University of Leicester
sty1193.pdf (5.66 MB)

Unmasking the hidden NGTS-3Ab: a hot Jupiter in an unresolved binary system

Download (5.66 MB)
journal contribution
posted on 2018-05-24, 10:53 authored by Maximilian N. Günther, Didier Queloz, Edward Gillen, Laetitia Delrez, François Bouchy, James McCormac, Barry Smalley, Yaseen Almleaky, David J. Armstrong, Daniel Bayliss, Artem Burdanov, Matthew Burleigh, Juan Cabrera, Sarah L. Casewell, Benjamin F. Cooke, Szilárd Csizmadia, Elsa Ducrot, Philipp Eigmüller, Anders Erikson, Boris T. Gänsicke, Neale P. Gibson, Michaël Gillon, Michael R. Goad, Emmanuël Jehin, James S. Jenkins, Tom Louden, Maximiliano Moyano, Catriona Murray, Don Pollacco, Katja Poppenhaeger, Heike Rauer, Liam Raynard, Alexis M. S. Smith, Sandrine Sohy, Samantha J. Thompson, Stéphane Udry, Christopher A. Watson, Richard G. West, Peter J. Wheatley
We present the discovery of NGTS-3Ab, a hot Jupiter found transiting the primary star of an unresolved binary system. We develop a joint analysis of multi-colour photometry, centroids, radial velocity (RV) cross-correlation function (CCF) profiles and their bisector inverse slopes (BIS) to disentangle this three-body system. Data from the Next Generation Transit Survey (NGTS), SPECULOOS and HARPS are analysed and modelled with our new blendfitter software. We find that the binary consists of NGTS-3A (G6V-dwarf) and NGTS-3B (K1V-dwarf) at <1 arcsec separation. NGTS-3Ab orbits every P = 1.675 days. The planet radius and mass are R_planet = 1.48+-0.37 R_J and M_planet = 2.38+-0.26 M_J, suggesting it is potentially inflated. We emphasise that only combining all the information from multi-colour photometry, centroids and RV CCF profiles can resolve systems like NGTS-3. Such systems cannot be disentangled from single-colour photometry and RV measurements alone. Importantly, the presence of a BIS correlation indicates a blend scenario, but is not sufficient to determine which star is orbited by the third body. Moreover, even if no BIS correlation is detected, a blend scenario cannot be ruled out without further information. The choice of methodology for calculating the BIS can influence the measured significance of its correlation. The presented findings are crucial to consider for wide-field transit surveys, which require wide CCD pixels (>5 arcsec) and are prone to contamination by blended objects. With TESS on the horizon, it is pivotal for the candidate vetting to incorporate all available follow-up information from multi-colour photometry and RV CCF profiles.


This research is based on data collected under the NGTS project at the ESO La Silla Paranal Observatory. NGTS is operated with support from the UK Science and Technology Facilities Council (STFC; project reference ST/M001962/1). Construction of the NGTS facility was funded by the University of Warwick, the University of Leicester, Queen’s University Belfast, the University of Geneva, the Deutsches Zentrum fur Luft- und Raumfahrt e.V. (DLR; under the ‘Großinvestition GI-NGTS’), the ¨ University of Cambridge and STFC. The research leading to these results has received funding from the European Research Council under the FP/2007-2013 ERC Grant Agreement number 336480 (SPECULOOS) and number 320964 (WDTracer), and from the ARC grant for Concerted Research Actions, financed by the Wallonia-Brussels Federation. This work was also partially supported by a grant from the Simons Foundation (PI Queloz, grant number 327127). This work has further made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Moreover, this publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. We make use of Python programming language (Rossum 1995) and the open-source Python packages numpy (van der Walt et al. 2011), scipy (Jones et al. 01 ), matplotlib (Hunter 2007), pandas (McKinney 2010), emcee (Foreman-Mackey et al. 2013), george (Ambikasaran et al. 2014), corner (Foreman-Mackey 2016), seaborn (https://seaborn.pydat



Monthly Notices of the Royal Astronomical Society, 2018, sty1193

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


  • VoR (Version of Record)

Published in

Monthly Notices of the Royal Astronomical Society


Oxford University Press (OUP), Royal Astronomical Society





Copyright date


Available date


Publisher version


Supplementary-data is available at



Usage metrics

    University of Leicester Publications


    No categories selected


    Ref. manager