The Discovery and Follow-up of Four Transiting Short-period Sub-Neptunes Orbiting M Dwarfs
Lester, Kathryn V.; Ikuta, Kai; Tamura, Motohide; Schlieder, Joshua E.; Howell, Steve B.; Miyakawa, Kohei; Hirano, Teruyuki; Crossfield, Ian J. M.; Horne, Keith; Ziegler, Carl; Collins, Karen A.; Ricker, George R.; Vanderspek, Roland; Seager, Sara; Winn, Joshua N.; Jenkins, Jon M.; Kudo, Tomoyuki; Barkaoui, Khalid; Collins, Kevin I.; Ciardi, David R.; Livingston, John H.; de Leon, Jerome P.; Fukui, Akihiko; Korth, Judith; Kuzuhara, Masayuki; Narita, Norio; Palle, Enric; Hedges, Christina; Lund, Michael B.; Gillon, Michaël; Clark, Catherine A.; Everett, Mark E.; Luque, Rafael; Hartman, Joel D.; Konishi, Mihoko; Terada, Yuka; Pozuelos, Francisco J.; Jehin, Emmanuël; Sefako, Ramotholo; Omiya, Masashi; Harakawa, Hiroki; Charbonneau, David; Morello, Giuseppe; Kusakabe, Nobuhiko; Beichman, Charles; Gonzales, Erica J.; Schwarz, Richard P.; Murgas, Felipe; Matthews, Elisabeth C.; Furlan, Elise; Conti, Dennis M.; Essack, Zahra; Striegel, Stephanie; Carleo, Ilaria; Kawauchi, Kiyoe; Orell-Miquel, Jaume; Srdoc, Gregor; Hori, Yasunori; Nishikawa, Jun; Ishikawa, Hiroyuki Tako; Kotani, Takayuki; Kurokawa, Takashi; Ueda, Akitoshi; Parviainen, Hannu; Esparza-Borges, Emma; Kodama, Takanori; Matson, Rachel; Benkhaldoun, Zouhair; Isogai, Keisuke; Ikoma, Masahiro; Strakhov, Ivan A.; Mori, Mayuko; Watanabe, Noriharu; Ghachoui, Mourad; Timmermans, Mathilde; Guerrero, Natalia M.; Kagetani, Taiki; Kimura, Tadahiro; Serizawa, Takuma; Boyle, Andrew W.; Safonov, Boris S.; Waalkes, William C.; Higuera, Jesus; Vievard, Sébastien; Fukuda, Izuru; Bakos, Gaspar Á.; Béjar, Víctor J. S.; Sánchez-Benavente, Manuel; Stangret, Monika; Kawai, Yugo; Ishizuka, Masato; Calatayud-Borras, Yéssica; Galán, Daniel; Geraldía-González, Samuel; Hayashi, Yuya; Laza-Ramos, Andrés; Muñoz Torres, Sara; Peláez-Torres, Alberto; García, Nestor Abreu; Álvarez Hernández, Leticia; Enoc, Gareb; Puig-Subirà, Marta; Sosa-Guillén, Paula
Japan, Spain, Canada, United States, Sweden, Italy, Taiwan, Belgium, Morocco, United Kingdom, Germany, Russia, South Africa, Croatia
Abstract
Sub-Neptunes with radii of 2–3 R ⊕ are intermediate in size between rocky planets and Neptune-sized planets. The orbital properties and bulk compositions of transiting sub-Neptunes provide clues to the formation and evolution of close-in small planets. In this paper, we present the discovery and follow-up of four sub-Neptunes orbiting M dwarfs (TOI-782, TOI-1448, TOI-2120, and TOI-2406), three of which were newly validated by ground-based follow-up observations and statistical analyses. TOI-782 b, TOI-1448 b, TOI-2120 b, and TOI-2406 b have radii of , , 2.120 ± 0.067 R ⊕, and and orbital periods of P = 8.02, 8.11, 5.80, and 3.08 days, respectively. Doppler monitoring with the Subaru/InfraRed Doppler instrument led to 2σ upper limits on the masses of <19.1 M ⊕, <19.5 M ⊕, <6.8 M ⊕, and <15.6 M ⊕ for TOI-782 b, TOI-1448 b, TOI-2120 b, and TOI-2406 b, respectively. The mass–radius relationship of these four sub-Neptunes testifies to the existence of volatile material in their interiors. These four sub-Neptunes, which are located above the so-called "radius valley," are likely to retain a significant atmosphere and/or an icy mantle on the core, such as a water world. We find that at least three of the four sub-Neptunes (TOI-782 b, TOI-2120 b, and TOI-2406 b), orbiting M dwarfs older than 1 Gyr, are likely to have eccentricities of e ∼ 0.2–0.3. The fact that tidal circularization of their orbits is not achieved over 1 Gyr suggests inefficient tidal dissipation in their interiors.