Abstract
In this paper we present the results of observations of 17 H II regions in thirteen galaxies from the SIGRID sample of isolated gas-rich irregular dwarf galaxies. The spectra of all but one of the galaxies exhibit the auroral [O III] 4363 angstrom line, from which we calculate the electron temperature, T-e, and gas-phase oxygen abundance. Five of the objects are blue compact dwarf galaxies, of which four have not previously been analyzed spectroscopically. We include one unusual galaxy which exhibits no evidence of the [N II]lambda lambda 6548,6584 angstrom lines, suggesting a particularly low metallicity (< Z(circle dot) /30). We compare the electron temperature based abundances with those derived using eight of the newstrong-line diagnostics presented by Dopita et al. Using amethod derived from first principles for calculating total oxygen abundance, we show that the discrepancy between the T-e-based and strong-line gas-phase abundances have now been reduced to within similar to 0.07 dex. The chemical abundances are consistent with what is expected from the luminosity-metallicity relation. We derive estimates of the electron densities and find them to be between similar to 5 and similar to 100 cm(-3). We find no evidence for a nitrogen plateau for objects in this sample with metallicities 0.5> Z(circle dot) > 0.15.