Abundance determination in H ii regions from spectra without the [O ii]λ3727+λ3729 line

We suggest an empirical calibration for the determination of oxygen and nitrogen abundances and electron temperature in H ii regions in which the [O ii]lambda 3727+lambda 3729 line (R-2) is not available. The calibration is based on the strong emission lines of O++, N+ and S+ (NS calibration) and derived using the spectra of H ii regions with measured electron temperatures as calibration data points. The NS calibration makes it possible to derive abundances for H ii regions in nearby galaxies from Sloan Digital Sky Survey (SDSS) spectra in which the R-2 line is out of the measured wavelength range, but it can also be used for oxygen and nitrogen abundance determinations in any H ii region independently of whether the nebular oxygen line [O ii]lambda 3727+lambda 3729 is available or not. The NS calibration provides reliable oxygen and nitrogen abundances for H ii regions over the whole range of metallicities.