds have been developed which unify the inner hydrostatic layers with the outer dynamic layers of the atmosphere into a single structure. These models include the effects of full non-LTE metal line-blanketing in both the computation of the model atmosphere plus wind and the synthetic spectrum. Models of this type have been developed for comparison with the spectral energy distribution and detailed spectrum of the A-type supergiant Deneb. Synthetic spectra have been computed which are able to match reasonably well Deneb's observed spectral energy distribution between 120 nm to 3.6 cm. These models predict that Deneb's expanding envelope is only partially ionized, which leads to a steeper spectral slope at millimeter and radio wavelengths than predicted by a fully ionized model commonly applied to hotter O- and B-type stars. Non-LTE model structures and line formation in the ultraviolet indicate mass-loss rates 50 times larger than in our LTE studies.
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The author(s) of this abstract have provided an email address for comments about the abstract: jaufdenberg@cfa.harvard.edu