AAS Meeting #193 - Austin, Texas, January 1999
Session 44. Modeling Stellar Characteristics
Display, Thursday, January 7, 1999, 9:20am-6:30pm, Exhibits Hall 1

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[44.03] Modeling the UV/Optical Energy Distributions of the B Stars

E.L. Fitzpatrick (Villanova University), D. Massa (Raytheon STX)

We describe the initial results from a program whose goals are: 1) to test quantitatively the level of agreement between the theoretical stellar energy distributions predicted by the current generation of line-blanketed model atmospheres (the ATLAS9 models from R.L. Kurucz) and the observed UV/optical energy distributions of the main sequence B stars; and 2) to determine how precisely and accurately the stellar properties (effective temperature, surface gravity, metallicity, and microturbulence velocity) can be determined from analyses of the stellar continua.

We demonstrate that the ATLAS9 models can reproduce the observed UV/optical continua of unreddened main sequence B stars to a level consistent with the uncertainties in currently available spectrophotometric data. This success is due to a number of factors, including 1) the quality of the ATLAS9 models; 2) the excellent absolute UV/Optical flux calibration produced for the Faint Object Spectrograph aboard the HST; 3) the expansion of the original Kurucz model grid to a wide range of temperatures, gravities, metallicities, and microturbulence velocities; and 4) the use of non-linear fitting techniques to optimize all of the model parameters simultaneously. Further, we show that both the model atmosphere parameters AND the shape of the UV/optical interstellar extinction curve can be extracted from analysis of UV/optical spectra of reddened stars. This is possible because the spectral ``signature'' of interstellar extinction is very different from the ``signatures'' of temperature, surface gravity, metallicity, and microturbulence.

The quality of the agreement between theory and observation is illustrated for a number of Galactic stars with effective temperatures between about 9600 K and 28000 K. The data for these stars include HST and IUE observations and ground-based optical photometry and spectrophotometry.

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