On the formation of oxygen-neon white dwarfs in close binary systems

The evolution of a star of initial mass 10 M-circle dot, and metallicity Z = 0.02 in a Close Binary System (CBS) is followed from its main sequence un til an ONe degenerate remnant forms. Restrictions have been made on the cha racteristics of the companion as well as on the initial orbital parameters in order to avoid the occurrence of reversal mass transfer before carbon is ignited in the core. The system undergoes three mass loss episodes. The fi rst and second ones are a consequence of a case B Roche lobe over ow. Durin g the third mass loss episode stellar winds may play a role comparable to, or even more important than Roche lobe over ow. In this paper, we extend th e previously existing calculations of stars of intermediate mass belonging to close binary systems by following carefully the carbon burning phase of the primary component. We also propose different possible outcomes for our scenario and discuss the relevance of our findings. In particular, our main result is that the resulting white dwarf component of mass 1.1 M-circle do t more likely has a core composed of oxygen and neon, surrounded by a mantl e of carbon-oxygen rich material. The average abundances of the oxygen-neon rich core are X(O-16) = 0.55, X(Ne-20) = 0.28, X(Na-23) = 0.06 and X(Mg-24 ) = 0.05. This result has important consequences for the Accretion Induced Collapse scenario. The average abundances of the carbon-oxygen rich mantle are X(O-16) = 0.55, and X(C-12) = 0.43. The existence of this mantle could also play a significant role in our understanding of cataclysmic variables.