NGTS-7Ab: An ultra-short period brown dwarf transiting a tidally-locked and active M dwarf

James A. G. Jackman, Peter J. Wheatley, Dan Bayliss, Samuel Gill, Simon T. Hodgkin, Matthew R. Burleigh, Ian P. Braker, Maximilian N. Günther, Tom Louden, Oliver Turner, David R. Anderson, Claudia Belardi, François Bouchy Joshua T. Briegal, Edward M. Bryant, Juan Cabrera, Sarah L. Casewell, Alexander Chaushev, Jean C. Costes, Szilard Csizmadia, Philipp EigmüllerAnders Erikson, Boris T. Gänsicke, Edward Gillen, Michael R. Goad, James S. Jenkins, James McCormac, Maximiliano Moyano, Louise D. Nielsen, Don Pollacco, Katja Poppenhaeger, Didier Queloz, Heike Rauer, Liam Raynard, Alexis M. S. Smith, Stéphane Udry, Jose I. Vines, Christopher A. Watson, Richard G. West

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Abstract

We present the discovery of NGTS-7Ab, a high mass brown dwarf transiting an M dwarf with a period of 16.2 hours, discovered as part of the Next Generation Transit Survey (NGTS). This is the shortest period transiting brown dwarf around a main or pre-main sequence star to date. The M star host (NGTS-7A) has an age of roughly 55 Myr and is in a state of spin-orbit synchronisation, which we attribute to tidal interaction with the brown dwarf acting to spin up the star. The host star is magnetically active and shows multiple flares across the NGTS and follow up lightcurves, which we use to probe the flare-starspot phase relation. The host star also has an M star companion at a separation of 1.13 arcseconds with very similar proper motion and systemic velocity, suggesting the NGTS-7 system is a hierarchical triple. The combination of tidal synchronisation and magnetic braking is expected to drive ongoing decay of the brown dwarf orbit, with a remaining lifetime of only 5-10 Myr.
Original languageEnglish
JournalMonthly Notices of the Royal Astronomical Society, Advance Access
DOIs
Publication statusPublished - 11 Sep 2019

Keywords

  • stars: brown dwarfs
  • stars: low mass
  • stars: rotation
  • stars: individual: NGTS-7A
  • stars: flare

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