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Session 3 - Clusters.
Display session, Monday, June 10
Tripp Commons,
We present V vs. V-I color-magnitude diagrams (CMDs) of the nearby Galactic globular clusters M92, M3, M13, and M5, and for the outer halo clusters Palomar 4 and NGC 2419. The nearby clusters span a range in metallicity and provide a set of CMD fiducials for comparing with the distant clusters. The primary goal is to measure relative cluster ages with high precision. The outer halo CMDs will come both from ground-based data, as is presented here, and later from HST observations made in the same bandpasses. Two of the fiducial clusters, M3 and M13 are a "second parameter" pair, with similiar metallicities but different horizontal-branch morphologies. To test whether age is the cause, we use the /Delta V and color-difference (VandenBerg et al. 1990) methods to calculate age differences. Our preliminary result is that the two clusters have similar ages at the level of 1 Gyr. The observations are also compared to the theoretical isochrones of Vandenberg (1996) as a test of the color-transformations in the I-band.
