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

F. Guzmán, N. R. Badnell, R. J. R. Williams, P.A.M. van Hoof, M. Chatzikos, G. J. Ferland

Research output: Contribution to journalArticle

9 Citations (Scopus)

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.
LanguageEnglish
Pages312-320
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Volume464
Issue number1
Early online date12 Sep 2016
DOIs
Publication statusPublished - 1 Jan 2017

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recombination
collision
emissivity
collisions
coefficients
energy
H II regions
prediction
predictions
nuclear fusion
helium
approximation
simulation
atoms
rate
calculation
code

Keywords

  • atomic data
  • ISM abundances
  • H II regions
  • cosmology observations
  • primordial nucleosynthesis
  • primordial abundances
  • helium
  • line emissivities
  • collisional rate coefficients
  • energy separation
  • energy-degenerate collisional theories
  • Bethe approximation
  • Rydberg states

Cite this

Guzmán, F. ; Badnell, N. R. ; Williams, R. J. R. ; van Hoof, P.A.M. ; Chatzikos, M. ; Ferland, G. J. / H, He-like recombination spectra - II ι-changing collisions for He Rydberg states. In: Monthly Notices of the Royal Astronomical Society. 2017 ; Vol. 464, No. 1. pp. 312-320.
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H, He-like recombination spectra - II ι-changing collisions for He Rydberg states. / Guzmán, F.; Badnell, N. R.; Williams, R. J. R.; van Hoof, P.A.M.; Chatzikos, M. ; Ferland, G. J.

In: Monthly Notices of the Royal Astronomical Society, Vol. 464, No. 1, 01.01.2017, p. 312-320.

Research output: Contribution to journalArticle

TY - JOUR

T1 - H, He-like recombination spectra - II ι-changing collisions for He Rydberg states

AU - Guzmán, F.

AU - Badnell, N. R.

AU - Williams, R. J. R.

AU - van Hoof, P.A.M.

AU - Chatzikos, M.

AU - Ferland, G. J.

N1 - 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.

PY - 2017/1/1

Y1 - 2017/1/1

N2 - 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.

AB - 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.

KW - atomic data

KW - ISM abundances

KW - H II regions

KW - cosmology observations

KW - primordial nucleosynthesis

KW - primordial abundances

KW - helium

KW - line emissivities

KW - collisional rate coefficients

KW - energy separation

KW - energy-degenerate collisional theories

KW - Bethe approximation

KW - Rydberg states

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T2 - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

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ER -