A new evolutionary channel for Type Ia supernovae

ABSTRACT We show that long–period dwarf novae offer a promising route for making Type Iasupernovae. For typical dwarf nova duty cycles d ∼ 0.1 − 0.01, mass is accreted bythe white dwarf mainly during dwarf nova outbursts at rates allowing steady nuclearburning of most of the accreted matter. Mass gains up to ∼ 0.4M ⊙ are possible in thisway. Although these are too small to allow a 0.7M ⊙ WD to reach the Chandrasekharmass, 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 fromsupersoft binaries. A further advantage of this picture is that the supernova alwaysoccurs in a binary of small secondary/primary mass ratio, with the secondary havingverylittle remaining hydrogen.Both features greatlyreduce the possibility of hydrogencontamination of the supernova ejecta.Key words: accretion, accretion discs – binaries: general – X–rays: binaries – stars:dwarf novae – supernovae: general – galaxies: stellar content – cosmology: distancescale

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