2016MNRAS.457.3678P

Simple relations for deriving the oxygen abundance in H ii regions with intensities of the three strong emission lines R₂, R₃, and N₂ (R calibration) or S₂, R₃, and N₂ (S calibration) in their spectra are suggested. A sample of 313 reference H ii regions of the counterpart method (C method) is used as calibrating data points. Relations for the determination of nitrogen abundances, the R calibration, are also constructed. We find that the oxygen and nitrogen abundances in high-metallicity H ii regions can be estimated using the intensities of the two strong lines R₂ and N₂ (or S₂ and N₂ for oxygen) only. The corresponding two-dimensional relations are provided. There are considerable advantages of the suggested calibration relations as compared to the existing ones. First, the oxygen and nitrogen abundances estimated through the suggested calibrations agree with the T_e-based abundances within ∼0.1 dex over the whole metallicity range, i.e. the relative accuracy of the calibration-based abundances is 0.1 dex. Although we constructed distinct relations for high- and low-metallicity objects, the separation between these two can be simply obtained from the intensity of the N₂ line. Moreover, the applicability ranges of the high- and low-metallicity relations overlap for adjacent metallicities, i.e. the transition zone disappears. Secondly, the oxygen abundances produced by the two suggested calibrations are in remarkable agreement with each other. In fact, the R-based and S-based oxygen abundances agree within ∼0.05 dex in the majority of cases for more than three thousand H ii region spectra.