Orbital evolution in binary systems with giant stars

Zhuo Chen, Eric G. Blackman, Jason Nordhaus, Adam Frank, Jonathan Carroll-Nellenback

Published 2017-05-04Version 1

Using 3D radiation-hydrodynamic simulations and analytic theory, we analyze the orbital evolution of asymptotic-giant-branch (AGB) binary systems for various initial orbital separations and mass ratios, and thus different initial accretion modes. We present a convenient analytic framework to calculate the rate of orbital period change using input from simulations. We find that the angular momentum carried away by the L2 Lagrange point mass loss can effectively shrink the orbit when accretion occurs via wind-Roche-lobe overflow. This is in contrast to the large mass loss in Bondi-Hoyle accretion systems which acts to enlarge the orbit. We find that orbital period decay in AGB binary systems is faster when one accounts for the nonlinear evolution of the accretion mode as the binary starts to tighten. This can increase the fraction of binaries that result in common envelope, luminous red novae, Type Ia supernovae and planetary nebulae with tight central binaries. The results have implications for the probability and properties of planets orbiting closely around white dwarfs.