V, I-CCD PHOTOMETRY OF METAL-RICH GLOBULAR-CLUSTERS - NGC-6528

We present CCD photometry in V and I for the metal-rich globular clust er NGC 6528. A comparison with previous photometry reveals discrepanci es of the order 0.1 to 0.2 mag in V, emphasizing the need for independ ent photometry. As found previously, the giant branch (or the asymptot ic giant branch, which cannot be distinguished) of the cluster extends to V - I = 7. Population synthesis in V - I must take these red stars into account in order to understand integrated red colours of bulge p opulations. Currently available theoretical isochrones do not reproduc e the shape of the RGB/AGB. The derivation of reliable values for redd ening, distance and metallicity of NGC 6528 is hampered by uncertainti es in the extrapolation to high metallicity, which dominate the absolu te error rather than the photometric uncertainty does. Together with o ther properties (old age derived from HST data, high radial velocity), this object is more likely a member of the bulge than of the disk pop ulation.(1).