Combined color indices and photometric structures of the galaxies NGC 834 and NGC 1134

Surface BVRI photometry is presented for two spiral galaxies with a complex photometric structure: NGC 834 and NGC 1134. We propose to introduce the combined color indices Q _BVI and Q _VRI to investigate the photometric structure of the galaxies. These color indices depend only slightly on selective absorption, which allows them to be used to study the photometric structure of “dusty” galaxies. Evolutionary stellar-population models show that Q _BVI is most sensitive to the presence of blue stars, while Q _VRI depends on local Hα equivalent width. A ring with active star formation manifests itself on the Q _BVI map for NGC 834 at a distance of ～15 from its center, and a spiral structure shows up on the Q _VRI map for NGC 1134 in its inner region. The Q _BVI –Q _VRI diagram can provide information about the current stage of a star's formation in various galactic regions. A comparison of the color indices for the galaxies with their model values allows us to estimate the color excesses and extinction in various galactic regions.