DWARF CEPHEIDS IN THE CARINA DWARF SPHEROIDAL GALAXY

We have discovered 20 dwarf Cepheids (DCs) in the Carina dwarf spheroi dal galaxy from an analysis of individual CCD images obtained for a de ep photometric study of the system. These short-period pulsating varia ble stars are by far the most distant (similar to 100 kpc) and faintes t (V similar to 23.0) DCs known. The Carina DCs obey a well-defined pe riod-luminosity relation, allowing us to readily distinguish between o vertone and fundamental pulsators in nearly every case. Unlike RR Lyra e stars, the pulsation mode turns out to be uncorrelated with light-cu rve shape, and the overtone pulsators do not tend toward shorter perio ds compared with the fundamental pulsators. Using the period-luminosit y relations from Nemec, Nemec, & Lutz and McNamara, we derive (m - M)( 0) = 20.06 +/- 0.12, for E(B - V) = 0.025 and [Fe/H] = -2.0, in good a greement with recent, independent estimates of the distance/reddening of Carina. The error reflects the uncertainties in the DC distance sca le, and in the metallicity and reddening of Carina. The frequency of D Cs among upper-main-sequence stars in Carina is approximately 3%. The ratio of dwarf Cepheids to RR Lyrae stars in Carina is 0.13 +/- 0.10, though this result is highly sensitive to the star formation history o f Carina and the evolution of the horizontal branch. We discuss how DC s may be useful to search effectively for substructure in the Galactic halo out to Galactocentric distances of less than or similar to 100 k pc.