Uncertainties of Synthetic Integrated Colors as Age Indicators

We investigate the uncertainties in the synthetic integrated colors of simplestellar populations. Three types of uncertainties are from the stellar models,the population synthesis techniques, and from the spectral libraries. Despitesome skepticism, synthetic colors appear to be reliable age indicators whenused for select age ranges. Rest-frame optical colors are good age indicatorsat ages 2 -- 7Gyr. At ages sufficiently large to produce hot HB stars, theUV-to-optical colors provide an alternative means for measuring ages. This UVtechnique may break the age-metallicity degeneracy because it separates oldpopulations from young ones even in the lack of metallicity information. Onecan use such techniques on extragalactic globular clusters and perhaps even forhigh redshift galaxies that are passively evolving to study galaxy evolutionhistory.Comment: 38 pages, 21 figures, LaTex, 2003, ApJ, 582 (Jan 1), in pres