TOI-2084 b and TOI-4184 b: Two new sub-Neptunes around M dwarf stars

Barkaoui, K.; Timmermans, M.; Soubkiou, A.; Rackham, B. V.; Burgasser, A. J.; Chouqar, J.; Pozuelos, F. J.; Collins, K. A.; Howell, S. B.; Simcoe, R.; Melis, C.; Stassun, K. G.; Tregloan-Reed, J.; Cointepas, M.; Gillon, M.; Bonfils, X.; Furlan, E.; Gnilka, C. L.; Almenara, J. M.; Alonso, R.; Benkhaldoun, Z.; Bonavita, M.; Bouchy, F.; Burdanov, A.; Chinchilla, P.; Davoudi, F.; Delrez, L.; Demangeon, O.; Dominik, M.; Demory, B. -O.; de Wit, J.; Dransfield, G.; Ducrot, E.; Fukui, A.; Hinse, T. C.; Hooton, M. J.; Jehin, E.; Jenkins, J. M.; Jørgensen, U. G.; Latham, D. W.; Garcia, L.; Carrazco-Gaxiola, S.; Ghachoui, M.; Gómez Maqueo Chew, Y.; Günther, M. N.; McCormac, J.; Murgas, F.; Murray, C. A.; Narita, N.; Niraula, P.; Pedersen, P. P.; Queloz, D.; Rebolo, R.; Ricker, G.; Sabin, L.; Sajadian, S.; Schanche, N.; Schwarz, R. P.; Seager, S.; Sebastian, D.; Sefako, R.; Sohy, S.; Southworth, J.; Srdoc, G.; Thompson, S. J.; Triaud, A. H. M. J.; Vanderspek, R.; Wells, R. D.; Winn, J. N.; Zúñiga-Fernández, S.
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Astronomy and Astrophysics

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We present the discovery and validation of two TESS exoplanets orbiting nearby M dwarfs: TOI-2084 b, and TOI-4184b. We characterized the host stars by combining spectra from Shane/Kast and Magellan/FIRE, spectral energy distribution analysis, and stellar evolutionary models. In addition, we used Gemini-South/Zorro & -North/Alopeke high-resolution imaging, archival science images, and statistical validation packages to support the planetary interpretation. We performed a global analysis of multi-colour photometric data from TESS and ground-based facilities in order to derive the stellar and planetary physical parameters for each system. We find that TOI-2084 band TOI-4184 bare sub-Neptune-sized planets with radii of Rp = 2.47 ± 0.13R⊕ and Rp = 2.43 ± 0.21 R⊕, respectively. TOI-2084 b completes an orbit around its host star every 6.08 days, has an equilibrium temperature of Teq = 527 ± 8 K and an irradiation of Sp = 12.8 ± 0.8 S⊕. Its host star is a dwarf of spectral M2.0 ± 0.5 at a distance of 114 pc with an effective temperature of Teff = 3550 ± 50 K, and has a wide, co-moving M8 companion at a projected separation of 1400 au. TOI-4184 b orbits around an M5.0 ± 0.5 type dwarf star (Kmag = 11.87) each 4.9 days, and has an equilibrium temperature of Teq = 412 ± 8 K and an irradiation of Sp = 4.8 ± 0.4 S⊕. TOI-4184 is a metal poor star ([Fe/H] = −0.27 ± 0.09 dex) at a distance of 69 pc with an effective temperature of Teff = 3225 ± 75 K. Both planets are located at the edge of the sub-Jovian desert in the radius-period plane. The combination of the small size and the large infrared brightness of their host stars make these new planets promising targets for future atmospheric exploration with JWST.
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