Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992apj...401..157c&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 401, no. 1, p. 157-167.
Astronomy and Astrophysics
Astrophysics
22
Abundance, Cosmochemistry, H Ii Regions, Helium, Astronomical Models, Dwarf Galaxies, Interstellar Matter, Least Squares Method, Oxygen, Spectrum Analysis
Scientific paper
A data set of 53 H II galaxies and giant H II regions whose observed abundances have reliable formal uncertainties reveals that the O/H-He/H relation used to determine the primordial helium abundance (PBA) has a highly significant physical dispersion. Consideration of possible sources of scatter indicates that it is almost certainly one-sided, i.e., upward from a minimum value of He/H at each O/H. The presence of an asymmetric dispersion casts doubt on values of PBA obtained by extrapolating ridge-line fits to the O/H-He/H relation. The loss of oxygen in SN explosions will lead naturally to a positive dispersion in He/H. The observed dispersions in He/H can be explained by chemical evolution models in which 0-95 percent of the newly synthesized oxygen is lost. It is concluded that in H II galaxies and giant H II regions PBA can be reliably determined only by fitting to the lower envelope of the O/H-He/H relation.
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