The High Resolution Echelle Spectrometer on the Keck I telescope has been used to measure nine radial velocities having a median precision of \simeq 2 km s ^ { -1 } for seven red giants belonging to the isolated dwarf spheroidal galaxy Andromeda II ( And II ) .
We find a weighted mean radial velocity of { \overline { v } } _ { r } = –188 \pm 3 km s ^ { -1 } and a central velocity dispersion of \sigma _ { 0 } = 9.3 ^ { +2.7 } _ { -2.6 } km s ^ { -1 } .
There may be evidence for a radial velocity gradient across the face of the galaxy , although the significance of this result is low due to the small number of stars having measured velocities .
Our best estimate for the global mass-to-light ratio of And II is M / L _ { V } = 20.9 ^ { +13.9 } _ { -10.1 } M _ { \odot } / L _ { V, { \odot } } .
This value is similar to those of several Galactic dwarf spheroidal galaxies and is consistent with the presence of a massive dark halo in And II .