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Session 82 - Globular Clusters.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center

[82.09] Spectroscopic Masses of Binary Stars in the Globular Cluster M 71

M. Mateo (U. Mich.), L. Yan (Caltech/ESO)

We have obtained time-resolved spectroscopy of four of the eclipsing binaries in the nearby globular cluster M 71. Partial spectroscopic coverage was obtained for a fifth cluster binary that could not be observed simultaneously with the other systems. These data were obtained in 1995 Sept using the multi-slit capability of the RC Spectrograph on the 4m telescope at Kitt Peak. Individual velocities accurate to 7-10 km s^-1\ have been derived from these spectra of the binaries. We also were able to obtain 2-3 observations at each quadrature of each variable; thus, the binary velocity amplitudes should be determined to 5-7 km s^-1. The velocity measurements have been phased using the high-quality light curves of Yan and Mateo (1994, AJ, 108, 1810) supplemented with additional photometry obtained close to the spectroscopic run. We will present the velocity curves of these binaries, and derive precise mass estimates of the individual stars. These results constitute the first direct determinations of the masses of any main sequence stars in a globular cluster. We shall critically compare our mass estimates with that expected from stellar evolutionary models that fit the photometric properties of the stars in M 71 very well. Our spectroscopic observations also directly constrain the distance of M 71 completely independently of any other distance scale.

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