Orbital evolution of close binary systems: comparing viscous and wind-driven circumbinary disc models
arxiv(2024)
摘要
Previous work has shown that interactions between a central binary system and
a circumbinary disc (CBD) can lead to the binary orbit either shrinking or
expanding, depending on the properties of the disc. In this work, we perform
two-dimensional hydrodynamical simulations of CBDs surrounding equal mass
binary systems that are on fixed circular orbits, using the Athena++ code in
Cartesian coordinates. Previous studies have focused on discs where viscosity
drives angular momentum transport. The aim of this work is to examine how the
evolution of a binary system changes when angular momentum is extracted from
the disc by a magnetised wind. In this proof-of-concept study, we mimic the
effects of a magnetic field by applying an external torque that results in a
prescribed radial mass flux through the disc. For three different values of the
radial mass flux, we compare how the binary system evolves when the disc is
either viscous or wind-driven. In all cases considered, our simulations predict
that the binary orbit should shrink faster by a factor of a few when surrounded
by a wind-driven circumbinary disc compared to a corresponding viscous
circumbinary disc. In-spiral timescales of ∼ 10^6-10^7yr are obtained
for circular binaries surrounded by CBDs with masses typical of protoplanetary
discs, indicating that significant orbital shrinkage can occur through
binary-disc interactions during Class I/II pre-main sequence phases.
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