Alkali 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 effects of dust in brown dwarf atmospheres. We report results for the Lorentzian profiles of the Na I and K I doublets broadened by helium perturbers for temperatures up to 3000 K. They have been obtained from a fully quantum-mechanical close-coupling description of the colliding atoms, the Baranger theory of line shapes and new ab initio potentials for the alkali-rare gas interaction