Improved He I Emissivities in the Case B Approximation

TL;DR

This paper updates helium I emissivity calculations using new, accurate photoionisation cross-sections, improving the reliability of spectral modeling across a wide range of temperatures and densities.

Contribution

It introduces a comprehensive set of ab initio photoionisation cross-sections that enhance the accuracy and consistency of He I emissivity calculations compared to previous methods.

Findings

New effective recombination coefficients compared favorably with prior work.

Updated emissivities show improved consistency with bound-bound transition probabilities.

Results cover a broad range of temperatures and densities, enhancing modeling accuracy.

Abstract

We update our prior work on the case B collisional-recombination spectrum of He I to incorporate \textit{ab initio} photoionisation cross-sections. This large set of accurate, self-consistent cross-sections represents a significant improvement in He I emissivity calculations because it largely obviates the piecemeal nature that has marked all modern works. A second, more recent set of \textit{ab initio} cross-sections is also available, but we show that those are less consistent with bound-bound transition probabilities than our adopted set. We compare our new effective recombination coefficients with our prior work and our new emissivities with those by other researchers, and we conclude with brief remarks on the effects of the present work on the He I error budget. Our calculations cover temperatures $5000 \le T_e \le 25000$ K and densities $10^1 \le n_e \le 10^{14}$ cm$^{-3}$. Full results are available online.