WASP-128b: a transiting brown dwarf in the dynamical-tide regime

V. Hodžić, A. H. M. J. Triaud, D. R. Anderson, F. Bouchy, A. Collier Cameron, L. Delrez, M. Gillon, C. Hellier, E. Jehin, M. Lendl, P. F. L. Maxted, F. Pepe, D. Pollacco, D. Queloz, D. Ségransan, B. Smalley, S. Udry, R. West

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Massive companions in close orbits around G dwarfs are thought to undergo rapid orbital decay due to runaway tidal dissipation. We report here the discovery of WASP-128b, a brown dwarf discovered by the WASP survey transiting a G0V host on a 2.2d orbit, where the measured stellar rotation rate places the companion in a regime where tidal interaction is dominated by dynamical tides. Under the assumption of dynamical equilibrium, we derive a value of the stellar tidal quality factor logQ′=6.96±0.19. A combined analysis of ground-based photometry and high-resolution spectroscopy reveals a mass and radius of the host, M=1.16±0.04M, R=1.16±0.02R, and for the companion, Mb=37.5±0.8MJRb=0.94±0.02RJ, placing WASP-128b in the driest parts of the brown dwarf desert, and suggesting a mild inflation for its age. We estimate a remaining lifetime for WASP-128b similar to that of some ultra-short period massive hot Jupiters, and note it may be a propitious candidate for measuring orbital decay and testing tidal theories.
Original languageEnglish
Pages (from-to)5091–5097
Number of pages7
JournalRoyal Astronomical Society. Monthly Notices
Issue number4
Early online date14 Sept 2018
Publication statusPublished - 21 Dec 2018

Bibliographical note

7 pages, 3 figures. Accepted in MNRAS. Added references, fixed typos, and clarified some parts of the text


  • astro-ph.EP
  • astro-ph.SR
  • methods: data analysis
  • planets and satellites: dynamical evolution and stability
  • binaries: eclipsing
  • brown dwarfs


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