### Abstract

Language | English |
---|---|

Pages | 312-320 |

Number of pages | 9 |

Journal | Monthly Notices of the Royal Astronomical Society |

Volume | 464 |

Issue number | 1 |

Early online date | 12 Sep 2016 |

DOIs | |

Publication status | Published - 1 Jan 2017 |

### Fingerprint

### 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

*Monthly Notices of the Royal Astronomical Society*,

*464*(1), 312-320. https://doi.org/10.1093/mnras/stw2304

}

*Monthly Notices of the Royal Astronomical Society*, vol. 464, no. 1, pp. 312-320. https://doi.org/10.1093/mnras/stw2304

**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.

Research output: Contribution to journal › Article

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

UR - https://mnras.oxfordjournals.org/

U2 - 10.1093/mnras/stw2304

DO - 10.1093/mnras/stw2304

M3 - Article

VL - 464

SP - 312

EP - 320

JO - Monthly Notices of the Royal Astronomical Society

T2 - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 1

ER -