A search for multi-planet systems with TESS using a Bayesian N-body retrieval and machine learning

Abstract

Transiting exoplanets in multi-planet systems exhibit non-Keplerian orbits as a result of the gravitational influence from companions which can cause the times and durations of transits to vary. The amplitude and periodicity of the transit time variations (TTV) are characteristic of the perturbing planet's mass and orbit. The objects of interest (TOI) from the Transiting Exoplanet Survey Satellite (TESS) are analyzed in a uniform way to search for TTVs with sectors 1-3 of data. Due to the volume of targets in the TESS candidate list, artificial intelligence is used to expedite the search for planets by vetting non-transit signals prior to characterizing the light curve time series. The residuals of fitting a linear orbit ephemeris are used to search for transit timing variations. The significance of a perturbing planet is assessed by comparing the Bayesian evidence between a linear and non-linear ephemeris, which is based on an N-body simulation. Nested sampling is used to derive posterior distributions for the N-body ephemeris and in order to expedite convergence custom priors are designed using machine learning. A dual input, multi-output convolutional neural network is designed to predict the parameters of a perturbing body given the known parameters and measured perturbation (O-C). There is evidence for 3 new multi-planet candidates (WASP-18, WASP-126, TOI-193) with non-transiting companions using the 2 minute cadence observations from TESS. This approach can be used to identify multi-planet systems and stars in need of longer radial velocity and photometric follow-up than those already performed.