On the relationship between auroral and nebular oxygen line intensities in spectra of HII regions

Abstract

We investigate relationships between observed auroral and nebular oxygen line fluxes in spectra of HII regions. We find a relation that is metallicity-dependent at low metallicities, but becomes independent of metallicity (within the uncertainties of the available data) above 12+logO/H ~ 8.25, i.e. there is one-to-one correspondance (the ff - relation) between auroral and nebular oxygen line fluxes in spectra of high-metallicity HII regions. The ff - relation allows one to estimate the flux in the auroral line from strong oxygen line measurements. This solves the problem of the electron temperature (and, consequently, abundance) determination in high-metallicity HII regions. The ff - relation confirms the basic idea of the empirical method, proposed by Pagel et al. (1979) a qurter of a century ago, that the oxygen abundance in HII region can be estimated from the strong oxygen lines measurements only.