The Carina Project. I. Bright Variable Stars

We present new BV time series data of the Carina dwarf spheroidal galaxy.Current data cover an area of about 0.3 square degrees around the center of thegalaxy and allowed us to identify 92 variables. Among them 75 are RR Lyraestars, 15 are "bona fide" Anomalous Cepheids, one might be a Galactic field RRLyrae, and one is located along the Carina Red Giant Branch. Expanding upon theseminal photographic investigation by Saha, Monet & Seitzer (1986) we supplyfor the first time accurate estimates of their pulsation parameters (periods,amplitudes, mean magnitude and colors) on the basis of CCD photometry.Approximately 50% of both RR Lyrae and Anomalous Cepheids are newidentifications. Among the RR Lyrae sample 6 objects are new candidatedouble-mode variables. On the basis of their pulsation properties we estimatedthat two variables (V152, V182) are about 50% more massive than typical RRLyrae stars, while the bulk of the Anomalous Cepheids are roughly a factor oftwo more massive than fundamental mode RR Lyrae stars. This finding supportsthe evidence that these objects are intermediate-mass stars during central Heburning phases. The data for Carina, together with data available in theliterature, strongly support the conclusion that dSph galaxies can barely beclassified into the classical Oosterhoff dichotomy. The mean period offundamental mode RR Lyrae in Carina resembles that found for Oosterhoff type IIclusters, whereas the ratio between first overtones and total number of RRLyrae is quite similar to that found in Oosterhoff type I clusters.