Age and metallicity effects in omega Centauri: Stromgren photometry at the main-sequence turnoff

We have observed (with upsilon by filters) a field north of the core of the most massive globular cluster in our galaxy, omega 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 defined by the b - y and m(1) colors) are younger than the metal-poor stars by at least 3 Gyr. This correlation of metallicity with age suggests that omega 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 cluster's 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 omega Cen could have been part of a small satellite galaxy in which all the activity occurred before it was captured by the Milky Way.