Relative ages of inner-halo globular clusters

Abstract

We present preliminary results from our on-going survey of Galactic globular clusters relative ages. The investigation is based on V,I images obtained at the ESO and La Palma telescopes, which make up the largest homogenous photometric catalog to date. A second, independent sample of globulars observed in the B, V bands provides an independent check of the results based on the groundbased data. Age-dependent morphological parameters are measured on the CMDs and are compared with two sets of independent models. We find that the so-called ``vertical'' and ``horizontal'' methods give compatible results when the groundbased dataset is used, and that in both cases the observed trends are well reproduced by the isochrones. The interpretation of the HST data trends are more controversial, due to both a stronger dependence on metallicity, and to the discrepancies in the theoretical loci. Our data clearly show that (a) no age dispersion can be revealed for the bulk of the GGCs at the ~1 Gyr level; (b) no age-metallicity relation is found, although the age dispersion is somwhat larger for intermediate and higher metallicity clusters; and (c) there is no clear trend with the galactocentric distance, out to the present limits of our survey (R(GC) < 22 Kpc).