DOUBLE CORE EVOLUTION .8. THE SPIRAL-IN OF A MAIN-SEQUENCE STAR THROUGH THE ENVELOPE OF AN ASYMPTOTIC GIANT BRANCH COMPANION

A progenitor system for a cataclysmic variable binary consisting of a main-sequence star of 0.7 M(.) and a 3 M(.) asymptotic giant branch st ar (with a carbon-oxygen core of mass 0.7 M(.)) is evolved through the common envelope phase. The two-dimensional axisymmetric simulations s how that the entire common envelope is ejected without the two cores m erging together. It is demonstrated that the common envelope evolution terminates as a direct result of the spin-up to near corotation of ga s in the vicinity of the cores. The evolution of the common envelope h as been followed for sufficiently long times to show that the ejected matter remains confined to the equatorial plane at large distances (gr eater than or similar to 10(14) cm) from the double core. A new featur e in the ejected nebula is the appearance of multiple shock fronts whi ch develop as a result of nonuniform energy injection into the envelop e. Outward-moving pressure waves form which steepen into shocks as the density falls off in the envelope. The implications of the results fo r the origin of cataclysmic variables are discussed.