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Session 45 - Eclipsing Binaries.
Display session, Thursday, January 08
The fundamental parameters of O-type stars are important tests of the theoretical predictions of massive stars. The most direct observational means of determining these parameters is through the study of binaries. In order for the mass of the component stars in a double-lined spectroscopic binary to be determined, some estimate of the inclination must be found. This emphasizes the importance of double-lined systems that also show light variations due to their orbital inclination (eclipses, ellipsoidal variations). A member of NGC 6231, HD 152248 was identified by Struve as a double-lined system in 1944. The spectroscopic orbit has been well studied since that time by various groups, the last being Stickland et al. (1996). However its eclipsing nature was only discovered by Mayer, Lorentz, amp; Drechsel in 1992. The system shows unequal minima and unequally spaced eclipses. The shapes of the eclipses and tidally-related ellipsoidal variation in the observed light curve are key clues to the stellar radii and orbital inclination, and we present a preliminary light curve solution. We also present our determinations of individual spectral classifications (from the IUE spectra) and projected rotational velocities. We discuss the constraints on inclination and system masses based on cluster distance modulus, presumed synchronous rotation, and on consistency with masses derived from evolutionary tracks.
Program listing for Thursday