LEO V: SPECTROSCOPY OF A DISTANT AND DISTURBED SATELLITE

We present a spectroscopic study of Leo V, a recently discovered satellite of the Milky Way ( MW). From stellar spectra obtained with the MMT/Hectochelle spectrograph we identify seven likely members of Leo V. Five cluster near the Leo V center ( R < 3') and have a velocity dispersion of 2.4(-1.4)(+2.4) km s(-1). The other two likely members lie near each other but far from the center (R similar to 13' similar to 700 pc) and inflate the globalvelocity dispersion to 3.3(-2.5)(+9.1) x 10(5)M(circle dot) (M/L-V = 75(-58)(+230)[M/L-V](circle dot)). From the stacked spectrum of the five central members we estimate a mean metallicity of [Fe/H]= -2.0 +/- 0.2 dex. Thus, with respect to dwarf spheroidals of similarluminosity, Leo V is slightly less massive and slightly more metal rich. Since we resolve the central velocity dispersion only marginally, we do not rule out the possibility that Leo V is a diffuse star cluster devoid of dark matter. The wide separation of its two outer members implies Leo V is losing mass; however, its large distance (D similar to 180 kpc) is difficult to reconcile with MW tidal stripping unless the orbit is very radial.