Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1988
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988apj...335..644c&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 335, Dec. 15, 1988, p. 644-657.
Astronomy and Astrophysics
Astrophysics
85
Dwarf Galaxies, Galactic Structure, H Ii Regions, Ionizing Radiation, Stellar Coronas, Abundance, Emission Spectra, Line Spectra, Oxygen Spectra
Scientific paper
The temperature of the ionizing radiation, Tion, and the mean nebular ionization parameter, U, are measured for a sample of 45 H II galaxies with estimated oxygen abundances in the range -4.9 ⪉ log O/H ⪉ -3.6. A simple, Strömgren sphere model fits very well all but three of the objects. The data show that the maximum value of Tion at a particular abundance increases smoothly with decreasing O/H, from ≅45,500K at a true log O/H of -3.6 to ≅63,000K at log O/H = -4.4. The maximum value of U at each abundance also shows a shallow inverse trend with O/H. The fact that Tion varies systematically with abundance rules out differences in nebular geometry as the primary cause of the line ratio gradients observed among H II galaxies and, by analogy, giant H II regions in spiral galaxies.
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