Andromeda X, a new dwarf spheroidal satellite of M31:: Photometry

We report the discovery of Andromeda X, a new dwarf spheroidal satellite of M31, based on stellar photometry from the Sloan Digital Sky Survey. Using follow-up imaging data we have estimated its distance and other physical properties. We find that Andromeda X has a dereddened central surface brightness mu(V,0) similar to 26.7 mag arcsec(-2) and a total apparent magnitude of V-tot similar to 16.1 which at the derived distance modulus, (m - M)(0) similar to 24.12-24.34, yields an absolute magnitude of M-V similar to -8.1 +/- 0.5; these values are quite comparable to those of Andromeda IX, a previously discovered low-luminosity M31 satellite. The discoveries of Andromeda X and of numerous other extremely faint satellites around M31 and the Milky Way in the past few years suggest that such objects may be plentiful in the Local Group.