H II region abundances - Model oxygen line ratios
Oct, 199111 pages
Published in:
- Astrophys.J. 380 (1991) 140-150
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Abstract: (ADS)
An extensive homogeneous grid of H II region models is presented. They are specified by three parameters: the shape of the ionizing spectrum, the geometry of the nebula, and the abundance of the chemical elements in the gas. It is found that the behavior of the strong oxygen lines can be modeled by taking proper account of the softening of the ionizing spectra produced by stars of increasing metallicity. No metallicity dependence of the IMF is found necessary to explain the systematic softening of stellar spectra with increasing metallicity. It results naturally from the stellar mass-temperature-metallicity relation. No convincing evidence is found for a correlation between the ionization parameter and metallicity which cannot be attributed to observational selectional effects. It is suggested that the extragalactic H II region excitation sequence is purely a metallicity effect.References(0)
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