Line shapes for the spectra of Brown Dwarfs

Highly accurate calculations of the central cores of pressure broadened alkali resonance doublets due to H2 and He perturbers are needed in order to estimate the eects of dust in brown dwarf atmospheres. We report results for Lorentzian alkali-line profiles broadened by helium perturbers. They are based on a fully quantum-mechanical close-coupling description of the colliding atoms, the Baranger theory of lineshapes and new ab initio potentials for the alkali-rare gas interaction