H, He-like recombination spectra I : l-changing collisions for hydrogen

Tools

Guzman, F. and Badnell, Nigel and Williams, R.J.R. and van Hoof, P.A.M. and Chatzikos, M. and Ferland, G.J. (2016) H, He-like recombination spectra I : l-changing collisions for hydrogen. Monthly Notices of the Royal Astronomical Society. ISSN 0035-8711 (In Press)

[thumbnail of Guzman-etal-MNRAS2016-H-He-like-recombination-spectra-I]
Preview
 Text. Filename: Guzman_etal_MNRAS2016_H_He_like_recombination_spectra_I.pdf
Accepted Author Manuscript
Download (230kB)| Preview

Abstract

Hydrogen and helium emission lines in nebulae form by radiative recombination. This is a simple process which, in principle, can be described to very high precision. Ratios of He I and H I emission lines can be used to measure the He+/H+ abundance ratio to the same precision as the recombination rate coefficients. This paper investigates the controversy over the correct theory to describe dipole l-changing collisions (nl → nl0 = l ±1) between energy-degenerate states within an n-shell. The work of Pengelly & Seaton (1964) has, for half-a-century, been considered the definitive study which “solved” the problem. Recent work by Vrinceanu et al. (2012) recommended the use of rate coefficients from a semi-classical approximation which are nearly an order of magnitude smaller than those of Pengelly & Seaton (1964), with the result that significantly higher densities are needed for the nl populations to come into local thermodynamic equilibrium. Here, we compare predicted H I emissivities from the two works and find widespread differences, of up to ≈ 10%. This far exceeds the 1% precision required to obtain the primordial He/H abundance ratio from observations so as to constrain Big Bang cosmologies. We recommend using the rate coefficients of Pengelly & Seaton (1964) for l-changing collisions, to describe the H recombination spectrum, based-on their quantum mechanical representation of the long-range dipole interaction.

ORCID iDs

Guzman, F., Badnell, Nigel 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:56192
    Dates:
    Date
    Event
    13 April 2016
    Published
    13 April 2016
    Accepted
    Notes:This is a pre-copyedited, author-produced PDF of an article accepted for publication in [insert journal title] following peer review. The version of record [insert complete citation information here] is available online at: xxxxxxx [insert URL that the author will receive upon publication here]
    Subjects:Science > Physics
    Department:Faculty of Science > Physics
    Depositing user: Pure Administrator
    Date deposited:19 Apr 2016 09:09
    Last modified:11 Nov 2024 11:24
    URI:https://strathprints.strath.ac.uk/id/eprint/56192
CORE (COnnecting REpositories)