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 tomodel atmospheres and present initial results. Using a sample of lightlyreddened stars, we demonstrate that the Kurucz model atmospheres can produceexcellent fits to either combined low dispersion IUE and optical photometry orHST FOS spectrophotometry, as long as the following conditions are fulfilled: 1) an extended grid of Kurucz models is employed, 2) the IUE NEWSIPS data are placed on the FOS absolute flux system using theMassa & Fitzpatrick (1999) transformation, and 3) all of the model parameters and the effects of interstellar extinction aresolved for simultaneously. When these steps are taken, the temperatures, gravities, abundances andmicroturbulence velocities of lightly reddened B0-A0 V stars are determined tohigh precision. We also demonstrate that the same procedure can be used to fitthe energy distributions of stars which are reddened by any UV extinction curvewhich can be expressed by the Fitzpatrick & Massa (1990) parameterizationscheme. We present an initial set of results and verify our approach throughcomparisons with angular diameter measurements and the parameters derived foran eclipsing B star binary. We demonstrate that the metallicity derived fromthe ATLAS 9 fits to main sequence B stars is essentially the Fe abundance. Wefind that a near zero microturbulence velocity provides the best-fit to all butthe hottest or most luminous stars (where it may become a surrogate foratmospheric expansion), and that the use of white dwarfs to calibrate UVspectrophotometry is valid.Comment: 17 pages, including 2 pages of Tables and 6 pages of Figures. Astrophysical Jounral, in pres