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 similar to 0.1 to a few times 10(-3) mass is accreted by the white dwarf (WD) mainly during dwarf nova outbursts at rates allowing steady nuclear burning of most of the accreted matter. Mass gains of up to similar to0.4 M(circle dot) are possible in this way. Although these are too small to allow a 0.7-M(circle dot) WD to reach the Chandrasekhar mass, they are sufficient if the WD grew to greater than or similar to1 M(circle dot) in a previous episode of thermal time-scale 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.