Publication Date:
2014-05-29
Description:
The derivation of abundances in gaseous nebulae ionized by massive stars using optical collisionally excited emission lines is studied in this work, comparing the direct or T e method with updated grids of photoionization models covering a wide range of input conditions of O/H and N/O abundances and ionization parameter. The abundances in a large sample of compiled objects with at least one auroral line are re-derived and later compared with the 2 -weighted-mean abundances from the models. The agreement between the abundances using the two methods both for O/H and N/O is excellent with no additional assumptions about the geometry or physics governing the H ii regions. Although very inaccurate model-based O/H are obtained when no auroral lines are considered, this can be overcome assuming empirical laws between O/H, log U , and N/O to constrain the considered models. In this way, for 12+log(O/H) 〉 8.0, a precision better than 0.1 dex consistent with the direct method is attained. For very low Z , models give higher O/H values and a high dispersion, possibly owing to the contamination of the low-excitation emission lines. However, in this regime, the auroral lines are usually well detected. The use of this procedure, in a publicly available script, hii-chi-mistry , leads to the derivation of abundances in faint-/high-redshift objects consistent with the direct method based on collisionally excited lines.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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