The resonance lines of sodium and potassium in brown dwarf spectra

Accurate pressure broadened line profiles of alkali resonance doublets are needed for the modelling of atmospheres of cool stars and for generating their synthetic spectra in the region 400 - 900 nm. When the lines utterly dominate their region of the spectrum, it becomes important to represent the profiles accurately over the whole range from the line centre to the far line wings. In this paper we examine the theories of spectral line shapes that have been used and carry out new calculations of the line shapes for the resonance lines of sodium and potassium broadened by helium.