Asymmetrical shape of the Near-Infrared K 4p-5s doublet perturbed by He and H2

Abstract

The goal of this paper is to provide an exhaustive study of the K 4p-5s doublet at 1.243/1.252~$\mu$m perturbed by He and H${}_2$ in physical conditions of brown dwarfs. This work is applicable to analysis of the ESO SupJup Survey's J-band spectra such as for Luhman~16. Line profiles of this doublet computed within a unified line-shape theory exhibit a blue asymmetrical behavior. This effect is of increasing importance with He and H2 density, and as a result, the full treatment of the infrared K doublet reveals strong effects on its opacity outside the impact approximation. For a He and H2 perturber density larger than $10^{19}$~cm${}^{-3}$ (0.4 bar) the impact approximation breaks down and is not applicable to calculate the shape of the line profiles and their line core parameters.