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We report on new age indicators in the integrated light of old stellar populations. Spectral indices defined by Rose in the 3800-4500 A region and two broader indices, HδA and HγA, have been measured in a spectral library of about 500 stars. The behavior of these indices with temperature, gravity, and [Fe/H] was modeled with polynomials, and they were included in the population models of Worthey (1994). All definitions of Hδ and Hγ are sensitive to population age. One index in particular, HγHR, shows a striking ability to separate the effects of age and metal abundance in integrated light.
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Jones et al. (1995) studied this question.
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