H-, He-like recombination spectra -- V: On the dependence of the simulated line intensities on the number of electronic levels of the atoms

Abstract

This paper presents a study of the dependence of the simulated intensities of recombination lines from hydrogen and helium atoms on the number of $n\ell$-resolved principal quantum numbers included in the calculations. We simulate hydrogen and helium emitting astrophysical plasmas using the code Cloudy and show that, if not enough $n\ell$-resolved levels are included, recombination line intensities can be predicted with significant errors than can be more than 30\% for H~I IR lines and 10\% for He~I optical lines ($\sim$20\% for He~I IR recombination lines) at densities $\sim1\text{cm}^{-3}$, comparable to interstellar medium. This can have consequences in several spectroscopic studies where high accuracy is required, such as primordial helium abundance determination. Our results indicate that the minimum number of resolved levels included in the simulated hydrogen and helium ions of our spectral emission models should be adjusted to the specific lines to be predicted, as well as to the temperature and density conditions of the simulated plasma.