Effects of a New Triple-α Reaction Rate on the Helium Ignition of Accreting White Dwarfs

The effects of a new triple-a reaction rate on the ignition of carbon-oxygen white dwarfs accreting helium in a binary system have been investigated. The ignition points determine the properties of a thermonuclear explosion of a Type Ia supernova. We examine the cases of different accretion rates of helium and different initial masses of the white dwarf, which was studied in detail by Nornoto [K. Nomoto, Astrophys. J. 253 (1982), 798]. We find that for all cases from slow to intermediate accretion rates, nuclear burnings are ignited at the helium layers. As a consequence, carbon deflagration would be triggered for lower accretion rate than dM/dt similar or equal to 4 x 10(-8) M(circle dot) yr(-1) which has been believed to be the lower limit of the accretion rate for the deflagration supernova. Furthermore, off-center helium detonation should result for intermediate and slow accretion rates, and the region of carbon deflagration for slow accretion rates disappears.