NEW-AGE INDICATORS FOR OLD STELLAR POPULATIONS

We report on new age indicators in the integrated light of old stellar populations. Spectral indices defined by Rose in the 3800-4500 Angstr om region and two broader indices, H delta(A) and H gamma(A), have bee n measured in a spectral library of about 500 stars. The behavior of t hese indices with temperature, gravity, and [Fe/H] was modeled with po lynomials, and they were included in the population models of Worthey (1994). All definitions of H delta and H gamma are sensitive to popula tion age. One index in particular, H gamma(HR), shows a striking abili ty to separate the effects of age and metal abundance in integrated li ght.