Publication Date:
2016-04-09
Description:
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 ± 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 ± 0.030 R , T eff = 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 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 ~4, 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 $257{^{\circ}_{.}} 8_{-5{^{\circ}_{.}} 5}^{+5{^{\circ}_{.}} 3}$ . 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.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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