WFPC2 OBSERVATIONS OF THE CARINA DWARF SPHEROIDAL GALAXY

We present our analysis of Hubble Space Telescope Wide Field Planetary Camera 2 observations in F555W (similar to V) and F814W (similar to I ) of the Carina dwarf spheroidal galaxy. The resulting V vs V-I color- magnitude diagrams reach V approximate to 27.1 mag. The reddening of C arina is estimated to be E(V-I) = 0.08+/-0.02 mag. A new estimate of t he distance modulus of Carina, (m-M)(0) = 19.87+/-0.11 mag, has been d erived primarily from existing photometry in the literature. The appar ent distance moduli in V and I were determined to be (m - M)(V) = 20.0 5+/-0.11 mag and (m - M)(I) = 19.98+/-0.12 mag, respectively. These de terminations assumed that Carina has a metallicity of [Fe/H]= -1.9+/-0 .2 dex. This space-based observation, when combined with previous grou nd-based observations, is consistent with (but does not necessarily pr ove the following star formation scenario, The Carina dwarf spheroidal galaxy formed its old stellar population in a short burst (less than or similar to 3 Gyr) at about the same time the Milky Way formed its g lobular clusters. The dominant burst of intermediate-age star formatio n then began in the central region of the galaxy where stars formed fo r several billion years before the process of star formation became ef ficient enough in the outer regions of the galaxy to allow for the for mation of large numbers of stars. There has been negligible star forma tion during the last few billion years, This observation provides evid ence that at least some dwarf galaxies can have complex global star fo rmation histories with local variations of the rate of star formation as a function of time and position within the galaxy. (C) 1997 America n Astronomical Society.