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R.P. Bauman, G.J. Ferland, K.B. MacAdam (University of Kentucky)
The primordial abundance of helium and its subsequent production in stars are primarily determined from recombination lines in HII Regions. Accuracies better than a percent must be obtained to make definitive tests in cosmology. We report the results of a recalculation of the helium recombination process. Our work builds on previous calculations by improving the physical treatment of radiative recombination and subsequent cascades by explicitly including fine structure in the helium transition rates and energies. Transitions which are the result of singlet-triplet mixing are included in this work for the first time. We base our transition rates and energies on the results of Drake which include magnetic and relativistic interactions. Previous methodologies were largely based on variational, hydrogenic or Coulomb approximation calculations that did not include these interactions, thus entailing an unknown degree of inaccuracy. Comparisons with previous calculations are presented along with an assessment of the remaining major uncertainties. This project is supported by the NSF and NASA through grants AST 0071180 and NAG5-8212.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.