Improved He I Emissivities in the Case B Approximation

R.L. Porter (1), G.J. Ferland (2), P.J. Storey (3), M.J. Detisch (2) ((1)Department of Physics and Astronomy and Center for Simulational Physics, University of Georgia, Athens, GA 30602, USA;(2)Dept. of Physics & Astronomy, University of Kentucky, Lexington, KY 40506, USA; (3)Dept. of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK)

We update our prior work on the case B collisional-recombination spectrum of He I to incorporate ab initio photoionisation cross-sections. This large set of accurate, self-consistent cross-sections represents a significant improvement in He I emissivity calculations because it largely obviates the piecemeal nature that has marked all modern works. A second, more recent set of ab initio cross-sections is also available, but we show that those are less consistent with bound-bound transition probabilities than our adopted set. We compare our new effective recombination coefficients with our prior work and our new emissivities with those by other researchers, and we conclude with brief remarks on the effects of the present work on the He I error budget. Our calculations cover temperatures 5000 ≤ Te ≤ 25000 K and densities 10^1 ≤ ne ≤ 10^{14} cm^{-3}. Full results are available online.

See complete preprint ==> http://arxiv.org/abs/1206.4115

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