Annu. Rev. Astron. Astrophys. 1989. 27: 139-59 Copyright © 1989 by Annual Reviews. All rights reserved

5.17 Carina

The Carina dwarf galaxy is a very different matter. Although there are RR Lyrae variables (107) and carbon stars (91) present, and thus a normal population (including a basic old population) is probably present, most of the galaxy's stars seem to be of intermediate age (90). The age determined from the turnoff is 7.5 ± 1.5 Gyr, and Mould & Aaronson find that the luminosity function does not permit a significant number of very old stars. Thus, Carina seems to be a unique object in the Local Group, an elliptical galaxy that did not form until after the Universe was old, but that only formed stars for a relatively short time. Figure 15 illustrates schematically its probable star formation history: a very slow start, a peak at about half the age of the Universe, and then a rapid decrease to quiescence.

Figure 15. The population history of the Carina dwarf elliptical.