Chemical Abundances In Seven Metal-Poor H Ii Regions And A Determination Of The Primordial Helium Abundance

We conducted a long-slit spectrophotometry analysis to obtain the chemical abundances of seven metal-poor HII regions in three galaxies: UM 160, UM 420, and TOL 0513-393. The data have been taken with the Focal Reducer Low Dispersion Spectrograph 1 (FORS1) at the 8.2-m Very Large Telescope. We derived the physical conditions and the chemical abundances of N, O, Ne, S, Ar, and Cl. We also performed a detailed analysis that involves abundance determinations using the t(2) formalism. Based on Hei recombination line intensity ratios, together with the {\sc HELIO 14} code, we derived the abundance of He. In addition, for a value Delta Y/Delta Z(o) = 3.3 +/- 0.7 , we have estimated that the primordial helium abundance by mass is Y-P = 0.2448 +/- 0.0033. This value agrees with values derived from Standard Big Bang Nucleosynthesis and with other recent determinations of Y-P.