Hostname: page-component-cd9895bd7-8ctnn Total loading time: 0 Render date: 2024-12-26T03:37:20.226Z Has data issue: false hasContentIssue false
  • English
  • Français

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

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

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 

References

Cid-Fernandes, R., Dottori, H., Gruenwald, R., & Viegas, S.M. 1992, MNRAS, 255, 165 CrossRefGoogle Scholar
Davidson, K., & Kinman, T.D. 1985, ApJS, 58, 321 Google Scholar
Dinerstein, H.L., & Shields, G.A. 1986, ApJ, 311, 45 CrossRefGoogle Scholar
Ferland, et al. 1995, in The Analysis of Emission Lines, STScI Symp. Ser. 8, ed. Williams, R.E. & Livio, M. (Cambridge: Cambridge University Press), 143 Google Scholar
Izotov, Y.I., Thuan, T.X., & Lipovetsky, V.A. 1994, ApJ, 435, 647 CrossRefGoogle Scholar
Izotov, Y.I., Thuan, T.X., & Lipovetsky, V.A. 1997, ApJS, 108, 1 CrossRefGoogle Scholar
Izotov, Y.I. & Thuan, T.X. 1998, ApJ, 500, 188 Google Scholar
Mathis, J.S. 1982, ApJ, 261, 195 CrossRefGoogle Scholar
Olive, K.A., Skillman, E., & Steigman, G. 1997, ApJ, 483, 788 CrossRefGoogle Scholar
Olive, K. A., &, Steigman, G. 1995, ApJS, 97, 49 CrossRefGoogle Scholar
Pagel, B.E.J., Somonson, E.A., Terlevich, R.J. & Edmunds, M. 1992, MNRAS, 255, 325 Google Scholar
Peimbert, M. & Costero, R. 1969, Bol. Obs. Tonantziltla y Tacubaya, 5, 3 Google Scholar
Peimbert, M. & Torres-Peimbert, S. 1977, MNRAS, 179, 217 Google Scholar
Pena, M. 1986, PASP, 98, 1061 CrossRefGoogle Scholar
Pequignot, 1986, Workshop on Model Nebulae, ed. Pequignot, D. (Meudon, Observatoire de Paris-Meudon)Google Scholar
Skillman, E., Terlevich, R.J., Kennicutt, R.C., Garnett, D.R., & Terlevich, E. 1994, ApJ, 431, 172 Google Scholar
Skillman, E., Terlevich, E., & Terlevich, R.J. 1998, Sp. Sci. Rev, 84, 105 Google Scholar
Stasinska, G. 1980, A&A, 84, 320 Google Scholar
Stasinska, G. 1982, A&AS., 41, 513 Google Scholar
Viegas, S.M., Gruenwald, R., & Steigman, G. 2000, ApJ (in press) Google Scholar
Vilchez, J.M. & Pagel, B.E.J. 1988, MNRAS, 231, 257 Google Scholar