A New Evolutionary Channel for Type Ia Supernovae

We show that long–period dwarf novae offer a promising route for making Type Ia supernovae. For typical dwarf nova duty cycles d ∼ 0.1 − 0.01, mass is accreted by the white dwarf mainly during dwarf nova outbursts at rates allowing steady nuclear burning of most of the accreted matter. Mass gains up to ∼ 0.4M⊙ are possible in this way. Although these are too small to allow a 0.7M⊙ WD to reach the Chandrasekhar mass, they are sufficient if the WD grew to > ∼ 1M⊙ in a previous episode of thermal– timescale mass transfer, i.e. for those long–period dwarf novae which descend from supersoft binaries. A further advantage of this picture is that the supernova always occurs in a binary of small secondary/primary mass ratio, with the secondary having very little remaining hydrogen. Both features greatly reduce the possibility of hydrogen contamination of the supernova ejecta.