Dynamic Mass Exchange in Doubly Degenerate Binaries. II. The Importance of Nuclear Energy Release

Abstract

The hypothesis that Type I supernova explosions originate in binary stars, in which the secondary overflows its Roche lobe and causes a white dwarf primary to pass a critical threshold for dynamical collapse, has gained in popularity over the last decade and a half (Truran and Cameron 1971; Whelan and Iben 1973; Wheeler 1982). During this period attention has also focussed on double-degenerate binary precursors of such systems, in which gravitational radiation of orbital angular momentum causes two white dwarf stars to spiral slowly together until the less massive of the stars begins to overflow its Roche lobe (Tutukov and Yungelson 1979; Webbink 1979; Iben and Tutukov 1984; Paczyński 1985). Cameron and Iben (1986) discussed the stability of such systems as the threshold of Roche lobe overflow was approached and for low mass ratios in which gravitational radiation can maintain a low rate of such overflow. Benz, Bowers, Cameron, and Press (1988, hereafter BBCP) computed the actual merging of a binary system composed of a 1.2M© primary and a 0.9M© secondary using a fully three-dimensional SPH code. Their simulation did not include the effect of nuclear energy release despite the fact that the temperature in the accretion shock reached the carbon ignition threshold, and therefore their conclusions about the structure of the merged object remained uncertain.