THE STAR-FORMATION HISTORY OF THE CARINA DWARF GALAXY

We have analyzed deep B and V photometry of the Carina dwarf spheroida l galaxy reaching below the old main-sequence turnoff to V similar to 25. Using simulated color-magnitude diagrams to model a range of star formation scenarios, we have extracted a detailed, global star formati on history. Carina experienced three significant episodes of star form ation at similar to 15, 7, and 3 Gyr. Contrary to the generic picture of galaxy evolution, however, the bulk of star formation, at least 50% , occurred during the episode 7 Gyr ago, which may have lasted as long as 2 Gyr. For unknown reasons, Carina formed only 10%-20% of its star s at an ancient epoch and then remained quiescent for more than 4 Gyr. The remainder (similar to 30%) formed relatively recently, only 3 Gyr ago. Interest in the local population of dwarf galaxies has increased lately because of their potential importance in the understanding of faint galaxy counts. We surmise that objects like Carina, which exhibi ts the most extreme episodic behavior of any of the dwarf spheroidal c ompanions to the Galaxy, are capable of contributing to the observed e xcess of blue galaxies at B similar to 24 only if the star formation o ccurred instantaneously.