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

5.7 NGC 6822

The dwarf irregular galaxy NGC 6822 has a conspicuous population of recently formed and forming stars [see references in Hodge et al. (70) and Azzopardi et al. (11). Color-magnitude diagrams (63, 74, 81), neutral hydrogen measurements (50), HII region studies (70, 75, 82, 99), and the existence of Wolf-Rayet stars (7, 11, 129) all have contributed to our knowledge of the young population of NGC 6822. Most results on the abundances in NGC 6822 suggest that it is just a little more metal poor than the LMC, with Z = 0.0045, a value that conforms to its low Wolf-Rayet star population (11).

It is less clear just what kind of old population this galaxy has. There is at least an intermediate population, as shown by the presence of fairly luminous giants, but little has been deduced about the relative numbers of intermediate-age stars or the numbers of very old stars. The oldest clusters (68) suggest that the initial burst of star formation, if there was one, was relatively weak; at the least, it failed to produce more than one or two rather small globularlike clusters.