The chemical evolution of the secondary stars in close binary systems during nova outbursts

We present stellar evolutionary calculations of secondary stars in close binary systems. We include the effect of re-accretion of material ejected during the nova outbursts of the semi-detached phase of evolution. Our models give us the detailed composition of the secondary star throughout its whole evolution, since we use an extended nuclear reaction network. Using the data concerning the isotopic and element abundances of the surface of the secondary star, we show how the ratios of C-12/C-13, N-14/N-15 and O-16/(17O) and the abundances of C and N are affected by reaccretion of ejecta material. We suggest observational tests which, when compared with our results, will allow us to make predictions concerning the evolutionary state of the systems observed.