Single transit candidates from K2: detection and period estimation

Abstract

Photometric surveys such as Kepler have the precision to identify exoplanet and eclipsing binary candidates from only a single transit. K2, with its 75 d campaign duration, is ideally suited to detect significant numbers of single-eclipsing objects. Here we develop a Bayesian transit-fitting tool ('Namaste: An Mcmc Analysis of Single Transit Exoplanets') to extract orbital information from single transit events. We achieve favourable results testing this technique on known Kepler planets, and apply the technique to seven candidates identified from a targeted search of K2 campaigns 1, 2 and 3. We find EPIC203311200 to host an excellent exoplanet candidate with a period, assuming zero eccentricity, of 540 +410 −230 d and a radius of 0.51 ± 0.05R Jup . We also find six further transit candidates for which more follow-up is required to determine a planetary origin. Such a technique could be used in the future with TESS, PLATO and ground-based photometric surveys such as NGTS, potentially allowing the detection of planets in reach of confirmation by Gaia.

Estimation of singly transiting K2 planet periods with Gaia parallaxes

“…As a result, transit observations of relatively long-period exoplanets are rare, even as long-period exoplanets themselves merit intense study. Planets with long periods relative to the Kepler baseline (∼ 1500 days), for example, are interesting as analogs to the outer planets of the Solar System, and as examples of planets at or beyond the snow line servational baseline over each observed field (∼ 75 days), Osborn et al (2016) identify 7 single-transit candidates. La-Course & Jacobs (2018) catalogue 164 single-transit events, although they caution that most are likely eclipsing binaries.…”

NGTS and WASP photometric recovery of a single-transit candidate from TESS

“…Before beginning our search, we flattened each light curve using the Lightkurve tool, part of the publicly-available Kepler/K2 community tools (Lightkurve Collaboration et al 2018). These flattened light curves were then searched systematically using the method set out in Osborn et al (2016), searching for single-transit events up to 24 h in duration. We detected on order of 1000 high signal-to-noise-ratio events per sector.…”

Measuring the Galactic Distribution of Transiting Planets with WFIRST

“…Even for the cases for which only one transit is observed, it should still be possible to place constraints on the period using these methods, and where possible, prompt RV observations would be extremely beneficial (Yee & Gaudi 2008). A few dozen singly transiting were planets detected in the Kepler and K2 data, largely through visual inspection (Wang et al 2015b;Osborn et al 2016;Uehara et al 2016;Foreman-Mackey et al 2016). The probability of detecting a singly transiting planet with WFIRST scales as P −5/3 , so most detections of single transits will be of planets with shorter orbital periods.…”