Oxygen Abundance and Stellar Populations in the Three Most Metal-Deficient Emission-Line Galaxies Known in the Local Universe: SBS 0335-052,E, SBS 0335-052 W and I Zw 18

We present new spectroscopic observations of the system of the two blue compact dwarf (BCD) galaxies SBS 0335-052 W and SBS 0335-052 E with the 3.6m ESO telescope. The oxygen abundance in SBS 0335-052 W was determined to be 12 + log(O/H) = 7.13±0.08, confirming that this galaxy is the most metal-deficient emission-line galaxy known. We find that the oxygen abundance in SBS 0335-052 E varies from region to region in the range from 7.20 to 7.31, suggesting the presence of an abundance gradient over a spatial scale of ~1 kpc. Signatures of early carbon-type Wolf-Rayet stars are detected in cluster #3 of SBS 0335-052 E, corresponding to the emission of 20 to 130 WC4 stars, depending on the adopted luminosity of a single WC4 star in the Civ λ4658 emission line (Papaderos et al. 2006).