We report the results of a spectroscopic study of the Boötes ( Boo ) dwarf spheroidal ( dSph ) galaxy carried out with the WIYN telescope and the Hydra multifiber spectrograph .
Radial velocities have been measured for 58 Boo candidate stars selected to have magnitudes and colors consistent with its red and asymptotic giant branches .
Within the 13′ half-light radius , seven members of Boo yield a systemic velocity of V _ { r } = 95.6 \pm 3.4 km s ^ { -1 } and a velocity dispersion of \sigma _ { o } = 6.6 \pm 2.3 km s ^ { -1 } .
This implies a mass on the order of 1 \times 10 ^ { 7 } M _ { \sun } , similar to the inferred masses of other Galactic dSphs .
Adopting a total Boo luminosity of L = 1.8 \times 10 ^ { 4 } L _ { \sun } to 8.6 \times 10 ^ { 4 } L _ { \sun } implies M / L \sim 610 to 130 , making Boo , the most distorted known Milky Way dwarf galaxy , potentially also the darkest .
From the spectra of Boo member stars we estimate its metallicity to be [ Fe/H ] \sim - 2.5 , which would make it the most metal poor dSph known to date .