CDROM/AJ/V110/P2131 M/L for Draco and UMi. I. (Armandroff+ 1995) ================================================================================ The Mass-To-Light Ratios of the Draco and Ursa Minor Dwarf Spheroidal Galaxies. I. Radial Velocities From Multifiber Spectroscopy Taft E. Armandroff, Edward W. Olszewski, & Carlton Pryor <1995, AJ, 110, 2131> =1995AJ....110.2131A ================================================================================ 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. Description: The data tables supplied by the author are not conducive to reformatting into FITS. The table descriptions below depart from the CDS standard in this regard are are meant for guidance in the overall layout of the data. Tables 2-5 contain records in two formats: a "header" record for each star giving the name, coordinates, and radial velocity data; and, following the header record, a sequence of data records with the date and velocity for measurement of that star. File Summary: -------------------------------------------------------------------------------- File Name Lrecl Records Explanations -------------------------------------------------------------------------------- table2.dat 78 406 Data for UMi stars table2.not 75 38 Notes for Table 2 table3.dat 78 327 Data for Draco stars table3.not 75 18 Notes for Table 3 table4.dat 78 132 Data for UMi non-member stars table4.not 75 6 Notes for Table 4 table5.dat 78 160 Data for Draco non-member stars table5.not 75 3 Notes for Table 5 -------------------------------------------------------------------------------- Byte-by-byte Description of files: table2.dat table3.dat table4.dat table5.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- -- Header Record -- 1- 8 A8 --- Name Primary star name 9-11 I3 --- Num Number of velocities following header 12-14 I3 h RAh Right ascension, 1950 15-17 I3 min RAm R.A. 18-23 F6.2 s RAs R.A. 24 A1 --- DE- Declination sign, always blank 25-26 I2 deg DEd Declination, 1950 27-29 I3 arcmin DEm Dec. 30-34 F5.1 arcsec DEs Dec. 35-42 F8.2 km/s Average radial velocity 43-47 F5.2 km/s e_ Uncertainty in 48-54 F7.1 --- Chi2 []? Chi-square of scatter about 55-62 E8.2 --- Prob *[]? Probability of larger Chi2 63-64 2X --- --- Blank 65-76 A12 --- Other Other names for the star 77 1X --- --- Blank 78 A1 --- Note Note number in corresponding notes file -- Data Records -- 1-10 D10.2 --- JD Julian date of the velocity 11-18 F8.1 km/s Vel Measured radial velocity 19-22 F4.1 km/s e_Vel Uncertainty in Vel 23-28 F6.2 --- R_Vel R value for the velocity 29 1X --- --- Blank 30 A1 --- Src *[ MH] Source of the velocity -------------------------------------------------------------------------------- Notes for files: table2.dat table3.dat table4.dat table5.dat -------------------------------------------------------------------------------- Prob: The probability of obtaining a chi-square as large or larger than is observed if the star has a constant radial velocity. Src: The source of the velocity, where a blank indicates a velocity measured with Hydra and reported in this paper, an M indicates an MMT echelle velocity from Olszewski et al. (1995, AJ, 110, 2120), and an H indicates a velocity from Hargreaves et al. (1994, MNRAS, 271, 693). -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.not table3.not table4.not table5.not -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1-75 A75 --- Text Text of the note -------------------------------------------------------------------------------- ================================================================================ (End) Lee Brotzman [ADS] 03-Nov-1995