We have obtained Keck Low Resolution Imaging Spectrograph images in V and I of the newly discovered Local Group dwarf galaxies Pegasus dSph and Cassiopeia dSph and their surrounding field .
The first stellar luminosity functions and color-magnitude diagrams are presented for stars with V \lesssim 25 and I \lesssim 24 .
The distances to the new dwarfs are estimated from the apparent I mag of the tip of the red giant branch to be : D _ { MW } ( Peg dSph ) = 830 \pm 80 kpc and D _ { MW } ( Cas dSph ) = 760 \pm 70 kpc , consistent with their belonging to the extended M31 satellite system .
Both galaxies are dwarf spheroidals ( dSphs ) with red giant branch morphologies indicating predominantly old stellar populations and estimated mean metallicities , \langle [ Fe / H ] \rangle , of -1.3 \pm 0.3 for Peg dSph and -1.4 \pm 0.3 for Cas dSph .
Their central surface brightness– \langle [ Fe / H ] \rangle –absolute magnitude relationship follows that of other Local Group dSphs , dwarf ellipticals , and dwarf irregulars .
In contrast to four out of nine Milky Way dSphs ( the four that lie beyond D _ { MW } = 100 kpc ) , none of the six known M31 dSphs appears to have a dominant intermediate-age population .