Stellar Abundances in Giant Stars in the Metal - Rich Globular Cluster NGC 6528

We present the first results of a detailed abundance analysis, based on VLT observations, of giant stars in the very metal-rich globular cluster NGC 6528. We will, we hope, be able to tie the horizontal branch abundances (see e.g. Carretta et al. 2001) to those of the more luminous giants (see CMDs). For the very similar cluster NGC 6553 studies of different types of stars have yielded very disparate results. Our first analysis of three of our stars seem to indicate that indeed the different sorts of stars do show similar abundances if one homogeneous set of models and parameters are being used. Introduction NGC 6528 is perhaps the most metal-rich globular cluster known and as such serves as an invaluable template for calibrating and understanding metal-rich stellar populations in extra-galactic bulges and disks, as well as serving as a template in studies of our own Galactic Bulge. So far, observations of this cluster have been, however, severely hampered by it being superimposed on and physically close to the Galactic Bulge itself. But now, using our second epoch HST/WFPC2 observations, we were able to provide a disentangling of Bulge and cluster and could therefore propose a detailed abundance analysis of bona fide cluster members. These would determine the metallicity of the cluster (very much debated, values between -0.6 to +0.2 dex are found in the literature), as well as the α-enhancement in the cluster, thus providing vital clues to both the formation of globular clusters as well as time-scales for the formation of the Galaxy. The α-enhancement is also important to know when deriving an age from fitting of the main-sequence turn-off in the colour-magnitude diagram as α-enhancement changes the isochrones such that the age for a given metallicity gets younger (see Salasnich et al., 2000, and for an application to metal-rich clusters Feltzing & Johnson, 2002) Stellar sample The stars for the UVES observations were selected as being cluster members based on the individual stellar proper motions for stars in NGC 6528 and the surrounding field (Feltzing & Johnson, 2002). We selected both stars on the horizontal branch as well as on the upper red giant branch. Stellar abundances The measured equivalent widths are analysed using a standard LTE abundance calculation with MARCS model atmospheres (Gustafsson et al., 1975, and subsequent updates). Line data are from Bensby et al. (2002 in prep.) in particular Fe, Si and, Ti have laboratory log gf while Ca and Cr have