Analysis of integrated spectra of red star clusters in the Magellanic Clouds

Abstract

SIT digital spectra of the integrated light of 16 ''red'' star clusters in the Magellanic Clouds exhibit a wide variation of hydrogen line strength from cluster to cluster. In a plot of Balmer line against Ca K line equivalent width, almost all of the clusters in the sample lie apart from an empirical sequence of Galactic globular clusters. At given metallic line strength, the Cloud clusters have stronger Balmer lines. This is interpreted as indicating that few among the populous clusters in the Magellanic Clouds are as old as globular clusters. According to models of the integrated light, Balmer line strength remains sensitive to stars at the turnoff, and therefore to age, for faint turnoffs that are difficult to reach in a color-magnitude study. In the case of NGC 2209, for which both methods may be applied, good agreement is found for an age 2.1 +- 0.6 x 10/sup 9/ yr and a metallicity (Fe/H)roughly-equal-1. In the case of Kron 3, it is predicted that its turnoff, when securely known, will be fainter than V = 22. When combined with synthetic spectra for a range of age and composition, the hydrogen-metals diagnostic diagram has the potential to yield quantitative, independent more » estimates of age and metallicity with a modest investment of observing time. Integrated spectra of star clusters are a practival tool for exploring the history of chemical enrichment in galaxies too distant for the application of techniques based on single stars. « less