The chemical pollution of the secondary of a cataclysmicvariable

We study the chemical evolution of population I and population II secondaries in cata-clysmic variables (CVs) assuming that during nova explosions a part of the high metal-licity nova ejecta is intercepted by the secondary and mixed into its convective envelope. We derive analytic expressions for the chemical composition of the secondary's envelope as a function of the chemical composition of the nova ejecta X i;ej and the secondary's cross section. For Pop I CVs we nd that the increase of the secondary's metallicity is comparable to its initial metallicity only if is larger by an order of magnitude than the geometrical cross section. A signiicant accumulation is therefore possible only in those species which are highly overabundant in the nova ejecta. Because the changes in the abundances of even those species depend strongly on the poorly known cross section , the predictive power of our model is weak for Pop I CVs as long as is not well determined. In case of Pop II CVs the accumulation of heavy elements by this process dominates over the initial metallicity of the secondary even for values of which are smaller by an order of magnitude than the geometrical cross section. Thus, within a short time after turn{on of mass transfer, the relative metal abundances in the secondary's envelope reeect those in the nova ejecta. This is nearly independent of the cross section .