Eclipsing Binaries in the Magellanic Clouds: Laboratories for Stellar Structure and Evolution

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Session 85 -- Binaries
Display presentation, Wednesday, 11, 1995, 9:20am - 6:30pm

[85.22] Eclipsing Binaries in the Magellanic Clouds: Laboratories for Stellar Structure and Evolution

D.H. Bradstreet (Eastern Coll.), L.E. DeWarf, E.F. Guinan, F.P. Maloney, \& P.A. Maurone (Villanova U.)

Eclipsing binaries in the Magellanic clouds provide important laboratories for studying stellar structure, evolution, and mass loss for star with reduced metallicity. Over the last two years, we have obtained IUE SWP (1150-2000 \AA) spectra of several hot O/B eclipsing systems in the LMC and SMC that have well determined light and radial velocity curves. The chief purpose of the UV spectrophotometry is to determine temperatures for the stars of these systems. 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. These data, when combined with values for the masses and radii obtained from ground-based light and radial velocity curves, provide accurate stellar luminosities. This leads to the first 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 IUE spectra, combined with the well determined stellar radii, will allow us to compute the distance moduli to these stars to within $\pm0.15$ mag.

In particular, we will discuss temperature determinations and the derived physical properties and distances of two well studied detached eclipsing binary systems in the LMC: HV2274 and HV5936.

This research is supported by NASA grants NAG5-2160 and NSF grant AST-9315365.

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