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R. P. Bauman, K. B. MacAdam, G. J. Ferland (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 initial results of a reinvestigation of the helium and hydrogen recombination processes. Our work builds on previous studies by improving the physical treatment of radiative recombination and subsequent cascades. Our treatment explicitly includes fine structure and singlet-triplet mixing in the helium transition rates. We base our transition rates on the results of Drake( Atomic, Molecular, & Optical Physics Handbook, AIP Press, Woodbury New York, 1996 ). Previous studies of helium recombination were largely based on variational, hydrogenic or Coulomb approximation calculations that did not include magnetic and relativistic interactions, thus entailing an unknown degree of inaccuracy. Comparisons with previous calculations are presented along with an assessment of the remaining major uncertainties. This work was supported in part by NSF and NASA.
The author(s) of this abstract have provided an email address for comments about the abstract: bauman@pa.uky.edu