TOI-3884 b: A rare 6-R Eplanet that transits a low-mass star with a giant and likely polar spot

ALMENARA, J.M.; BONFILS, X.; FORVEILLE, T.; ASTUDILLO-DEFRU, N.; CIARDI, D.R.; SCHWARZ, R.P.; COLLINS, K.A.; COINTEPAS, M.; LUND, M.B.; BOUCHY, F.; CHARBONNEAU, D.; DÍAZ, R.F.; DELFOSSE, X.; KIDWELL, R.C.; KUNIMOTO, M.; LATHAM, D.W.; LISSAUER, J.J.; MURGAS, F.; RICKER, G.; SEAGER, S.; VEZIE, M.; WATANABE, D.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Año: 2022 vol. 667

0004-6361

The Transiting Exoplanet Survey Satellite mission identified a deep and asymmetric transit-like signal with a periodicity of 4.5 days orbiting the M4 dwarf star TOI-3884. The signal has been confirmed by follow-up observations collected by the ExTrA facility and Las Cumbres Observatory Global Telescope, which reveal that the transit is chromatic. The light curves are well modelled by a host star having a large polar spot transited by a 6-RE planet. We validate the planet with seeing-limited photometry, high-resolution imaging, and radial velocities. TOI-3884 b, with a radius of 6:00 0:18 RE, is the first sub-Saturn planet transiting a mid-M dwarf. Owing to the host star´s brightness and small size, it has one of the largest transmission spectroscopy metrics for this planet size and becomes a top target for atmospheric characterisation with the James Webb Space Telescope and ground-based telescopes.