WASP-121 b: a hot Jupiter close to tidal disruption transiting an active F star

L. Delrez, A. Santerne, J.-M. Almenara, D.~R. Anderson, A. Collier-Cameron, R.~F. Díaz, Michael Gillon, C. Hellier, E. Jehin, M. Lendl, P.~F.~L. Maxted, M. Neveu-VanMalle, F. Pepe, D. Pollacco, Didier Queloz, D. Ségransan, B. Smalley, A.~M.~S. Smith, A.~H.~M.~J. Triaud, S. UdryV. Van Grootel, R.~G. West

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57 Citations (Scopus)


We present the discovery by the WASP-South survey of WASP-121 b, a new remarkable short-period transiting hot Jupiter. The planet has a mass of 1.183$$-0.062$$$$+0.064$$ M$_Jup$, a radius of 1.865 plusmn 0.044 R$_Jup$, and transits every 1.274 9255$$-0.000 0025$$$$+0.000 0020$$ days an active F6-type main-sequence star (V = 10.4, 1.353$$-0.079$$$$+0.080$$ M$_⊙$, 1.458 plusmn 0.030 R$_⊙$, T$_eff$ = 6460 plusmn 140 K). A notable property of WASP-121 b is that its orbital semimajor axis is only tilde1.15 times larger than its Roche limit, which suggests that the planet is close to tidal disruption. Furthermore, its large size and extreme irradiation (tilde7.1 10$^9$ erg s$^-1$ cm$^-2$) make it an excellent target for atmospheric studies via secondary eclipse observations. Using the TRAnsiting Planets and PlanetesImals Small Telescope, we indeed detect its emission in the z$^'$-band at better than tilde4$, the measured occultation depth being 603 plusmn 130 ppm. Finally, from a measurement of the Rossiter-McLaughlin effect with the CORALIE spectrograph, we infer a sky-projected spin-orbit angle of 257.8deg$$-5.5deg$$$$+5.3deg$$. This result may suggest a significant misalignment between the spin axis of the host star and the orbital plane of the planet. If confirmed, this high misalignment would favour a migration of the planet involving strong dynamical events with a third body.
Original languageEnglish
Pages (from-to)4025-4043
Number of pages19
JournalRoyal Astronomical Society. Monthly Notices
Early online date11 Mar 2016
Publication statusPublished - 1 Jun 2016


  • planetary systems
  • techniques: photometric
  • techniques: radial velocities
  • techniques: spectroscopic
  • stars: individual: WASP-121


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