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J.D. Hughes (Georgia Southern University), G. Wallerstein (University of Washington)
We have observed a field north of the core of the most massive globular cluster in our galaxy, \omega centauri, with vby filters. We looked for a correlation of age and metallicity in a region which avoids the dense core and the inhomogeneous foreground dust emission shown by the IRAS satellite. Our observations show that [Fe/H]= -1.4 with a 1.0 dex spread at the main-sequence turn-off. By dividing the stars into three groups with -2.2<[Fe/H] <-1.6, -1.6<[Fe/H]<-1.2, and -1.2<[Fe/H]<-0.5, we investigated the connection between age and metallicity. Plotting a color-magnitude diagram for each group with the most recent \alpha-enhanced isochrones yields an age of 14 Gyr for the most metal-poor group. The intermediate-metallicity group has a likely age of 12 Gyr, and the most metal-rich stars have an age near 10 Gyrs. This clear correlation of metallicity with age shows that \omega Cen has enriched itslef over a timescale of roughly 4 Gyr. Apparently, star formation ceased approximately 10 Gyr ago, when type Ia supernovae dispersed the remaining interstellar matter. The cluster was massive enough that the interstellar matter was not dispersed by earlier epochs of stellar winds and type II supernovae.
The author(s) of this abstract have provided an email address for comments about the abstract: joannehc@gsaix2.cc.gasou.edu