Membership of 23 stars towards the bulge globular clusters NGC 6528 and NGC 6553

Low resolution spectra of 23 stars towards the bulge globular clusters NGC 6528 and NGC 6553 are analysed. Radial velocities and atmospheric parameter s are derived in order to check their membership in the clusters. Effective temperatures were obtained from photometric data for stars with T-eff > 38 00 K, whereas for cooler stars, they were derived from equivalent widths of TiO bands. Calibrations of W(TiO) as a function of stellar parameters base d on a grid of synthetic spectra are presented. Metallicities were derived from a comparison of the observed spectra to a grid of synthetic spectra. T he sample comprises evolutionary stages from the Red Giant Branch to the Ho rizontal Branch, with parameters in the range 3200 less than or equal to T- eff less than or equal to 5000 K and -0.5 less than or equal to log g less than or equal to 2.4. The mean metallicities obtained for NGC 6528 and NGC 6553 are [Fe/H] approximate to -0.5 and 0.7, in both cases with [Mg/Fe] = 0.3; assuming the same overabundance for the alpha elements O, Mg, Si, S, C a and Ti, this gives [Z=Z.] = -0.25 and -0.45. Membership verification by m eans of low resolution spectra is a crucial step in preparing targets for h igh resolution spectroscopy with 8 m class telescopes.