We present a set of full evolutionary sequences for white dwarfs with hydrogen-deficient atmospheres .
We take into account the evolutionary history of the progenitor stars , all the relevant energy sources involved in the cooling , element diffusion in the very outer layers , and outer boundary conditions provided by new and detailed non-gray white dwarf model atmospheres for pure helium composition .
These model atmospheres are based on the most up-to-date physical inputs .
Our calculations extend down to very low effective temperatures , of \sim 2 500 K , provide a homogeneous set of evolutionary cooling tracks that are appropriate for mass and age determinations of old hydrogen-deficient white dwarfs , and represent a clear improvement over previous efforts , which were computed using gray atmospheres .