On the oxygen abundance determination in HII regions. High-metallicity regions

This is our second paper devoted to the problem of line intensity - oxygen abundance calibration starting from the idea of McGaugh (1991) that the strong oxygen lines ([OII]lambda lambda 3727, 3729 and [OIII]lambda lambda 4959, 5007) contain the necessary information to determine accurate abundances in HII regions. In the previous study (Pilyugin 2000) the corresponding relations were obtained for the low-metallicity HII regions (12 + log O/H less than or equal to 7.95, the lower branch of the O/H - R-23 diagram). The high-metallicity HII regions (12 + log O/H greater than or equal to 8.2, the upper branch of the O/H - R-23 diagram) are considered in the present study. A relation of the type O/H = f(P, R-23) between oxygen abundance and the value of abundance index R-23, introduced by Pagel et al. (1979), and the excitation parameter P (which is defined here as the contribution of the radiation in [OIII]lambda lambda 4959, 5007 lines to the total oxygen radiation) has been derived empirically using the available oxygen abundances determined via measurement of a temperature-sensitive line ratio [OIII]-4959,5007/[OIII]4363 (T-e-method). By comparing oxygen abundances in high-metallicity HII regions derived with the T-e-method and those derived with the suggested relations (P-method), it was found that the precision of oxygen abundance determination with the P-method is around 0.1 dex (the mean difference for the 38 HII regions considered is similar to0.08 dex) and is comparable to that of the T-e-method. A relation of the type T-e = f(P, R-23) between electron temperatures and the values of abundance index R-23 and the excitation parameter P was derived empirically using the available electron temperatures determined via measurement of temperature-sensitive line ratios. The maximum value of differences between electron temperatures determined via measurement of temperature-sensitive line ratios and those derived with the suggested relation is around 1000 K for HII regions considered here, the mean value of differences for 38 HII regions is similar to 500 K, which is the same order of magnitude as the uncertainties of electron temperature determinations in high-metallicity HII regions via measured temperature-sensitive line ratios.