A comparison of laboratory spectra with a new theoretical study of potassium resonance lines perturbed by helium

The optical spectra of L- and T-type dwarfs exhibit a continuum dominated by the far wings of the absorption profiles of the Na 3s-3p and K 4s-4p doublets perturbed by molecular hydrogen and helium. We examine the K resonance line wing and core with a unified line profile theory and compare to laboratory experiments and observations of the cool brown dwarf ϵ  Indi  Ba,b .