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

Maximilian N. Günther, Didier Queloz, Edward Gillen, James McCormac, Daniel D. R. Bayliss, Francois Bouchy, Simon R. Walker, Richard G. West, Philipp Eigmüller, Alexis M. S. Smith, David J. Armstrong, Matthew Burleigh, Sarah L. Casewell, Alexander P. Chaushev, Michael R. Goad, Andrew Grange, James Jackman, James S. Jenkins, Tom M. Louden, Maximiliano MoyanoDon Pollacco, Katja Poppenhaeger, Heike Rauer, Liam Raynard, Andrew P. G. Thompson, Stéphane Udry, Christopher A. Watson, Peter J. Wheatley

Research output: Contribution to journalArticlepeer-review

18 Citations (Scopus)
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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.
Original languageEnglish
Pages (from-to)295-307
JournalMonthly Notices of the Royal Astronomical Society
Volume472
Issue number1
Early online date27 Jul 2017
DOIs
Publication statusPublished - 01 Nov 2017

Bibliographical note

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

Keywords

  • astro-ph.EP

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