VARIABLE-STARS IN THE SEXTANS DWARF SPHEROIDAL GALAXY

We describe a survey for variable stars in the Sextans dwarf spheroidal (dSph) galaxy based on the analysis of 113 B and 48 V CCD images of four fields covering a total area of 18'x18'. We have identified 44 variables: 36 RR Lyr star, 6 anomalous Cepheids, one long-period red variable, all probable members of Sextans, and one foreground contact binary. We have used the pulsating stars to derive a true distance modulus of 19.67+/-0.15 for Sextans (or D=86+/-6 kpc), where the error is primarily due to uncertainties in the luminosity-metallicity relation for RR Lyr stars. Based on our new data we conclude that [Fe/H](Sex)=1.6+/-0.2, somewhat higher than the value from Suntzeff er al. [ApJ, 418, 208 (1993)] obtained from the analysis of fiber spectroscopy of the near-IR Calcium triplet. We present a new deep color-magnitude diagram for Sextans which reveals the presence of a metal-poor population containing stars as young as 2-4 Gyr, consistent with the presence of anomalous Cepheids in the galaxy. This young population may represent as much as 25% of the total stellar content of Sextans. We find a surprisingly strong correlation between the frequency of anomalous Cepheids in dSph galaxies and galaxian luminosity and speculate on the possible origin of this strange effect. The RR Lyr stars in Sextans do not exhibit the Oosterhoff dichotomy observed in globular clusters and in the Galactic halo field. (C) 1995 American Astronomical Society.