SPECTROPHOTOMETRIC INDEXES AND METAL CONTENT OF GALACTIC GLOBULAR-CLUSTERS

Spectrophotometric indices for 18 Galactic globular clusters, obtained from CCD observations and careful reductions, were used to determine reliable calibrations on metallicity [Fe/H]. The indices were measured in the bandpasses adopted by Burnstein et al. (1984). Adding other ob servations of Burnstein et al. (1984) we obtained our results from an homogeneous sample of indices for 26 globular clusters. Relations with indices defined by other Authors and with metallicity photometric ind ices or parameters were also computed. In each case the relations are quite satisfactory. Observational data were compared with synthetic in dices derived from Buzzoni's (1989) models and detailed discussions we re performed for Mg-2, Fe-52, and H-beta. The observational points see m to be systematically shifted with respect to the fiducial lines trac ed by the models. The scenario confirms that a certain degree of oxyge n enhancement would be necessary to obtain a better agreement between observed data and theoretical predictions. This enhancement, however, removes some of the disagreement, but not all of it. The dependence of the observed Fe-52 and H-beta indices on the metal content for differ ent HB morphologies was considered. Finally, some results were also di scussed from a statistical point of view. A principal component analys is was applied to the index sample to study the number of independent parameters necessary to reproduce the observations. The whole index se t is completely consistent with a one-parameter family.