Centroid vetting of transiting planet candidates from the Next Generation Transit Survey

Abstract

The Next Generation Transit Survey (NGTS), operating in Paranal since 2016, is a wide-field survey to detect Neptunes and super-Earths transiting bright stars, which are suitable for precise radial velocity follow-up and characterisation. Thereby, its sub-mmag photometric precision and ability to identify false positives are crucial. Particularly, variable background objects blended in the photometric aperture frequently mimic Neptune-sized transits and are costly in follow-up time. These objects can best be identified with the centroiding technique: if the photometric flux is lost off-centre during an eclipse, the flux centroid shifts towards the centre of the target star. Although this method has successfully been employed by the Kepler mission, it has previously not been implemented from the ground. We present a fully-automated centroid vetting algorithm developed for NGTS, enabled by our high-precision auto-guiding. Our method allows detecting centroid shifts with an average precision of 0.75 milli-pixel, and down to 0.25 milli-pixel for specific targets, for a pixel size of 4.97 arcsec. The algorithm is now part of the NGTS candidate vetting pipeline and automatically employed for all detected signals. Further, we develop a joint Bayesian fitting model for all photometric and centroid data, allowing to disentangle which object (target or background) is causing the signal, and what its astrophysical parameters are. We demonstrate our method on two NGTS objects of interest. These achievements make NGTS the first ground-based wide-field transit survey ever to successfully apply the centroiding technique for automated candidate vetting, enabling the production of a robust candidate list before follow-up.

arXiv commentAccepted for publication in MNRAS 25 Jul 2017. 15 pages, 15 figures, 3 tables. This is the authors' version of the manuscript

References in corpus (16)

• emcee: The MCMC Hammer
• The NumPy array: a structure for efficient numerical computation
• The Gaia mission
• Analytic Lightcurves for Planetary Transit Searches
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• The false positive rate of Kepler and the occurrence of planets
• Eclipsing binaries in open clusters. II. V453 Cyg in NGC 6871
• The Next Generation Transit Survey (NGTS)
• Identification of Background False Positives from Kepler Data
• LSPM J1112+7626: detection of a 41-day M-dwarf eclipsing binary from the MEarth transit survey
• Pre-Spectroscopic False Positive Elimination of Kepler Planet Candidates
• Eclipsing binaries in open clusters. III. V621 Per in chi Persei
• New low-mass eclipsing binary systems in Praesepe discovered by K2
• DONUTS: A science frame autoguiding algorithm with sub-pixel precision, capable of guiding on defocused stars
• A Low-Mass Exoplanet Candidate Detected By $K2$ Transiting the Praesepe M Dwarf JS 183
• A New Yield Simulator for Transiting Planets and False Positives: Application to the Next Generation Transit Survey

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• Following the TraCS of exoplanets with Pan-Planets: Wendelstein-1b and Wendelstein-2b
• High-precision light curves of geostationary objects: The PHANTOM ECHOES 2 RPO campaign
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