AGE AND METALLICITY EFFECTS IN SINGLE STELLAR POPULATIONS - APPLICATION TO M31 CLUSTERS

We have recently calculated (Boges et al. 1995) integrated metallicity indices for single stellar populations (SSP). Effects of age, metalli city and abundances were taken into account. In particular, the explic it dependence of the indices Mg-2 and NaD respectively on the ratios [ Mg/Fe] and [Na/Fe] was included in the calibration. We report in this work an application of those models to a sample of 12 globular cluster s in M 31. A fitting procedure was used to obtain age, metallicity and the [Mg/Fe] ratio for each object, which best reproduce the data. The mean age of the sample is 15+/-2.8 Gyr and the mean [Mg/Fe] ratio is 0.35+/-0.10. These values and the derived metallicity spread are compa rable to those found in galactic counterparts.