Testing atomic collision theory with the two-photon continuum of astrophysical nebulae

Guzmán, F. and Badnell, N. R. and Chatzikos, M. and van Hoof, P. A. M. and Williams, R. J. R. and Ferland, G. J. (2017) Testing atomic collision theory with the two-photon continuum of astrophysical nebulae. Monthly Notices of the Royal Astronomical Society. ISSN 0035-8711

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    Abstract

    Accurate rates for energy-degenerate l-changing collisions are needed to determine cosmological abundances and recombination. There are now several competing theories for the treatment of this process, and it is not possible to test these experimentally. We show that the H i two-photon continuum produced by astrophysical nebulae is strongly affected by l-changing collisions. We perform an analysis of the different underlying atomic processes and simulate the recombination and two-photon spectrum of a nebula containing H and He. We provide an extended set of effective recombination coefficients and updated l-changing 2s − 2p transition rates using several competing theories. In principle, accurate astronomical observations could determine which theory is correct.