Guinan, DeWarf, Maloney and P. A. Maurone (Physics Dept.), with D.
H. Bradstreet (Eastern Coll.) and Y. W. Kang (Sejong U., Seoul, Kor.),
are actively researching eclipsing binaries in the Magellanic Clouds.
These systems are important laboratories for studying stellar structure,
evolution, and mass loss for stars with reduced metallicity. They have
obtained IUE SWP (1150-2000Å) spectra of a dozen hot O/B
eclipsing systems in the LMC and SMC that have well determined light and
radial velocity curves. During Fall 1996 HST FOS and GHRS observations
are scheduled for ten of these systems. The chief purpose of the UV spectrophotometry is to determine temperatures and reddenings for
these stars. Since these stars radiate most of their energy in the UV, the character of the UV continuum and the presence of highly
ionized elements are sensitive measures of stellar temperatures. The
UV data have been combined with the UBV (or uvby)
photometry and fit with the most recent version (ATLAS13) of Kurucz
model atmospheres at metal abundances appropriate for the LMC or SMC.
Ground-based light and radial velocity curves are obtained in
collaboration with W. Tobin and J. Pritchard (U. Canterbury,
Christchurch, NZ), V. Niemela (La Plata, ARG), A. Giménez
(INTA/LAEFF, SP), and J.-V. Claussen (Denmark) and provide masses and
radii. These data, when combined with the UV spectrophotometry
give accurate stellar luminosities. This leads to a first direct
Mass-Luminosity relationship, using directly measured masses and
luminosities, for stars outside the Milky Way, and extends the parameter
space in stellar interior models to chemical compositions different from
the Milky Way. These eclipsing binaries can also serve as first class
standard candles. Because the uncertainty in the ground-based
determination of their temperatures presently contributes the greatest
uncertainty in their computed distances, the more precise temperatures
obtained from UV spectra, combined with the well determined
stellar radii, will allow us to compute the distance moduli to these
stars to within 
mag. This research is supported by NASA
grants NAG5-2160 and NSF grant AST-9315365.