THERMAL TIMESCALE MASS TRANSFER AND THE EVOLUTION OF WHITE DWARF BINARIES

摘要

The evolution of binaries consisting of evolved main-sequence stars (1 < M_d/solar mass < 3.5) with white dwarf companions (0.7 < M_(wd)/solar mass < 1.2) is investigated through the thermal mass-transfer phase. Taking into account the stabilizing effect of a strong, optically thick wind from the accreting white dwarf surface, we have explored the formation of several evolutionary groups of systems for progenitors with initial orbital periods of 1 and 2 days. The numerical results show that CO white dwarfs can accrete sufficient mass to evolve to a Type Ia supernova, and ONeMg white dwarfs can be built up to undergo accretion-induced collapse for donors more massive than about 2 solar mass. For donors less massive than ～2 solar mass, the system can evolve to form an He and CO or ONeMg white dwarf pair. In addition, sufficient helium can be accumulated (～0.1 solar mass) in systems characterized by 1.6 approx< M_d/solar mass approx<1.9 and 0.8 approx< M_(wd)/solar mass approx<1 such that sub-Chandrasekhar-mass models for Type Ia super-novae, involving off-center helium ignition, are possible for progenitor systems evolving via the Case A mass-transfer phase. For systems characterized by mass ratios approx>3, the system likely merges as a result of the occurrence of a delayed dynamical mass-transfer instability. We develop a semianalytical model to delineate these phases that can be easily incorporated in population synthesis studies of these systems.