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Session 3 - Source Surveys, Galaxy Surveys, Distance Scale I.
Display session, Wednesday, January 07
We report on the progress in our study of selected detached, eclipsing binaries in the Magellanic Clouds, begun with IUE and continued with HST. The chief aims are the determination of accurate temperatures, reddenings, and chemical abundances for the component stars. Twelve systems were observed with IUE during 1993-1995, mainly with the SWPLO camera (115-200nm). During 1996/97, HST/FOS observations (in the 115-480nm range) were secured from ten of these systems. Also, HST/GHRS medium resolution spectra of two systems (HV 2274 and HV 12634) were secured in order to measure radial velocities so that stellar masses could be obtained. The UV results are being combined with radii and masses of the stars obtained from ground-based photometry and spectroscopy. This yields the first directly determined Mass-Luminosity relation for stars outside our Galaxy. Moreover, these eclipsing binaries can serve as ``standard candles'', providing direct, independent and accurate distances to the LMC and SMC. To illustrate the procedure, we present preliminary results for the LMC eclipsing binary HV 2274 (B1 IV-III + B1 IV-III; V_max = +14.2mag; P = 5.72d, e = 0.128). HV 2274 is particularly interesting because it has an eccentric orbit and shows fast apsidal motion. We have determined the physical properties of HV 2274 (masses, radii, temperatures, luminosities, chemical abundances, and internal structures of the stars) from the combined analyses of light curves taken from ground-based observations and radial velocities taken from HST/GHRS spectra. The temperatures and the metallicities of the stars are determined by modeling of IUE and HST/FOS UV-Optical spectrophotometry. Moreover, HV 2274 is providing an accurate distance determination to the LMC of m-M = +18.54\pm0.08 mag., in good agreement with other recent distance determinations to the LMC.
Program listing for Wednesday