Spectroscopy of candidate metal-deficient galaxies with the 6-m telescope

We present the first results of our program of search for the most metal-deficient blue compact galaxies (BCGs) carried out with the 6-m Special Astrophysical Observatory telescope. The results of spectrophotometry are presented and discussed for ten galaxies from the Case and Hamburg/SAO surveys. The selection of candidates, observations, and data reduction are described in detail. For all the galaxies studied, we measured the intensity of the O III] λ4363 Å emission line, which allows us to properly determine the temperatures of H II regions and to deduce elemental abundances. We measured the intensities of all the detected emission lines in H II regions of the galaxies under study and determined the abundances of oxygen and neon in them and in some of these galaxies, of other elements (N, S, He, Ar, and Fe). The oxygen abundance log (O/H)+12 in six galaxies was derived with an error ≤0.1 dex. Six of the ten galaxies studied turned out to be metal-poor with an oxygen abundance ≤1/10 of its solar value i.e., 12+log(O/H)≤7.92]. HS 0837+4717 with 12+log(O/H) ≤7.7 is one of the most metal-poor galaxies in this sample and one of the candidates for young galaxies. Low-contrast, broad emission components of the nebular O III]λ4959 and 5007 Å lines were detected in its spectrum, suggesting high velocities of gas motions in this galaxy.