Determining the physical properties of the B stars. I. Methodology and first results

We describe a new approach to fitting the UV-to-optical spectra of B stars to model atmospheres and present initial results. Using a sample of lightly reddened stars, we demonstrate that the Kurucz model atmospheres can produ ce excellent fits to either combined low-dispersion IUE and optical photome try or HST FOS spectrophotometry, as long as the following conditions are f ulfilled: (1) an extended grid of Kurucz models is employed; (2) the IUE NE WSIPS data are placed on the FOS absolute flux system using the Massa & Fit zpatrick transformation; (3) and all of the model parameters and the effect s of interstellar extinction are solved for simultaneously. When these step s are taken, the temperatures, gravities, abundances, and microturbulence v elocities of lightly reddened B0-A0 V stars are determined to high precisio n. We also demonstrate that the same procedure can be used to fit the energ y distributions of stars that are reddened by any UV extinction curve that can be expressed by the Fitzpatrick & Massa parameterization scheme. We pre sent an initial set of results and verify our approach through comparisons with angular diameter measurements and the parameters derived for an eclips ing B-star binary. We demonstrate that the metallicity derived from the ATL AS9 fits to main-sequence B stars is essentially the Fe abundance. We find that a near zero microturbulence velocity provides the best fit to all but the hottest or most luminous stars (where it may become a surrogate for atm ospheric expansion) and that the use of white dwarfs to calibrate UV spectr ophotometry is valid.