SN Ia Models by Coalescence of Two Carbon-Oxygen White Dwarfs

Abstract

White dwarf coalescence models for type Ia supernovae (SNe Ia) have been recently proposed [1,2] as an alternative to the standard scenario in which a white dwarf accretes hydrogen rich material from a companion star. The need for new models appeared after it was realized that it might be difficult to increase the white dwarf mass up to the Chandrasekhar limit by accretion, at least in a sufficiently large number of systems to account for the SN Ia rate in the Galaxy. Indeed, mass loss during hydrogen and helium flashes and off-center helium detonation considerably restrict the range of values of the accretion rate, white dwarf and companion masses for which central carbon ignition is possible. Another difficulty is the risk of contamination of the spectrum by stripped hydrogen from the companion. Even if a small window of parameters giving a SN Ia explosion may remain (the theoretical modelling of all the processes involved in the presupernova evolution is too uncertain to draw definite conclusions) the search for a new class of progenitors may turn to be more promising.