scholarly journals Ionization Corrections for Low‐Metallicity HiiRegions and the Primordial Helium Abundance

2000 ◽  
Vol 531 (2) ◽  
pp. 813-819 ◽  
Author(s):  
Sueli M. Viegas ◽  
Ruth Gruenwald ◽  
Gary Steigman
Keyword(s):  
Helium Abundance ◽  
Low Metallicity ◽  
Primordial Helium

scholarly journals Blue Compact Galaxies and the Primordial Helium Abundance Determination

1998 ◽  
Vol 11 (1) ◽  
pp. 137-138
Author(s):  
Y.I. Izotov ◽  
T.X. Thuan
Keyword(s):  
Linear Regression ◽  
H Ii Regions ◽  
Helium Abundance ◽  
Line Intensities ◽  
Low Metallicity ◽  
Physical Effects ◽  
Primordial Helium ◽  
Compact Galaxies ◽  
Abundance Determination

Abstract We use a sample of 45 low-metallicity H II regions to determine the primordial helium abundance Yp. We have carefully investigated the physical effects which may make the He I line intensities deviate from their recombination values such as collisional and fluorescent enhancements, underlying He I stellar absorption and absorption by Galactic interstellar Na, I. By extrapolating the Y vs. O/H linear regression to O/H = 0, we obtain Yp = 0.245±0.002. Our Yp gives 0.06±0.01.

The primordial helium abundance determination using multicomponent photoionization modelling of low-metallicity H II regions

2018 ◽  
Vol 8 (1) ◽  
pp. 16-23
Author(s):  
I. Koshmak ◽  
B. Melekh
Keyword(s):  
Chemical Compositions ◽  
H Ii Regions ◽  
Helium Abundance ◽  
Rotating Stars ◽  
Chemical Abundances ◽  
Free Expansion ◽  
Outer Component ◽  
Low Metallicity ◽  
H Ii Region ◽  
Primordial Helium

The method for the multicomponent photoionization modelling (MPhM) of low-metallicity H II regions surrounding the starburst region was developed. The internal structure of the H II region has been determined using the evolutionary modelling of the superwind bubble surrounding the star-forming region. Models of Chevalier and Clegg (1985) and Weaver et al. (1977) have been used to determine the radial distribution of the gas density, the velocity of gas layers, and the temperature within internal components (the region of the superwind free expansion and the cavity, respectively). The chemical abundances in region of the superwind free expansion were obtained from the evolutionary population synthesis with including of rotating stars. The chemical abundances within cavity were defined by averaging over mass the chemical compositions of mixture of the abundances of gas from superwind and ones within outer component, because of gas evaporation from external component into the cavity. External components of our models describe a high-density, thin shell of gas formed by superwind shock and a typical undisturbed hydrodynamically H II region, respectively. Evolutionary grids of multicomponent low-metallicity models are calculated. A comparative analysis of the results of their calculation with the observed data has been carried out. The ionic abundances averaged over modelling volume as well as chemical composition assumed in models were used to derive the new expressions for ionization-correction factors that were used to redetermine the chemical compositions of 88 H II regions in blue compact dwarf galaxies. It must be noticed that we used for this propose the ionic abundances obtained by Izotov et al. (2007). In result the primordial helium abundance and its enrichment during stellar chemical evolution of matter were determined.

scholarly journals Inhomogeneous H II Regions and the Helium Abundance

2000 ◽  
Vol 198 ◽  
pp. 188-193 ◽  
Author(s):  
S. M. Viegas ◽  
R. Gruenwald
Keyword(s):  
Correction Factor ◽  
H Ii Regions ◽  
Helium Abundance ◽  
Stellar Clusters ◽  
Low Metallicity ◽  
Primordial Helium

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.

scholarly journals Measurement of the primordial helium abundance from the intergalactic medium

2018 ◽  
Vol 2 (12) ◽  
pp. 957-961 ◽  
Author(s):  
Ryan J. Cooke ◽  
Michele Fumagalli
Keyword(s):  
Intergalactic Medium ◽  
Helium Abundance ◽  
Primordial Helium

Very Metal-Poor Galaxies and the Primordial Helium Abundance

1994 ◽  
pp. 182-191
Author(s):  
Elena Terlevich ◽  
Evan Skillman ◽  
Roberto Terlevich
Keyword(s):  
Helium Abundance ◽  
Primordial Helium

scholarly journals Determination of the Primordial Helium Abundance Based on NGC 346, an H ii Region of the Small Magellanic Cloud

2019 ◽  
Vol 876 (2) ◽  
pp. 98 ◽  
Author(s):  
Mabel Valerdi ◽  
Antonio Peimbert ◽  
Manuel Peimbert ◽  
Andrés Sixtos
Keyword(s):  
Magellanic Cloud ◽  
Helium Abundance ◽  
Small Magellanic Cloud ◽  
H Ii Region ◽  
Primordial Helium

Spectrophotometry of 12 metal-poor galaxies - Implications for the primordial helium abundance

1983 ◽  
Vol 273 ◽  
pp. 81 ◽  
Author(s):  
D. Kunth ◽  
W. L. W. Sargent
Keyword(s):  
Helium Abundance ◽  
Primordial Helium

On determining the primordial helium abundance from the spectra of H II galaxies

1992 ◽  
Vol 401 ◽  
pp. 157 ◽  
Author(s):  
Alison Campbell
Keyword(s):  
Helium Abundance ◽  
Primordial Helium

scholarly journals The primordial helium abundance from updated emissivities

2013 ◽  
Vol 2013 (11) ◽  
pp. 017-017 ◽  
Author(s):  
Erik Aver ◽  
Keith A Olive ◽  
R.L Porter ◽  
Evan D Skillman
Keyword(s):  
Helium Abundance ◽  
Primordial Helium
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