Evidence for an age spread among the Galactic globular clusters

Abstract

The ages of the Galactic globular clusters are studied, based on a new interpretation of the observed Delta(V) and Fe/H abundance ratio values in terms of a parameterized model. The derived ages are in excellent agreement with those derived from isochrone fitting. Evidence is presented for an age spread of 5 Gyr, suggesting a prolonged epoch of globular cluster formation. It is found that younger clusters have high metallicity. The results suggest that the variations in age describe the observed variation in horizontal-branch morphology in Galactic clusters at a given metallicity.