Abundance determinations in H II regions

Model fitting versus –method

Main Astronomical Observatory of National Academy of Sciences of Ukraine, 27 Zabolotnogo str., 03680 Kiev, Ukraine

Corresponding author: pilyugin@mao.kiev.ua

Received: 30 September 2002
Accepted: 18 October 2002

Abstract

The discrepancy between the oxygen abundances in high-metallicity H ii regions determined through the T_e–method (and/or through the corresponding “strong lines – oxygen abundance” calibration) and that determined through the model fitting (and/or through the corresponding “strong lines – oxygen abundance” calibration) is discussed. It is suggested to use the interstellar oxygen abundance in the solar vicinity, derived with very high precision from the high-resolution observations of the weak interstellar OIλ1356 absorption lines towards the stars, as a “Rosetta stone” to verify the validity of the oxygen abundances derived in H ii regions with the T_e–method at high abundances. The agreement between the value of the oxygen abundance at the solar galactocentric distance traced by the abundances derived in H ii regions through the T_e–method and that derived from the interstellar absorption lines towards the stars is strong evidence in favor of that i) the two-zone model for T_e seems to be a realistic interpretation of the temperature structure within H ii regions, and ii) the classic T_e–method provides accurate oxygen abundances in H ii regions. It has been concluded that the “strong lines – oxygen abundance” calibrations must be based on the H ii regions with the oxygen abundances derived with the T_e–method but not on the existing grids of the models for H ii regions.