AAS 199th meeting, Washington, DC, January 2002
Session 56. Globular Clusters
Display, Tuesday, January 8, 2002, 9:20am-6:30pm, Exhibit Hall

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[56.14] Variable Stars in the Fields of the Globular Clusters M10 and M12

K. von Braun, M. Mateo, K. Chiboucas, A. Athey (University of Michigan), D. Hurley-Keller (Case Western Reserve University)

We present the photometry results of our extensive monitoring study of the Globular Clusters (GCs) M10 and M12. These two clusters are part of our survey of 11 Galactic GCs in which we search for eclipsing binary (EB) stars around the main-sequence turnoff by means of photometrically detecting brightness variations.

The straightforward, though data-intensive, task of simply detecting EBs in GCs and confirming their cluster membership increases the presently low number of known EB systems in GCs. A statistical evaluation of this number may shed light on the influence of binaries in the dynamical evolution of GCs. Ultimately, the simultaneous photometric and spectroscopic analysis of these systems may be used to directly determine distances to the clusters and to calculate turnoff masses for GC stars. The distance determination, free of intermediate steps, can provide distances out to tens of kpc and may be used to calibrate other, indirect distance determination methods. Values for main-sequence masses of GC stars provide a fundamental, low metallicity check of stellar models. In order to obtain zero-age mass-estimates for the components in a binary system, one needs to take into account the mass transfer history between the two stars, which demonstrates the value of detecting unevolved, detached binaries where no mass transfer has taken place.

Our observing strategy consists of repeated observations of the entire cluster field. The first results of this approach are high-quality, deep color-magnitude diagrams (CMDs) of the clusters. In this presentation we show the phased lightcurves of all variable star candidates in the fields of the two cluster along with their locations in the respective CMD and positions in the clusters. In addition, we provide our estimates for cluster membership of the binary systems based on their CMD locations and the Rucinski method for calculating absolute magnitudes of contact binaries.

The author(s) of this abstract have provided an email address for comments about the abstract: kaspar@astro.lsa.umich.edu

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