No abstract

We have observed (with vby Ðlters) a Ðeld north of the core of the most massive globular cluster in our galaxy, u Centauri. We have found a correlation of age and metallicity in a region that avoids the dense core and the inhomogeneous foreground dust emission shown by IRAS. Our observations show that the comparatively metal-rich stars (as deÐned by the b[y and colors) are younger than the m 1 metal-poor stars by at least 3 Gyr. This correlation of metallicity with age suggests that u Cen has enriched itself over a timescale of about 3 Gyr, and possibly longer. It is remarkable that ejecta from stellar winds combined with supernovae of Type II failed to disperse the clusterÏs interstellar matter at an earlier epoch but were captured by the cluster instead. Star formation would have ceased as Type Ia supernovae dispersed the remaining interstellar matter. This work and other recent evidence suggests that u Cen could have been part of a small satellite galaxy in which all the activity occurred before it was captured by the Milky Way.