THE ASTRONOMICAL JOURNAL    VOLUME 110, NUMBER 5, PAGE 2131       NOVEMBER 1995

     THE MASS-TO-LIGHT RATIOS OF THE DRACO AND URSA MINOR DWARF SPHEROIDAL
          GALAXIES. I. RADIAL VELOCITIES FROM MULTIFIBER SPECTROSCOPY

                              TAFT E. ARMANDROFF

   National Optical Astronomy Observatories, Kitt Peak National Observatory,
                     P.O. Box 26732, Tucson, Arizona 85726
                     Electronic mail: tarmandroff@noao.edu

                              EDWARD W. OLSZEWSKI

     Steward Observatory, The University of Arizona, Tucson, Arizona 85721
                  Electronic mail: eolszewski@as.arizona.edu

                                 CARLTON PRYOR

     Department of Physics and Astronomy, Rutgers, The State University of
          New Jersey, P.O. Box 849, Piscataway, New Jersey 08855-0849
                  Electronic mail: pryor@physics.rutgers.edu

                                   ABSTRACT

    We have measured 206 radial velocities for 94 probable members in the
    Ursa Minor dwarf spheroidal galaxy and 167 velocities for 91 probable
    members in the Draco dwarf spheroidal galaxy.  These velocities were
    obtained using the KPNO 4 m telescope with the Hydra multifiber
    positioner and bench spectrograph in 1992, 1993, and 1994.  Both
    simulations and repeated measurements show that the median uncertainty
    in these velocities is 4.0 km/s.  Our velocities are compared with the
    other major datasets for Draco and Ursa Minor.  Aside from a small
    zero-point difference, there is excellent agreement between the Hydra
    velocities and the Olszewski et al. MMT echelle velocities.  Comparison
    with the Hargreaves et al. Ursa Minor velocities reveals
    inconsistencies which we ascribe to underestimated errors in the
    Hargreaves et al. data.  After correcting for zero-point differences,
    we combine the three major sets of velocities.  Our spectra recovered
    all of the known Carbon (C) stars in Draco and Ursa Minor and revealed
    one new C star in Draco and two in Ursa Minor.  In addition, one star
    whose velocity is consistent with membership in Ursa Minor has a deep
    and wide HBeta absorption line in its spectrum.  An initial discussion
    of the kinematics of the two galaxies is presented.  The systemic
    velocities of Draco and Ursa Minor are -293.3 +/- 1.0 and -274 +/- 1.0
    km/s, respectively.  Ursa Minor shows apparent rotation about a
    position angle of 75 deg with an amplitude of about 3 km/s; the
    morphological major axis is 53 +/- 5 deg.  No such rotation is found in
    Draco.  We find a velocity dispersion of 10.4 +/- 0.9 km/s for Ursa
    Minor including all stars and 8.8 +/- 0.8 km/s excluding the star with
    the most extreme velocity.  In Draco we find 10.7 +/- 0.9 km/s
    including all stars and 8.5 +/- 0.7 km/s excluding the three stars with
    the most extreme velocities.  These dispersions are consistent with the
    dispersions measured in the other two studies and confirm that Draco
    and Ursa Minor have the largest mass-to-light ratios of any of the
    dwarf spheroidals.