Del Zanna, G;
Storey, PJ;
(2022)
Helium line emissivities for nebular astrophysics.
Monthly Notices of the Royal Astronomical Society
, 513
(1)
pp. 1198-1209.
10.1093/mnras/stac800.
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Abstract
We present the results of several collisional-radiative models describing optically thin emissivities of the main lines in neutral helium formed by recombination, for a grid of electron temperatures and densities, typical of H II regions and planetary nebulae. Accurate emissivities are required for example to measure the helium abundance in nebulae and as a consequence its primordial value. We compare our results with those obtained by previous models, finding significant differences, well above the target accuracy of 1 per cent. We discuss in some detail our chosen set of atomic rates and the differences with those adopted by previous models. The main differences lie in the treatment of electron and proton collision rates and we discuss which transitions are least sensitive to the choice of these rates and therefore best suited to high-precision abundance determinations. We have focused our comparisons on the case B approximation where only He and He+ are considered, but also present results of full models including the bare nuclei, photoexcitation, and photoionization, and either black-body or observed illuminating spectrum in the case of the Orion nebula, to indicate which spectral lines are affected by opacity. For those transitions, accurate radiative transfer calculations should be performed. We provide tables of emissivities for all transitions within n ≤ 5 and all those between the n ≤ 5 and n′ ≤ 25 states, in the log Te (K) = 103.0(0.1)4.6 and log Ne (cm−3) = 102(0.5)6 ranges, and a FORTRAN code to interpolate to any Te, Ne within these ranges.
| Type: | Article |
|---|---|
| Title: | Helium line emissivities for nebular astrophysics |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1093/mnras/stac800 |
| Publisher version: | https://doi.org/10.1093/mnras/stac800 |
| Language: | English |
| Additional information: | © The Author(s) 2022. Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/) |
| Keywords: | atomic data, atomic processes, ISM: atoms, ISM: clouds, H II regions |
| UCL classification: | UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy UCL > Provost and Vice Provost Offices > UCL BEAMS UCL |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10149876 |
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