OGLE catalogue of variable stars in the Sculptor dwarf spheroidal Galaxy.
KALUZNY J., KUBIAK M., SZYMANSKI M., UDALSKI A., KRZEMINSKI W. and MATEO M.
Abstract (from CDS):
The central area of the Sculptor dwarf galaxy was surveyed for variable stars as a side-program of the OGLE project. Light curves in the V band were obtained for 226 RR Lyr stars and for 3 anomalous cepheids. One previously unknown anomalous cepheid was identified. We also discovered two variables located at the tip of the red giant branch of Sculptor. Out of 226 RR Lyr variables 134 were classified as RRab, 89 as RRc and one as RRd. The distribution of the periods for RRab stars shows a sharp cut-off at P=0.475 day. This implies that the bulk of Sculptor RR Lyr stars has metallicity [Fe/H]≤-1.7 on the Zinn-West scale. The average V magnitudes of RRab variables are correlated with their periods. This effect is most probably caused by the spread of metallicities exhibited by the variables. Based on the average V magnitudes of RR Lyr stars the apparent distance modulus of Sculptor was determined to be (m-M)V=19.71. We present a new color-magnitude diagram of Sculptor reaching V≃21.4 and I≃20.6. The observed width of the upper part of the red giant branch indicates a range of metallicities (-2.2≤[Fe/H]≤-1.6) for the Sculptor giants. The observed distribution of stars along the horizontal branch and the average metallicity imply that age of Sculptor is similar to that of the relatively young globular clusters from the outer galactic halo. The data on RR Lyr variables in four nearby dwarf galaxies are summarized and discussed briefly.