On the oxygen abundance determination in HII regions: the problem of the line intensities -- oxygen abundance calibration

TL;DR

This paper develops a new empirical method for determining oxygen abundance in HII regions using strong line intensities and excitation parameters, improving calibration accuracy across different metallicities.

Contribution

It introduces a novel oxygen abundance calibration based on excitation parameters and compares it with existing calibrations, enhancing accuracy in HII region analysis.

Findings

The new calibration aligns with previous methods for oxygen-rich regions.

Excitation parameters p2 and p3 effectively account for R23 variations.

The calibration is consistent with earlier models but offers improved precision.

Abstract

The problem of the line intensities -- oxygen abundance calibration has been considered. We confirm the idea of McGaugh (1991) that the strong oxygen lines ([OII] 3727, 3729 and [OIII] 4959, 5007) contain the necessary information for determination of accurate abundances in low-metallicity (and may be also in high-metallicity) HII regions. It has been found that the excitation parameters p3 or p2 (which are defined here as contributions of the radiation in [OIII] 4959, 5007 lines and in [OII] 3727, 3729 lines to the "total" oxygen radiation respectively) allow to take into account the variations in R23 values among HII regions with a given oxygen abundance. Based on this fact a new way of the oxygen abundance determination in HII regions has been constructed and corresponding relations between line intensities and the oxygen abundance have been derived empirically using the available oxygen abundances determined via measurement of temperature-sensitive line ratios. In parallel a new R23 calibration has been derived on the base of recent data and compared to previous calibrations. For oxygen-rich HII regions the present R23 calibration is close to that of Edmunds and Pagel (1984): their calibration has the same slope but is shifted towards higher oxygen abundances by around 0.07 dex as compared to the present calibration.