Caustic Structures and Detectability of Circumbinary Planets in Microlensing

Abstract

Recent discoveries of circumbinary planets in Kepler data show that there is a viable channel of planet formation around binary main sequence stars. Motivated by these discoveries, we have investigated the caustic structures and detectability of circumbinary planets in microlensing events. We have produced a suite of animations of caustics as a function of the projected separation and angle of the binary host to efficiently explore caustic structures over the entire circumbinary parameter space. Aided by these animations, we have derived a semi-empirical analytic expression for the location of planetary caustics, which are displaced in circumbinary lenses relative to those of planets with a single host. We have used this expression to show that the dominant source of caustic motion will be due to the planet's orbital motion and not that of the binary star. Finally, we estimate the fraction of circumbinary microlensing events that are recognizable as such to be significant (5-50 percent) for binary projected separations in the range 0.1-0.5 in units of Einstein radii.

15 pages, 1 table, 18 figures. Accepted for publication in ApJ

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• Predictions of the WFIRST Microlensing Survey I: Bound Planet Detection Rates
• The First Circumbinary Planet Found by Microlensing: OGLE-2007-BLG-349L(AB)c
• Modeling microlensing events with MulensModel
• Listening to the gravitational wave sound of circumbinary exoplanets
• OGLE-2016-BLG-0613LABb: A Microlensing Planet in a Binary System
• Triple-lens Gravitational Microlensing: Critical Curves for Arbitrary Spatial Configuration
• OGLE-2019-BLG-1470LABc: Another Microlensing Giant Planet in a Binary System?
• Running The Gauntlet -- Survival of Small Circumbinary Planets Migrating Through Destabilising Resonances
• Sculpting the circumbinary planet size distribution through resonant interactions with companion planets
• Orbital dynamics of two circumbinary planets around misaligned eccentric binaries
• Detections of Planets in Binaries Through the Channel of Chang-Refsdal Gravitational Lensing Events
• Simulations of Triple Microlensing Events I: Detectability of a scaled Sun-Jupiter-Saturn System