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Keywords:

  • methods: data analysis;
  • techniques: spectroscopic;
  • ISM: abundances;
  • H ii regions;
  • galaxies: abundances

ABSTRACT

In an attempt to remove the systematic errors which have plagued the calibration of the H ii region abundance sequence, we have theoretically modelled the extragalactic H ii region sequence. We then used the theoretical spectra so generated in a double-blind experiment to recover the chemical abundances using both the classical electron temperature + ionization correction factor technique and the technique which depends on the use of strong emission lines (SELs) in the nebular spectrum to estimate the abundance of oxygen. We find a number of systematic trends, and we provide correction formulae which should remove systematic errors in the electron temperature + ionization correction factor technique. We also provide a critical evaluation of the various semi-empirical SEL techniques. Finally, we offer a scheme which should help to eliminate systematic errors in the SEL-derived chemical abundance scale for extragalactic H ii regions.