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Inhomogeneous H II Regions and the Helium Abundance

Published online by Cambridge University Press:  25 May 2016

S. M. Viegas  and
R. Gruenwald
S. M. Viegas
Affiliation:
IAG-USP; Av. Miguel Stefano, 4200; 04301-904 São Paulo, SP, Brazil
R. Gruenwald
Affiliation:
IAG-USP; Av. Miguel Stefano, 4200; 04301-904 São Paulo, SP, Brazil

Abstract

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When calculating the helium (4He) abundance in low metallicity H ii regions, the ionization correction factor (icf) for unseen neutral helium (and hydrogen) is usually assumed to be unity. In this paper, we explore this factor for H ii regions ionized by young stellar clusters. Our main result is that icf < 1 for homogeneous H ii regions and, that the effect of density condensations in the H ii regions is to further reduce the icf. For icf < 1, the primordial helium abundance inferred from observations of low-metallicity, extragalactic H ii regions is decreased.

Type
3. Abundances of D, 3He and 4He
Information
Symposium - International Astronomical Union , Volume 198: The Light Elements and their Evolution , 2000 , pp. 188 - 193
Copyright
Copyright © Astronomical Society of the Pacific 2000 

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