Recent work on the line shapes for the spectra of cool stars

Abstract

Accurate pressure broadened profiles of alkali resonance doublets perturbed by helium are needed for modelling of the atmospheres of late M, L and T type brown dwarfs for temperatures up to 3000 K. Previous fully quantum-mechanical calculations of line widths and shifts are extended to consider the line-wing profiles where impact theory is no longer valid. Results are presented for the Lorentzian line widths of the lithium, sodium and potassium resonance lines calculated using both impact and one-perturber theory. Excellent agreement between these two approximations is obtained, demonstrating that quantum-mechanical calculations of the line profiles can be made that are accurate over the whole range of frequencies from the line centre to the line wings.