SIMBAD references

We present a new technique for the determination of age and metallicity in composite stellar populations using Strömgren filters. Using principal component (PC) analysis on multicolor models, we isolate the range of values necessary to uniquely determine age and metallicity effects. The technique presented here can only be applied to old (τ>3 Gyr) stellar systems composed of simple stellar populations, such as globular clusters and elliptical galaxies. Calibration using new photometry of 40 globular clusters with spectroscopic [Fe/H] values and main-sequence-fitted ages links the PC values to the Strömgren colors, for an accuracy of 0.2 dex in metallicity and 0.5 Gyr in age.Subject headings: