TESS Hunt for Young and Maturing Exoplanets (THYME). VI. An 11 Myr Giant Planet Transiting a Very-low-mass Star in Lower Centaurus Crux

Andrew W. Mann , Mackenna L. Wood , Stephen P. Schmidt , Madyson G. Barber , James E. Owen , Benjamin M. Tofflemire , Elisabeth R. Newton , Eric E. Mamajek , Jonathan L. Bush , Gregory N. Mace , Adam L. Kraus , Pa Chia Thao , Andrew Vanderburg , Joe Llama , Christopher M. Johns-Krull , L. Prato , Asa G. Stahl , Shih-Yun Tang , Matthew J. Fields , Karen A. Collins , Kevin I. Collins , Tianjun Gan , Eric L. N. Jensen , Jacob Kamler , Richard P. Schwarz , Elise Furlan , Crystal L. Gnilka , Steve B. Howell , Kathryn V. Lester , Dylan A. Owens , Olga Suarez (1) , Djamel Mekarnia (1) , Tristan Guillot (1) , Lyu Abe (1) , Amaury H. M. J. Triaud , Marshall C. Johnson , Reilly P. Milburn , Aaron C. Rizzuto , Samuel N. Quinn , Ronan Kerr , George R. Ricker , Roland Vanderspek , David W. Latham , Sara Seager , Joshua N. Winn , Jon M. Jenkins , Natalia M. Guerrero , Avi Shporer , Joshua E. Schlieder , Brian Mclean , Bill Wohler

1 OCA - Observatoire de la Côte d'Azur

Mature super-Earths and sub-Neptunes are predicted to be ≃ Jovian radius when younger than 10 Myr. Thus, we expect to find 5-15 R _⊕ planets around young stars even if their older counterparts harbor none. We report the discovery and validation of TOI 1227b, a 0.85 ± 0.05 R _J (9.5 R _⊕) planet transiting a very-low-mass star (0.170 ± 0.015 M _⊙) every 27.4 days. TOI 1227's kinematics and strong lithium absorption confirm that it is a member of a previously discovered subgroup in the Lower Centaurus Crux OB association, which we designate the Musca group. We derive an age of 11 ± 2 Myr for Musca, based on lithium, rotation, and the color-magnitude diagram of Musca members. The TESS data and ground-based follow-up show a deep (2.5%) transit. We use multiwavelength transit observations and radial velocities from the IGRINS spectrograph to validate the signal as planetary in nature, and we obtain an upper limit on the planet mass of ≃0.5 M _J. Because such large planets are exceptionally rare around mature low-mass stars, we suggest that TOI 1227b is still contracting and will eventually turn into one of the more common <5 R _⊕ planets.

Keywords: Pre-main sequence stars; Transits; Exoplanet evolution; Exoplanet formation; Stellar associations; Stellar ages; OB associations; Time domain astronomy; Time series analysis; Late-type stars; Low mass stars; 1290; 1711; 491; 492; 1582; 1581; 1140; 2109; 1916; 909; 2050; Astrophysics - Earth and Planetary Astrophysics; Astrophysics - Solar and Stellar Astrophysics

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]

Andrew W. Mann, Mackenna L. Wood, Stephen P. Schmidt, Madyson G. Barber, James E. Owen, et al.. TESS Hunt for Young and Maturing Exoplanets (THYME). VI. An 11 Myr Giant Planet Transiting a Very-low-mass Star in Lower Centaurus Crux. The Astronomical Journal, 2022, 163, ⟨10.3847/1538-3881/ac511d⟩. ⟨insu-03656907⟩