Bursts of star formation in the Carina dwarf spheroidal galaxy
Session 51 -- Dwarf Galaxies
Display presentation, Tuesday, 10, 1995, 9:20am - 6:30pm

[51.06] Bursts of star formation in the Carina dwarf spheroidal galaxy

T.A. Smecker-Hane, P.B. Stetson, J.E. Hesser (NRC/HIA/DAO)

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We present evidence for bursts in the star-formation history of the Carina dwarf spheroidal galaxy, a nearby satellite of the Galaxy. Our long range goal is to determine the star-formation history and chemical evolution of dwarf galaxies. Two questions we seek to answer are whether bursts of star formation are common in dwarfs, and how important are massive dark-matter halos and galactic winds in shaping their evolution. We present a deep color-magnitude diagram of Carina obtained with the CTIO 4m telescope in $B$ and $R$ filters that reaches to $V=24.5$. At least four distinct main-sequence turnoffs are apparent. Using the Revised Yale Isochrones (Green, et al. 1987) as a comparison, we find stellar populations with approximate ages of 4 Gyr, 5-8 Gyr, and 12-15 Gyr. Also, we find a sequence which may represent very young stars (2 Gyr) or a population of blue stragglers. Notable is the relative absence of stars with ages of $\sim 8-12$ Gyr, which suggests a hiatus in star formation lasting for several Gyr. Clearly, this small galaxy on the periphery of the Milky Way ($R_{GC} = 105$ kpc) has had a much more complex evolution than globular clusters at comparable $R_{GC}$. Comparing the observed color-magnitude diagram to new theoretical models and comparison with globular clusters will allow us to better estimate the ages of Carina stars and infer its star-formation history.