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Session 107 - Open Clusters.
Display session, Thursday, January 18
North Banquet Hall, Convention Center
We present a CCD photometric survey of two relatively unstudied open clusters, IC 361 and NGC 6802, on the BVRI system. Color-magnitude diagrams of both clusters reveal fairly populous red giant clumps and well-defined main sequences, extending about 4 to 5 magnitudes below the main sequence turnoff to V\simeq21. Comparison with evolutionary models allows us to estimate cluster properties such as metallicity, reddening, age, and distance. Using VandenBerg's (1985) theoretical isochrones, we find a best fit to the color-magnitude diagram sequences for IC 361 with parameters [Fe/H]=-0.23, E(B-V)=0.66, true distance modulus (m-M)=11.98, and an age of 1.25 - 1.5 Gyr. Likewise, for NGC 6802, we find a best fit with [Fe/H]=-0.45, true distance modulus (m-M)=10.78, and age of 1.0 Gyr. The reddening for NGC 6802 is calculated to be E(B-V)=0.94, but the width of the main sequence relative to expected observational errors suggests the influence of differential reddening to the cluster. Our revised ages for these clusters make them attractive targets for in-depth studies of both stellar evolution and the structure and chemical evolution of the Galactic disk.
Program listing for Thursday