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E.K. Grebel, P. Guhathakurta (UCSC)
We have obtained Keck Low Resolution Imaging Spectrograph images in V and I of the newly discovered Local Group dwarf galaxies Pegasus Dw and Cassiopeia Dw and their surrounding field. We present the first stellar luminosity functions and color-magnitude diagrams for stars with V\leq25 and I\leq24. The distances to the new dwarfs estimated from the apparent tip of the red giant branch I magnitude are 780±0 kpc (Peg Dw) and 710±5 kpc (Cas Dw), 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, estimated mean metallicities of -1.2±.3 dex (Peg Dw) and -1.1±.3 (Cas Dw), and possible abundance spreads of \approx1 dex. They lie near the upper envelope of the central surface brightness-vs-<[Fe/H]> relation for dSphs, dwarf ellipticals, and dwarf irregulars. In contrast to the four (out of nine) Milky Way dSphs beyond D>100 kpc, which are dominated by intermediate-age populations, none of the six known M31 dSphs appears to have a substantial intermediate-age population.