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Astrophysics and Astronomy

University of Kentucky

Series

2016

Atomic data

Articles 1 - 2 of 2

Full-Text Articles in Physical Sciences and Mathematics

H-, He-Like Recombination Spectra ‒ Ii. L-Changing Collisions For He Rydberg States, Francisco Guzmán, N. R. Badnell, R. J. R. Williams, P. A. M. Van Hoof, Marios Chatzikos, Gary J. Ferland Sep 2016

H-, He-Like Recombination Spectra ‒ Ii. L-Changing Collisions For He Rydberg States, Francisco Guzmán, N. R. Badnell, R. J. R. Williams, P. A. M. Van Hoof, Marios Chatzikos, Gary J. Ferland

Physics and Astronomy Faculty Publications

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 ι, 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 ι 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 …

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H, He-Like Recombination Spectra – I. L-Changing Collisions For Hydrogen, Francisco Guzmán, N. R. Badnell, R. J. R. Williams, P. A. M. Van Hoof, Marios Chatzikos, Gary J. Ferland Apr 2016

H, He-Like Recombination Spectra – I. L-Changing Collisions For Hydrogen, Francisco Guzmán, N. R. Badnell, R. J. R. Williams, P. A. M. Van Hoof, Marios Chatzikos, Gary J. Ferland

Physics and Astronomy Faculty Publications

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 → nl′ = l ± 1) between energy-degenerate states within an n-shell. The work of Pengelly & Seaton has, for half-a-century, been considered the definitive …

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