Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990apj...362..100c&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 362, Oct. 10, 1990, p. 100-106.
Astronomy and Astrophysics
Astrophysics
15
Electron Density (Concentration), Electron Energy, Galactic Structure, H Ii Regions, Oxygen Ions, Astronomical Models, Density Distribution, Emission Spectra, H Alpha Line, Line Spectra
Scientific paper
Most of the lowest-metallicity galactic systems known have emission-line ratios that are not well-fitted by a simple H II region model. These objects are similar to the low-abundance H II galaxy I Zw 18 in that the observed F(3727 A)/F(H-beta) does not agree with the predictions of models that fit F(4363 A)/F(H-beta), and F(4363)/F(4959, 5007), casting doubt on the oxygen abundance estimated from the line ratios. Here, the observed emission-line ratios of I Zw 18 are compared with those of model nebulae incorporating a density gradient. An attempt is made to develop a self-consistent model capable of explaining all existing observations of I Zw 18 and to investigate the possibility that the true oxygen abundance of this object is higher than the very low value obtained from the estimated electron temperature of O(2+).
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