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Among ‘empirical’ methods of estimating oxygen abundances in extragalactic H ii regions, the use of the ratio of nebular lines of O iii and N ii, first introduced by Alloin et al., is reappraised with modern calibration data and shown to have certain advantages over R23≡ (O ii+O iii)/Hβ and N2 ≡N iiλ6583/Hα, particularly when applied to star-forming galaxies at high redshifts.
Pettini et al. (Fri,) studied this question.