Emission-line spectroscopy of HII regions in irregular and blue compact dwarf galaxies

We present reddenings and abundances of 189 H II regions measured from 203 emission-line spectra in a sample of 65 irregular (Im), blue compact dwarf (BCD), and Sm galaxies. In most of these spectra we measure [O III] lambda 5007, H beta, [N II] lambda 6584, and [S II] lambda lambda 6717, 6731; in 2 4 spectra we measure [O II] lambda 3727; and in five we measure [O III] lam bda 4363. The internal reddenings of the galaxies are used to determine whe ther redder irregular galaxies are also dustier than bluer irregulars. We f ind that the range in optical broadband colors among Im galaxies is most li kely dominated by differences in the contributions of the massive star popu lation or the effects of abundances, while the range in colors of BCDs does show evidence consistent with a contribution from dustiness. We use the ab undances to confirm that our sample of BCD galaxies, selected to be compara ble to Im systems in other global properties, are also comparable in abunda nces and, hence, evolutionary status. Finally, we explore relationships bet ween abundances and other global galactic properties and find few convincin g correlations. However, bluer galaxies tend to be more metal-poor. There i s a slight trend of higher relative gas content with lower abundances among the BCD sample, but not in the Im sample. The difference could be due to a difference in gas distributions and the fraction of total gas that is acti vely participating in the chemical evolution of the galaxy. In addition, ou r BCD, but not our Im, sample of galaxies are consistent by themselves with the galactic luminosity-metallicity relationship determined by others, but the Im sample is consistent with the general trend seen over a large basel ine when combined with spiral galaxies. However, the scatter is large.