The oxygen abundance of nearby galaxies from sloan digital sky survey spectra

We have derived the oxygen abundance for a sample of nearby galaxies in Data Release 5 of the Sloan Digital Sky Survey (SDSS) that possess at least two independent spectra of one or several H II regions with a detected [O III] lambda 4363 auroral line. Since, for nearby galaxies, the [O II] lambda 3727 nebular line is out of the observed wavelength range, we propose a method to derive (O/H)(ff) abundances using the classic T-e method coupled with the flux-flux (ff) relation. (O/H)(7325) abundances have also been determined, based on the [O II] lambda lambda 7320, 7330 line intensities and using a small modification of the standard T-e method. The (O/H)(ff) and (O/H)(7325) abundances have been derived with both the one- and two-dimensional t(2)- t(3) relations. It was found that the (O/H)(ff) abundances derived with the parametric two-dimensional t(2)-t(3) relation are the most reliable. Oxygen abundances have been determined in 29 nearby galaxies on the basis of 84 individual abundance determinations in H II regions. Because of our selection methods, the metallicity of our galaxies lies in the narrow range 8.2 less than or similar to 12 + log(O/H) less than or similar to 8.4. The radial distribution of oxygen abundances in the disk of the spiral galaxy NGC 4490 is determined for the first time.