Beatriz Barbuy

Oxygen overabundances in metal-poor stars were first derived by Conti etal. (1967, ApJ, 148, 105) and Sneden etal. (1979, ApJ, 234, 964), who give a value [O/Fe]= +0.6 for the most metal-poor stars. Controversies on the absolute value of the oxygen overabundance were started with the works by Gratton & Ortolani (1986, A&A, 169, 201) and Barbuy (1988, A&A, 191, 121), who claimed that the overabundance should be [O/Fe] s 0.4, and constant in the halo.

We have calculated TiO and total spectra, in steps of 0.02 A, using the code by Barbuy (1989, Ap&sSS, 157, 111) in the red and near-infrared regions. The employed model atmospheres are interpolated in the grids of models by Bell et al. (1976, A&AS, 23, 37) and by B. Gustafsson (p.c.). The photospheric parameters used are: Te£ = 4000, 4500, 5000, 5500 K; log g = 0.0, 1.0, 2.0, 3.0, 4.0, 4.5, 5.0; and [M/H] = —3.0, —2.0, —1.0, 0.0, +0.5 dex.

We have applied synthetic spectra calculations to low resolution spectra of metal-rich stars observed by Pickles (1985, Ap]JS, 59, 33), for two bulge stars (Castro et al. 1992, TAU Symposium 153) and one star in the bulge globular cluster NGC 6553 (Barbuy etal. 1992, A&A, 259, 607), in order to derive their metallicities. The observations were obtained by A. Pickles at the 3.6-m, by T. Richtler at the 1.5-m and by ourselves at the 3.6-m at ESO.