Galactic globular clusters with extremely low metallicities

An observational program has been initiated for determining chemical abundances of red giants belonging to galactic globular clusters, whose characteristics (morphology of the horizontal branch, integrated spectral type, ultraviolet excess, etc.) suggest extremely low metallicities. In this study we present some preliminary results obtained at Cerro Tololo Inter-American Observatory from Washington photometry of 165 red giants belonging to 15 globular clusters. The metallicities have been determined using a new empirical calibration recently established by Geisler, Clariá and Minniti (1990), which accounts for the effect of decreasing abundance sensitivity of Δ(C-M) with decreasing temperature. The mean [Fe/H] values obtained for 10 of the 15 clusters range between -2.0 and -3.0. Although preliminary, these values considerably extend the metallicity distribution of the galactic globular cluster system towards values close to -3.0, thus favoring the secondary formation theory of galactic globular clusters.Asociación Argentina de Astronomí