Galactic Globular Clusters as Calibrators of Synthetic Line Indices

Abstract

Models of Simple Stellar Populations (SSP) are commonly used to infer the ages and the metallicities of complex stellar systems (e.g. elliptical galaxies). In order to obtain reliable informations, these models have to becalibratedon globular clusters. In this contribution, we compare various synthetic optical colours and line indices to Galactic Globular Cluster (GGC) data. We examine different metallicity scales for GGCs, concluding that the classical Zinn (1985) scale leads to the best match between SSP models and data. The H/3 line strenghts in GGCs increase at metallicities [Fe/H] 12 Gyr) and low metallicities and are well reproduced by our models. As a consequence, composite stellar populations containing a small fraction of old and metal poor stars succeed in explaining the strong Hs lines observed in elliptical galaxies (Maraston&Thomas 1999 [22]).