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

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posted on 2020-04-21, 17:12 authored by JAG Jackman, PJ Wheatley, D Bayliss, S Gill, ST Hodgkin, MR Burleigh, IP Braker, MN Günther, T Louden, O Turner, DR Anderson, C Belardi, F Bouchy, JT Briegal, EM Bryant, J Cabrera, SL Casewell, A Chaushev, JC Costes, S Csizmadia, P Eigmüller, A Erikson, BT Gänsicke, E Gillen, MR Goad, JS Jenkins, J McCormac, M Moyano, LD Nielsen, D Pollacco, K Poppenhaeger, D Queloz, H Rauer, L Raynard, AMS Smith, S Udry, JI Vines, CA Watson, RG West
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 arcsec with very similar proper motion and systemic velocity, suggesting the NGTS-7 system is a hierarchical triple. The wide stellar companion is likely to have driven the migration of the brown dwarf through the Kozai-Lidov mechanism. 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.


This research is based on data collected under the NGTS project at the ESO La Silla Paranal Observatory. The NGTS facility is funded by a consortium of institutes consisting of the University of Warwick, the University of Leicester, Queen’s University Belfast, the University of Geneva, the Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR; under the ‘Großinvestition GI-NGTS’), and the University of Cambridge, together with the UK Science and Technology Facilities Council (STFC; project reference ST/M001962/1 and ST/S002642/1). JAGJ was supported by STFC PhD studentship 176309. PJW, SG, TL, BTG, DP, and RGW were supported by STFC consolidated grant ST/P000495/1. SLC was supported by an STFC Ernest Rutherford fellowship. MNG acknowledges support from MIT’s Kavli Institute as a Torres Postdoctoral Fellow. JSJ acknowledges support by Fondecyt grant 1161218 and partial support by CATA-Basal (PB06, CONICYT). CAW acknowledges support from Science and Technology Facilities Council grant ST/P000312/1. EG gratefully acknowledges support from the David and Claudia Harding Foundation in the form of a Winton Exoplanet Fellowship.



Monthly Notices of the Royal Astronomical Society, Volume 489, Issue 4, November 2019, Pages 5146–5164

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


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Oxford University Press (OUP), Royal Astronomical Society



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