The history of star formation was successfully analyzed for the first time based on the spectra of the stellar population of dwarf galaxies of low surface brightness outside the Local Group. We have investigated the stellar population of two dwarf spheroidal galaxies KDG61 and KDG64 in the central part of a close group of galaxies M81. The integral spectra were obtained on the 6-m BTA telescope. Direct imaging performed on the Hubble Space Telescope (HST /ACS) was as well used for the quantitative analysis of the history of star formation. Both approaches have yielded consistent results. These galaxies are dominated by the old stellar population (12-14 billion years) of low metallicity ([Fe/H] ~ -1.5). Both galaxies reveal stars aged from 1 to 4 billion years. This population demonstrates a slight enrichment of metals. No significant radial gradient in age or metallicity was observed in the resolved stellar population.
Makarova L., Makarov D. in collaboration with M. Koleva and Ph. Prugniel (Observatory of Lyon, France).