THE ASTRONOMICAL JOURNAL    VOLUME 110, NUMBER 3, PAGE 1141      SEPTEMBER 1995

         THE OPTICAL GRAVITATIONAL LENSING EXPERIMENT: VARIABLE STARS
                  IN THE SAGITTARIUS DWARF SPHEROIDAL GALAXY

                                  MARIO MATEO

     Department of Astronomy, University of Michigan, 821 Dennison Bldg.,
                        Ann Arbor, Michigan 48109-1090
                  Electronic mail: mateo@astro.lsa.umich.edu

                    M. KUBIAK, M. SZYMANSKI, AND J. KALUZNY

   Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
   Electronic mail: mk@sirius.astrouw.edu.pl, msz@sirius.astrouw.edu.pl,
                         jka@sirius.astrouw.edu.pl

                         W. KRZEMINSKI AND A. UDALSKI

               Carnegie Observatories, Las Campanas Observatory,
                         Casilla 601, La Serena, Chile
  Electronic mail: wojtek@roses.ctio.noao.edu, udalski@sirius.astrouw.edu.pl

                                   ABSTRACT

    We present time-series CCD photometry of a field in the newly
    discovered dwarf spheroidal galaxy in Sagittarius (hereafter Sgr), and
    of a nearby control field.  These data, which consist of VI images
    obtained during the 1994 OGLE season, were used to identify and study
    variable stars in both fields.  We discovered ten variable stars in the
    Sgr field, nine of which have light curves and periods consistent with
    RR Lyr stars or anomalous Cepheids.  The control field contains four
    short-period contact eclipsing binaries, but no pulsating variables.
    The variables in the Sgr field include a bright RR Lyr star that is
    almost certainly located in front of Sgr in the galactic bulge, a
    short-period contact binary located near or within Sgr, and a
    short-period pulsating star that may either be a foreground halo RR Lyr
    star or an anomalous Cepheid within Sgr.  The seven remaining variables
    in the Sgr field are RR Lyr stars with very similar mean apparent
    magnitudes; we conclude that they are members of Sgr.  We estimate the
    total number of RR Lyr stars in Sgr to be 1930 +/- 730 if M(V,Sgr) =
    -13, or 310 +/- 120 if M(V,Sgr) = -11.  The frequency of pulsating
    variables in Sgr is consistent with earlier conclusions that the galaxy
    consists of a predominant old (age >~ 10 Gyr) population.