Evolution of Accreting White Dwarfs to the Thermonuclear Runaway

Abstract

The two suggestions for the stars that explode as a supernova of type Ia are the single degenerate scenario and the double degenerate scenario. In the SD scenario, a white dwarf in a binary system accretes material from its companion and grows to the Chandrasekhar limit. Although there is no agreement on the progenitors, likely systems are the cataclysmic variables and symbiotic binaries which are close (or not so close) binary star systems which contain both a white dwarf (WD) primary and a larger cooler secondary star that typically fills its Roche lobe. The cooler star is losing mass through the inner Lagrangian point of the binary, and a fraction of this material is accreted by the WD. In this chapter, I investigate the consequences to the WD evolution of no mixing of accreted material with core material. The results are that once sufficient material has been accreted, thermonuclear burning is initiated and continues until a thermonuclear runaway occurs. The consequences of a thermonuclear runaway in solar composition material are that the WD ejects only a small fraction of the accreted material and, therefore, the WDs are growing in mass.