TY - JOUR
T1 - Centroid vetting of transiting planet candidates from the Next Generation Transit Survey
AU - Günther, Maximilian N.
AU - Queloz, Didier
AU - Gillen, Edward
AU - McCormac, James
AU - D. R. Bayliss, Daniel
AU - Bouchy, Francois
AU - Walker, Simon R.
AU - West, Richard G.
AU - Eigmüller, Philipp
AU - Smith, Alexis M. S.
AU - Armstrong, David J.
AU - Burleigh, Matthew
AU - Casewell, Sarah L.
AU - Chaushev, Alexander P.
AU - Goad, Michael R.
AU - Grange, Andrew
AU - Jackman, James
AU - Jenkins, James S.
AU - M. Louden, Tom
AU - Moyano, Maximiliano
AU - Pollacco, Don
AU - Poppenhaeger, Katja
AU - Rauer, Heike
AU - Raynard, Liam
AU - Thompson, Andrew P. G.
AU - Udry, Stéphane
AU - Watson, Christopher A.
AU - J. Wheatley, Peter
N1 - Accepted for publication in MNRAS 25 Jul 2017. 15 pages, 15 figures, 3 tables. This is the authors' version of the manuscript
PY - 2017/11/1
Y1 - 2017/11/1
N2 - 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.
AB - 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.
KW - astro-ph.EP
U2 - 10.1093/mnras/stx1920
DO - 10.1093/mnras/stx1920
M3 - Article
SN - 0035-8711
VL - 472
SP - 295
EP - 307
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 1
ER -