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The Degree of Alignment between Circumbinary Disks and Their Binary Hosts

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Abstract

  • All four circumbinary (CB) protoplanetary disks orbiting short-period (P disk that match, to within a few degrees, the sky-plane inclinations i of their stellar hosts. Although for these systems the true mutual inclinations θ between disk and binary cannot be directly measured because relative nodal angles are unknown, the near coincidence of i disk and i suggests that θ is small for these most compact of systems. We confirm this hypothesis using a hierarchical Bayesian analysis, showing that 68% of CB disks around short-period SB2s have θ suggests that θ is small for these most compact of systems. We confirm this hypothesis using a hierarchical Bayesian analysis, showing that 68% of CB disks around short-period SB2s have θ 5 days (where the nodal degeneracy can be broken via, e.g., binary astrometry), CB disks exhibit a wide range of mutual inclinations, from coplanar to polar. Many of these long-period binaries are eccentric, as their component stars are too far separated to be tidally circularized. We discuss how theories of binary formation and disk-binary gravitational interactions can accommodate all these observations.

Publication Date

  • 2019

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