Long-term evolution of double white dwarf binaries accreting
through direct impact
- Vicky Kalogera,
- Kyle Kremer,
- Jeremy Sepinsky
Abstract
We calculate the long-term evolution of angular momentum in double
white dwarf binaries undergoing direct impact accretion over a
broad range of parameter space. We allow the rotation rate of both
components to vary, and account for the exchange angular
momentum between the spins of the white dwarfs and the orbit, while conserving the total angular momentum. We
include gravitational, tidal, and mass transfer effects in the orbital
evolution, and allow the Roche radius of the donor star to vary with
both the stellar mass and the rotation rate. We examine the long-term
stability of these systems, focusing in particular on those systems
that may be progenitors of AM CVn or Type Ia Supernovae. We find that our analysis yields an increase in the predicted number of stable systems compared to that in previous studies. Additionally, we find that by properly accounting for the effects of asynchronism between the donor and the orbit on the Roche-lobe size, we eliminate oscillations in the orbital parameters which are found in previous studies. Removing these oscilaltions can reduce the peak mass
transfer rate in some systems, keeping them from entering an unstable
mass transfer phase.