The Formation of Massive White Dwarfs in Cataclysmic Binaries

Abstract

In contrast to the mass spectrum of single white dwarfs which has a single narrow peak at ~0.6 M⊙, the observed mass spectrum of white dwarfs of cataclysmic binaries (CB's) shows a rather uniform distribution of the masses in the range ~0.3 M⊙, to ~1.3 M⊙. The formation of CB's with white dwarfs of less than about 0.8 M⊙ can be understood as the result of a binary evolution according to low mass Case B or Case C with a subsequent spiraling-in in a common envelope. On the other hand the formation of massive white dwarfs of M ≲ 1 M⊙, can be explained as the result of a massive Case B mass transfer yielding a helium star which subsequently undergoes a second Case B mass transfer (so called Case BB evolution). The ultimate product of such an evolution is either a CO-white dwarf with a mass up to the Chandrasekhar limit or a neutron star. The formation of CB's via Case BB evolution requires the binary to undergo at least one, most probably two separate phases of spiraling-in in a common envelope.

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“…But in this case, the accreted material is mostly He, and the accretion rate can be very high, up to 10 -4 M ! y -1 (44). If the white dwarf is rapidly rotating or if mass is accreted faster than it loses angular momentum and thus spreads over the white dwarf, a He 'belt' will be accumulated.…”