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Register a new userDistinguishing Polar and Co-planar Circumbinary Exoplanets by Eclipsing Timing Variations
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Circumbinary Planets (CBPs) can be misaligned with their host binary stars. Orbital dynamics, simulations, and recent observations of proto-planetary disks all suggest that the planet can stably orbit in a plane perpendicular to that of an eccentric host binary star (i.e., a polar orbit). No solid claim of detection of such a configuration has been made; the nine systems detected by the transit technique are nearly coplanar, but their discovery is also biased towards that configuration. Here, we develop Eclipse Timing Variations (ETVs) as a method to detect misaligned CBPs. We find that since apsidal motion (periastron precession) of the host binary is prograde for a coplanar planet and retrograde for a polar planet, the mean eclipse period of primary and secondary eclipses differ in a way that distinguishes those configurations. Secondly, the Eclipse Duration Variations (EDVs) vary in a way that can confirm that inference, over and against a polar model. Thirdly, the relative phasing of primary and secondary ETVs on the planets orbital timescale also distinguishes the two configurations, which we explain analytically and quantify through a grid of numerical models. We apply these methods to Kepler-34, a transiting planet known to be nearly coplanar by detailed photodynamic modeling. In this system, we find that the binary eclipse times alone suffice to distinguish these orbital configurations, using the effects introduced here. Our work provides a tool for discovering potential polar CBPs, or misaligned CBPs of milder inclinations, from the existing ETV dataset of the Kepler, as well as future observations by TESS or PLATO.
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We present an efficient analytical method to predict the maximum transit timing variations of a circumbinary exoplanet, given some basic parameters of the host binary. We derive an analytical model giving limits on the potential location of transits for coplanar planets orbiting eclipsing binaries, then test it against numerical N-body simulations of a distribution of binaries and planets. We also show the application of the analytic model to Kepler-16b, -34b and -35b. The resulting method is fast, efficient and is accurate to approximately 1% in predicting limits on possible times of transits over a three-year observing campaign. The model can easily be used to, for example, place constraints on transit timing while performing circumbinary planet searches on large datasets. It is adaptable to use in situations where some or many of the planet and binary parameters are unknown.
The Kepler Mission is monitoring the brightness of ~150,000 stars searching for evidence of planetary transits. As part of the Hunt for Exomoons with Kepler (HEK) project, we report a planetary system with two confirmed planets and one candidate planet discovered using the publicly available data for KOI-872. Planet b transits the host star with a period P_b=33.6d and exhibits large transit timing variations indicative of a perturber. Dynamical modeling uniquely detects an outer nontransiting planet c near the 5:3 resonance (P_c=57.0d) of mass 0.37 times that of Jupiter. Transits of a third planetary candidate are also found: a 1.7-Earth radius super-Earth with a 6.8d period. Our analysis indicates a system with nearly coplanar and circular orbits, reminiscent of the orderly arrangement within the solar system.
The hot-Jupiter WASP-10b was reported by Maciejewski et al. (2011a,b) to show transit timing variations (TTV) with an amplitude of ~ 3.5 minutes. These authors proposed that the observed TTVs were caused by a 0.1 MJup perturbing companion with an orbital period of ~ 5.23 d, and hence, close to the outer 5:3 mean motion resonance with WASP-10b. To test this scenario, we present eight new transit light curves of WASP-10b obtained with the Faulkes Telescope North and the Liverpool Telescope. The new light curves, together with 22 previously published ones, were modelled with a Markov-Chain Monte-Carlo transit fitting code. (...) Our homogeneously derived transit times do not support the previous claimed TTV signal, which was strongly dependent on 2 previously published transits that have been incorrectly normalised. Nevertheless, a linear ephemeris is not a statistically good fit to the transit times of WASP-10b. We show that the observed transit time variations are due to spot occultation features or systematics. We discuss and exemplify the effects of occultation spot features in the measured transit times and show that despite spot occultation during egress and ingress being difficult to distinguish in the transit light curves, they have a significant effect in the measured transit times. We conclude that if we account for spot features, the transit times of WASP-10 are consistent with a linear ephemeris with the exception of one transit (epoch 143) which is a partial transit. Therefore, there is currently no evidence for the existence of a companion to WASP-10b. Our results support the lack of TTVs of hot-Jupiters reported for the Kepler sample.
We explore the prospects for the detection of giant circumbinary exoplanets and brown dwarfs (BDs) orbiting Galactic double white dwarfs binaries (DWDs) with the Laser Interferometer Space Antenna (LISA). By assuming an occurrence rate of 50%, motivated by white dwarf pollution observations, we built a Galactic synthetic population of P-type giant exoplanets and BDs orbiting DWDs. We carried this out by injecting different sub-stellar populations, with various mass and orbital separation characteristics, into the DWD population used in the LISA mission proposal. We then performed a Fisher matrix analysis to measure how many of these three-body systems show a periodic Doppler-shifted gravitational wave perturbation detectable by LISA. We report the number of circumbinary planets (CBPs) and (BDs) that can be detected by LISA for various combinations of mass and semi-major axis distributions. We identify pessimistic and optimistic scenarios corresponding, respectively, to 3 and 83 (14 and 2218) detections of CBPs (BDs), observed during the length of the nominal LISA mission. These detections are distributed all over the Galaxy following the underlying DWD distribution, and they are biased towards DWDs with higher LISA signal-to-noise ratio and shorter orbital period. Finally, we show that if LISA were to be extended for four more years, the number of systems detected will be more than doubled in both the optimistic and pessimistic scenarios. Our results present promising prospects for the detection of post-main sequence exoplanets and BDs, showing that gravitational waves can prove the existence of these populations over the totality of the Milky Way. Detections by LISA will deepen our knowledge on the life of exoplanets subsequent to the most extreme evolution phases of their hosts, clarifying whether new phases of planetary formation take place later in the life of the stars.
To date more than 3500 exoplanets have been discovered orbiting a large variety of stars. Due to the sensitivity limits of the currently used detection techniques, these planets populate zones restricted either to the solar neighbourhood or towards the Galactic bulge. This selection problem prevents us from unveiling the true Galactic planetary population and is not set to change for the next two decades. Here we present a new detection method that overcomes this issue and that will allow us to detect gas giant exoplanets using gravitational wave astronomy. We show that the Laser Interferometer Space Antenna (LISA) mission can characterise hundreds of new circumbinary exoplanets orbiting white dwarf binaries everywhere in our Galaxy - a population of exoplanets so far completely unprobed - as well as detecting extragalactic bound exoplanets in the Magellanic Clouds. Such a method is not limited by stellar activity and, in extremely favourable cases, will allow LISA to detect super-Earths down to 10 Earth masses.
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