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

Abstract : 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} MJup, a radius of 1.865 ± 0.044 RJup, 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 ± 0.030 R, Teff = 6460 ± 140 K). A notable property of WASP-121 b is that its orbital semimajor axis is only ∼1.15 times larger than its Roche limit, which suggests that the planet is close to tidal disruption. Furthermore, its large size and extreme irradiation (∼7.1 109 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 ∼4σ, the measured occultation depth being 603 ± 130 ppm. Finally, from a measurement of the Rossiter-McLaughlin effect with the CORALIE spectrograph, we infer a sky-projected spin-orbit angle of 257.8°_{-5.5°}^{+5.3°}. 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.
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Submitted on : Thursday, June 9, 2022 - 4:47:16 PM
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L. Delrez, A. Santerne, J. -M. Almenara, D. R. Anderson, A. Collier-Cameron, et al.. WASP-121 b: a hot Jupiter close to tidal disruption transiting an active F star. Monthly Notices of the Royal Astronomical Society, 2016, 458, pp.4025-4043. ⟨10.1093/mnras/stw522⟩. ⟨insu-03691538⟩



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