TOI-1201 b: A mini-Neptune transiting a bright and moderately young M dwarf

Kossakowski, D.; Kemmer, J.; Bluhm, P.; Stock, S.; Caballero, J. A.; Béjar, V. J. S.; Cardona Guillén, C.; Lodieu, N.; Collins, K. A.; Oshagh, M.; Schlecker, M.; Espinoza, N.; Pallé, E.; Henning, Th.; Kreidberg, L.; Kürster, M.; Amado, P. J.; Anderson, D. R.; Morales, J. C.; Cartwright, S.; Charbonneau, D.; Chaturvedi, P.; Cifuentes, C.; Conti, D. M.; Cortés-Contreras, M.; Dreizler, S.; Galadí-Enríquez, D.; Guerra, P.; Hart, R.; Hellier, C.; Henze, C.; Herrero, E.; Jeffers, S. V.; Jenkins, J. M.; Jensen, E. L. N.; Kaminski, A.; Kielkopf, J. F.; Kunimoto, M.; Lafarga, M.; Latham, D. W.; Lillo-Box, J.; Luque, R.; Molaverdikhani, K.; Montes, D.; Morello, G.; Morgan, E. H.; Nowak, G.; Pavlov, A.; Perger, M.; Quintana, E. V.; Quirrenbach, A.; Reffert, S.; Reiners, A.; Ricker, G.; Ribas, I.; López, C. Rodríguez; Osorio, M. R. Zapatero; Seager, S.; Schöfer, P.; Schweitzer, A.; Trifonov, T.; Vanaverbeke, S.; Vanderspek, R.; West, R.; Winn, J.; Zechmeister, M.
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Astronomy and Astrophysics

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We present the discovery of a transiting mini-Neptune around TOI-1201, a relatively bright and moderately young early M dwarf (J ≈ 9.5 mag, ~600-800 Myr) in an equal-mass ~8 arcsecond-wide binary system, using data from the Transiting Exoplanet Survey Satellite, along with follow-up transit observations. With an orbital period of 2.49 d, TOI-1201 b is a warm mini-Neptune with a radius of Rb = 2.415 ± 0.090 R⊕. This signal is also present in the precise radial velocity measurements from CARMENES, confirming the existence of the planet and providing a planetary mass of Mb = 6.28 ± 0.88 M⊕ and, thus, an estimated bulk density of 2.45−0.42+0.48 g cm−3. The spectroscopic observations additionally show evidence of a signal with a period of 19 d and a long periodic variation of undetermined origin. In combination with ground-based photometric monitoring from WASP-South and ASAS-SN, we attribute the 19 d signal to the stellar rotation period (Prot = 19-23 d), although we cannot rule out that the variation seen in photometry belongs to the visually close binary companion. We calculate precise stellar parameters for both TOI-1201 and its companion. The transiting planet is anexcellent target for atmosphere characterization (the transmission spectroscopy metric is 97−16+21) with the upcoming James Webb Space Telescope. It is also feasible to measure its spin-orbit alignment via the Rossiter-McLaughlin effect using current state-of-the-art spectrographs with submeter per second radial velocity precision.

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