H, He-like recombination spectra - II ι-changing collisions for He Rydberg states

Guzmán, F. and Badnell, N. R. and Williams, R. J. R. and van Hoof, P.A.M. and Chatzikos, M. and Ferland, G. J. (2017) H, He-like recombination spectra - II ι-changing collisions for He Rydberg states. Monthly Notices of the Royal Astronomical Society, 464 (1). pp. 312-320. ISSN 0035-8711 (https://doi.org/10.1093/mnras/stw2304)

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Abstract

Cosmological models can be constrained by determining primordial abundances. Accurate predictions of the He I spectrum are needed to determine the primordial helium abundance to a precision of <1 per cent in order to constrain big bang nucleosynthesis models. Theoretical line emissivities at least this accurate are needed if this precision is to be achieved. In the first paper of this series, which focused on H I, we showed that differences in l-changing collisional rate coefficients predicted by three different theories can translate into 10 per cent changes in predictions for H I spectra. Here, we consider the more complicated case of He atoms, where low-l subshells are not energy degenerate. A criterion for deciding when the energy separation between l subshells is small enough to apply energy-degenerate collisional theories is given. Moreover, for certain conditions, the Bethe approximation originally proposed by Pengelly & Seaton is not sufficiently accurate. We introduce a simple modification of this theory which leads to rate coefficients which agree well with those obtained from pure quantal calculations using the approach of Vrinceanu et al. We show that the l-changing rate coefficients from the different theoretical approaches lead to differences of ∼10 per cent in He I emissivities in simulations of H II regions using spectral code CLOUDY.

ORCID iDs

Guzmán, F., Badnell, N. R. ORCID logoORCID: https://orcid.org/0000-0001-7418-7996, Williams, R. J. R., van Hoof, P.A.M., Chatzikos, M. and Ferland, G. J.;
  • Item type:Article
    ID code:58268
    Dates:
    Date
    Event
    1 January 2017
    Published
    12 September 2016
    Published Online
    9 September 2016
    Accepted
    Notes:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
    Subjects:Science > Physics
    Science > Astronomy
    Department:Faculty of Science > Physics
    Depositing user: Pure Administrator
    Date deposited:26 Oct 2016 09:41
    Last modified:11 Nov 2024 11:32
    Related URLs:
    URI:https://strathprints.strath.ac.uk/id/eprint/58268
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