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Session 71 - Globular Clusters.
Display session, Wednesday, January 15
Metropolitan Ballroom,

[71.12] Eclipsing Binary Stars in Globular Clusters

K. von Braun, M. Mateo (U. Michigan), L. Yan (ESO)

We present the results of our photometric monitoring project in V and I of the Galactic globular clusters M12, M15, NGC3201, and NGC6752, carried out at the Michigan-Dartmouth-MIT and Las-Campanas-Observatories over the past two years.

Our aim is to identify candidates for eclipsing binary systems in these clusters for which we will then perform subsequent spectroscopic observations. The combination of the photometric and spectroscopic data can provide estimates of the masses of the individual binary components as well as the distance to the cluster.

The distance estimate, which is independent of other distance scales to globular clusters, may be used to calibrate indirect distance measurement methods. In particular, the results will help establish the zero point of the RR Lyrae distance scale, and could ultimately help determine the slope of the RR Lyrae luminosity-[Fe/H] relation.

The values of the masses will, in the case of an evolved binary system (with mass transfer and/or loss), provide a lower limit to the cluster's turnoff mass at its present age. For a non-evolved binary systems, we will be able to get a direct estimate of the turnoff mass. These values will be independent of cluster metallicity, interstellar reddening, as well as stellar evolution and cosmological models.

We present the updated results of our search for binaries in our target clusters, as well as deep photometry color-magnitude-diagrams of M12 and NGC6752, derived from co-adding the images of the clusters. In addition, we report spectroscopic results for the cluster M71 in the form of radial velocity curves of three short-period binaries in the cluster. These represent the first main-sequence binary radial velocity curves for any globular cluster. We confirm their membership in the cluster and discuss our preliminary estimates of the binary components' masses, as well as what they mean regarding the cluster age.

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