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

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. GänsickeNeale 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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)
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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 multicolour 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 (K1Vdwarf) at < 1 arcsec separation. NGTS-3Ab orbits every 1.675 d. The planet radius and mass are Rplanet = 1.48 ± 0.37 RJ and Mplanet = 2.38 ± 0.26MJ, suggesting it is potentially inflated. We emphasize that only combining all the information frommulticolour 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 multicolour photometry and RV CCF profiles.

Original languageEnglish
Pages (from-to)4720-4737
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date07 May 2018
Publication statusPublished - Aug 2018


  • Binaries: eclipsing
  • Eclipses
  • Occultations
  • Planets and satellites: detection
  • Surveys

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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