EDP Sciences
Free access
Issue
A&A
Volume 369, Number 2, April II 2001
Page(s) 594 - 604
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20010079


A&A 369, 594-604 (2001)
DOI: 10.1051/0004-6361:20010079

On the oxygen abundance determination in HII regions.

High-metallicity regions
L. S. Pilyugin

Main Astronomical Observatory of National Academy of Sciences of Ukraine, Goloseevo, 03680 Kiev-127, Ukraine

(Received 26 October 2000 / Accepted 22 December 2000)

Abstract
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 ( $[{\rm OII}] \lambda \lambda 3727, 3729$ and $[{\rm OIII}] \lambda \lambda 4959, 5007$) 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 ( $12+{\rm log O/H} \leq 7.95$, the lower branch of the O/H -R23 diagram). The high-metallicity HII regions ( $12+{\rm log O/H} \geq
8.2$, the upper branch of the O/H -R23 diagram) are considered in the present study. A relation of the type ${\rm O/H}=f(P, R_{23}$) between oxygen abundance and the value of abundance index R23, introduced by Pagel et al. (1979), and the excitation parameter P (which is defined here as the contribution of the radiation in $[{\rm OIII}] \lambda \lambda 4959, 5007$ 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 ($T_{\rm e}$-method). By comparing oxygen abundances in high-metallicity HII regions derived with the $T_{\rm e}$-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 ~0.08 dex) and is comparable to that of the $T_{\rm e}$-method. A relation of the type $T_{\rm e}=f(P, R_{23}$) between electron temperature and the values of abundance index R23 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 ~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.


Key words: ISM: HII regions -- galaxies: abundances -- galaxies: ISM -- galaxies: spiral

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