On the abundance of circumbinary planets

Abstract

We present here the first observationally based determination of the rate of occurrence of circumbinary planets. This is derived from the publicly available Kepler data, using an automated search algorithm and debiasing process to produce occurrence rates implied by the seven systems already known. These rates depend critically on the planetary inclination distribution: if circumbinary planets are preferentially coplanar with their host binaries, as has been suggested, then the rate of occurrence of planets with R p > 6R ⊕ orbiting with P p < 300 d is 10.0 +18 −6.5 % (95% confidence limits), higher than but consistent with single star rates. If on the other hand the underlying planetary inclination distribution is isotropic, then this occurrence rate rises dramatically, to give a lower limit of 47%. This implies that formation and subsequent dynamical evolution in circumbinary disks must either lead to largely coplanar planets, or proceed with significantly greater ease than in circumstellar disks. As a result of this investigation we also show that giant planets (>10R ⊕ ) are significantly less common in circumbinary orbits than their smaller siblings, and confirm that the proposed shortfall of circumbinary planets orbiting the shorter period binaries in the Kepler sample is a real effect.

No circumbinary planets transiting the tightestKeplerbinaries – a possible fingerprint of a third star

“…In this paper we show how this absence of planets may be a natural consequence of close binary formation, formalising an explanation that was briefly proposed by Welsh et al (2014a), Armstrong et al (2014), Martin & Triaud (2014) and Winn & Fabrycky (2014). A popular theory proposes that most very close binaries ( 7 d) are initially formed at wider separations.…”

“…The red dashed vertical lines indicate the binary periods around which planets have been found, of which the shortest is P in = 7.4 d (Kepler-47). Armstrong et al (2014) analysed the Kepler lightcurves using an automated search algorithm and debiasing process, and came to 1 The latest version of the catalog can be found online at http://keplerebs.villanova.edu, maintained by Prsa et al at Villanova University. 2 The planet hunters consortium at http://www.planethunters.org/.…”

Planets transiting non-eclipsing binaries

“…Recently, Armstrong et al (2014), who used an independent method of analysing the Kepler lightcurves to constrain the abundance, found a compatible estimate. It will also be interesting to see how our value compares with future studies.…”

Single transit candidates from K2: detection and period estimation

“…The fit for each was iterated 20 times, with points >5σ from the best-fitting excluded each time. This method is further explained in Armstrong et al (2014). The resulting polynomial fit was then applied to the central 4-h windows, thus avoiding artificially reducing transit depths.…”