Multiple perturber effects in the far red wing of Lyman α line

A small fraction of the DA white dwarf are known to have rather low effective temperature. It is of considerable interest to determine line profiles in these extreme physical conditions. In such cool white dwarfs the perturber density is so high that the one perturber approximation breaks down and the collisional effects must be treated by using the autocorrelation formalism in order to take account the simultaneous collisions with more than one perturbing atom.