An automated method to detect transiting circumbinary planets

Abstract

To date a dozen transiting "Tatooines" or circumbinary planets (CBPs) have been discovered, by eye, in the data from the Kepler mission; by contrast, thousands of confirmed circumstellar planets orbiting around single stars have been detected using automated algorithms. Automated detection of CBPs is challenging because their transits are strongly aperiodic with irregular profiles. Here, we describe an efficient and automated technique for detecting circumbinary planets that transit their binary hosts in Kepler light curves. Our method accounts for large transit timing and duration variations (TTVs and TDVs), induced by binary reflex motion, in two ways: 1) We directly correct for large-scale TTVs and TDVs in the light curves by using Keplerian models to approximate binary and CBP orbits; and 2) We allow additional aperiodicities on the corrected light curves by employing the Quasi-periodic Automated Transit Search algorithm (QATS). We demonstrate that our method dramatically improves detection significance using simulated data and two previously identified CBP systems, Kepler -35 and Kepler -64.

TOI-1338: TESS’ First Transiting Circumbinary Planet

“…This is demonstrated in Figure 21, where it resides on the very tail of the TESS planet candidate period distribution. We note that the current lack of small CBPs is likely an observational bias, since unique challenges have inhibited their detection to date, largely as a result of the transit timing variations induced by the barycentric binary motion and the orbital dynamics (Armstrong et al 2014;Windemuth et al 2019). The CBP population is yet to be constrained below 4R ⊕ (Armstrong et al 2014), and we expect that the large quantity and brightness of the TESS stars will enable the expansion of this parameter space.…”

Science merit function for the Kepler mission

“…The nonrepetitive transit patterns from planets orbiting binary stars were much more difficult to detect than those from single stars. 39 Furthermore, the secondary star diluted the transit depth. Both effects would cause transit patterns to be missed.…”

TIC 172900988: A Transiting Circumbinary Planet Detected in One Sector of TESS Data

“…The transits are shallower (due to the constant "third-light" dilution from the binary companion), noisier (due to starspots and stellar activity from two stars), and can be blended with the stellar eclipses. 68 This difficulty is greatly compounded when the observations cover a single conjunction and, even if multiple transits are detected as in the system presented here, they are neither periodic, nor have the same depth and duration (e.g., Kostov et al 2014;Windemuth et al 2019;Martin & Fabrycky 2021). The transit times and shapes depend on the orientation and motion of the binary stars and of the CBP at the observed times.…”

“…The longer period is due to the stability requirement around the binary, coupled with the lack of CBPs around the shortest-period binaries (Armstrong et al 2014;Martin & Triaud 2015;Welsh et al 2014). The larger radius is possibly a detection bias against finding smaller planets due to the CBPs' being intrinsically more difficult to detect than planets orbiting a single star (see, e.g., Windemuth et al 2019;Martin & Fabrycky 2021). Yet the CBPs have smaller radii, on average, than the hot Jupiter subset.…”