Improving circumbinary planet detections by fitting their binary's apsidal precession

Abstract

Apsidal precession in stellar binaries is the main non-Keplerian dynamical effect impacting the radial-velocities of a binary star system. Its presence can notably hide the presence of orbiting circumbinary planets because many fitting algorithms assume perfectly Keplerian motion. To first order, apsidal precession ($\dot{\omega }$) can be accounted for by adding a linear term to the usual Keplerian model. We include apsidal precession in the kima package, an orbital fitter designed to detect and characterise planets from radial velocity data. In this paper, we detail this and other additions to kima that improve fitting for stellar binaries and circumbinary planets including corrections from general relativity. We then demonstrate that fitting for $\dot{\omega }$ can improve the detection sensitivity to circumbinary exoplanets by up to an order of magnitude in some circumstances, particularly in the case of multi-planetary systems. In addition, we apply the algorithm to several real systems, producing a new measurement of aspidal precession in KOI-126 (a tight triple system), and a detection of $\dot{\omega }$ in the Kepler-16 circumbinary system. Although apsidal precession is detected for Kepler-16, it does not have a large effect on the detection limit or the planetary parameters. We also derive an expression for the precession an outer planet would induce on the inner binary and compare the value this predicts with the one we detect.

10 pages, 5 figures Re-submitted to MNRAS after reviewer comments

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• BEBOP VII. SOPHIE discovery of BEBOP-3b, a circumbinary giant planet on an eccentric orbit
• DMPP-4: Candidate sub-Neptune mass planets orbiting a naked-eye star
• Advancing accuracy in age determinations of old-disk stars using an oscillating red giant in an eclipsing binary
• Two neighbours of the ultra-short-period Earth-sized planet K2-157 b in the warm Neptunian savanna
• Modeling Apsidal Motion in Eclipsing Binaries using ELC
• Yuti: A General-purpose Transit Simulator for Arbitrary Shaped Objects Orbiting Stars
• GJ 9404 b: a confirmed eccentric planet, and not a candidate
• Inferring planet occurrence rates from radial velocities