Oxygen Abundances and Chemical Evolution in Low Surface Brightness Galaxies

We report the oxygen abundances of the HII regions of a sample of low surface brightness (LSB) galaxies. We provide analytic functions describing the McGaugh (1991) calibration of the R_23 method. We use this and the equivalent width (EW) method to determine oxygen abundances, and also make direct estimates in a few cases where the temperature sensitive [OIII] 4363 line is available. We find LSB galaxies to be metal poor, consistent with the L-Z relation of other galaxies. The large gas mass fractions of these objects provide an interesting test of chemical evolution models. We find no obvious deviation from the closed-box model of galactic chemical evolution. Based on our abundance and gas mass fraction measurements, we infer that LSB galaxies are not fundamentally different than other galaxy types but are perhaps at an early stage of evolution.