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2005MNRAS.360..227M - Mon. Not. R. Astron. Soc., 360, 227-235 (2005/June-2)
The effects of clumping on derived abundances in HII regions.
MATHIS J.S. and WOOD K.
Abstract (from CDS):
Clumped models have different ionic abundances than uniform. For hot stars, (He0/H+) is 2-3 per cent, much larger than with uniform models. This amount of He0 is independent of metallicity and so impacts the determination of the primordial abundance of He. The total abundances of O, Ne and S obtained by the usual methods of analysis, using T([OIII]) for high stages of ionization and T([NII]) for low, are about as accurate for clumped models as for uniform, and within ∼20 per cent of the true values. If T([OIII]) is used for analysing all ions, the derived (O/H) is ∼40-60 per cent too large for cool stars but is good for hot stars. Uniform models have similar errors, so the clumping does not change the accuracy of abundance analysis.
The physical causes of the ionic abundance errors are present in real nebulae. In clumped models, helium ionizing radiation from zones of high ionization (low He0 and low ultraviolet opacity) can penetrate nearby regions near the edge of the ionized zone. This effect allows He0 to absorb more stellar photons than in uniform or radially symmetrical geometries. In turn, these absorptions compete with O+, etc., for those energetic stellar photons.
Abstract Copyright: 2005 RAS
Journal keyword(s): radiative transfer - ISM: general - HII regions - cosmology: miscellaneous
Simbad objects: 2
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