Hα Survey of low-mass satellites of the neighboring galaxies M31 and M81

Images have been obtained at the 6-m telescope at the Special Astrophysical Observatory (SAO) of the Russian Academy of Sciences in the H alpha line and in the continuum for 20 dwarf spheroidal satellites of M31: And XI-And XXX, plus the distant Globular cluster Bol 520. Their star formation rates (SFR) are estimated using the H alpha flux and the ultraviolet FUV flux measured with the GALEX space telescope. Most of the dSph satellites of M31 have extremely low star formation rates with a characteristic upper limit of SFR similar to 5 x 10(-7). We have made similar estimates of SFR from the H alpha and FUV fluxes for 13 galaxies with low surface brightness recently discovered in the neighborhood of M81. Eleven of them are physical satellites of M81 with typical SFR < 1 x 10(-5). The median stellar masses of these satellites of M31 and M81 are 0.9 and 1.9 million solar masses, respectively. Our H alpha observations place a 2-3 times stricter limit on the value of SFR than the data from the GALEX satellite, with a substantially higher (3-5 times) angular resolution.