On the Formation of Helium Double Degenerate Stars and Pre-Cataclysmic Variables

摘要: The evolution of low-mass (M \ 2.5 binaries through the common envelope phase has been M _ ) studied for systems in which one member is on its —rst ascent red giant branch. Three-dimensional hydrodynamical simulations have carried out a range masses (1¨2 with degen- erate helium cores (0.28¨0.45 and companions (0.1¨0.45 initial orbital periods ranging from D15 to 1000 days. results suggest that these binary can survive provided degenerate core more massive than about 0.2¨0.25 mass progenitor Speci—c applications are made observed double (2 . systems, precataclysmic variables, subdwarf B stars order place constraints evolving phase. For short-period it found evolutionary scenarios involving two phases not likely scenario an Algol-like transfer fol- lowed by viable, suggesting —rst-formed white dwarf often reheated nuclear burning surface. A formation mechanism eclipsing main-sequence also described. Subject headings: binaries: closecircumstellar matterhydrodynamics ¨ novae, cataclysmic variablesstars: evolutionstars: interiors