The Discovery and Follow-up of Four Transiting Short-period Sub-Neptunes Orbiting M Dwarfs

• Published in: The Astronomical journal Vol. 167; no. 6; pp. 289 - 313
• Main Authors: Hori, Yasunori, Fukui, Akihiko, Hirano, Teruyuki, Narita, Norio, de Leon, Jerome P., Ishikawa, Hiroyuki Tako, Hartman, Joel D., Morello, Giuseppe, García, Nestor Abreu, Hernández, Leticia Álvarez, Béjar, Víctor J. S., Calatayud-Borras, Yéssica, Carleo, Ilaria, Enoc, Gareb, Esparza-Borges, Emma, Fukuda, Izuru, Galán, Daniel, Geraldía-González, Samuel, Hayashi, Yuya, Ikoma, Masahiro, Ikuta, Kai, Isogai, Keisuke, Kagetani, Taiki, Kawai, Yugo, Kawauchi, Kiyoe, Kimura, Tadahiro, Kodama, Takanori, Korth, Judith, Kusakabe, Nobuhiko, Laza-Ramos, Andrés, Livingston, John H., Luque, Rafael, Miyakawa, Kohei, Mori, Mayuko, Murgas, Felipe, Orell-Miquel, Jaume, Palle, Enric, Parviainen, Hannu, Peláez-Torres, Alberto, Puig-Subirà, Marta, Sánchez-Benavente, Manuel, Sosa-Guillén, Paula, Stangret, Monika, Muñoz Torres, Sara, Watanabe, Noriharu, Bakos, Gaspar Á., Barkaoui, Khalid, Beichman, Charles, Benkhaldoun, Zouhair, Boyle, Andrew W., Ciardi, David R., Clark, Catherine A., Collins, Karen A., Collins, Kevin I., Crossfield, Ian J.M., Everett, Mark E., Furlan, Elise, Ghachoui, Mourad, Gillon, Michaël, Gonzales, Erica J., Higuera, Jesus, Horne, Keith, Howell, Steve B., Lester, Kathryn V., Lund, Michael B., Matson, Rachel, Matthews, Elisabeth C., Pozuelos, Francisco J., Safonov, Boris S., Schlieder, Joshua E., Schwarz, Richard P., Sefako, Ramotholo, Srdoc, Gregor, Strakhov, Ivan A., Timmermans, Mathilde, Waalkes, William C., Ziegler, Carl, Charbonneau, David, Essack, Zahra, Guerrero, Natalia M., Harakawa, Hiroki, Hedges, Christina, Ishizuka, Masato, Jenkins, Jon M., Konishi, Mihoko, Kotani, Takayuki, Kudo, Tomoyuki, Kurokawa, Takashi, Kuzuhara, Masayuki, Nishikawa, Jun, Omiya, Masashi, Ricker, George R., Seager, Sara, Serizawa, Takuma, Striegel, Stephanie, Tamura, Motohide, Ueda, Akitoshi, Vanderspek, Roland, Vievard, Sébastien, Winn, Joshua N.
• Format: Journal Article Web Resource
• Language: English
• Published: Madison The American Astronomical Society 01.06.2024; IOP Publishing; IOP
• Subjects: Astronomi, astrofysik och kosmologi; Astronomy, Astrophysics and Cosmology; Aérospatiale, astronomie & astrophysique; Exoplanets; Extrasolar planets; Fysik; Ground-based observation; Infrared instruments; Interiors; M dwarf stars; Mini Neptunes; Natural Sciences; Naturvetenskap; Orbits; Physical Sciences; Physical, chemical, mathematical & earth Sciences; Physique, chimie, mathématiques & sciences de la terre; Planetary evolution; Planets; Radial velocity; Red dwarf stars; Space science, astronomy & astrophysics; Statistical analysis; Terrestrial planets; Tides; Transit photometry
• ISSN: 0004-6256; 1538-3881; 1538-3881
• DOI: 10.3847/1538-3881/ad4115

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 R p = 2.740 − 0.079 + 0.082 R ⊕ , 2.769 − 0.068 + 0.073 R ⊕ , 2.120 ± 0.067 R ⊕ , and 2.830 − 0.066 + 0.068 R ⊕ 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 2 σ 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.