THE MASS-TO-LIGHT RATIOS OF THE DRACO AND URSA-MINOR DWARF SPHEROIDALGALAXIES .1. RADIAL-VELOCITIES FROM MULTIFIBER SPECTROSCOPY

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 ob tained using the KPNO 4 m telescope with the Hydra multifiber position er and bench spectrograph in 1992, 1993, and 1994. Both simulations an d repeated measurements show that the median uncertainty in these velo cities is 4.0 km/s. Our velocities are compared with the other major d atasets for Draco and Ursa Minor. Aside from a small zero-point differ ence, there is excellent agreement between the Hydra velocities and th e Olszewski ct al. MMT echelle velocities. Comparison with the Hargrea ves et al. Ursa Minor velocities reveals inconsistencies which we ascr ibe to underestimated errors in the Hargreaves et al. data. After corr ecting 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 me mbership in Ursa Minor has a deep and wide HP absorption line in its s pectrum. An initial discussion of the kinematics of the two galaxies i s presented. The systemic velocities of Draco and Ursa Minor are -293. 3+/-1.0 and -247.4+/-1.0 km s(-1), respectively. Ursa Minor shows appa rent rotation about a position angle of 75 degrees with an amplitude o f about 3 km s(-1); the morphological major axis is 53 degrees+/-5 deg rees. No such rotation is found in Draco. We find a velocity dispersio n of 10.4+/-0.9 km s(-1) for Ursa Minor including all stars and 8.8+/- 0.8 km s(-1) excluding the star with the most extreme velocity. In Dra co we find 10.7+/-0.9 km s(-1) including all stars and 8.5+/-0.7 km s( -1) 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 mas s-to-light ratios of any of the dwarf spheroidals. (C) 1995 American A stronomical Society.