Exoplanets & Exomoons

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

By Keith Cowing
Status Report
May 22, 2024
Filed under , , , , , , , , , , , , , , , ,
The Discovery and Follow-up of Four Transiting Short-period Sub-Neptunes Orbiting M dwarfs
Eccentricity distribution of planets with measured radii of 1.5 − 4R⊕ and orbital periods of ≲ 50 days around M dwarfs with Teff = 3000 − 3900 K. Only planets with measured eccentricities are shown. The color contour represents the effective temperature of a planet-hosting M dwarf. The four close-in, sub-Neptunes validated in this study are shown as red stars. astro-ph.EP

Sub-Neptunes with 2−3R 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 Rp=2.740+0.082−0.079R⊕, 2.769+0.073−0.068R, 2.120±0.067R, and 2.830+0.068−0.066R and orbital periods of P=8.02, 8.11, 5.80, and 3.08\,days, respectively. Doppler monitoring with 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.

Y. Hori, A. Fukui, T. Hirano, N. Narita, J. P. de Leon, H. T. Ishikawa, J. D. Hartman, G. Morello, N. Abreu García, L. Álvarez Hernández, V. J. S. Béjar, Y. Calatayud-Borras, I. Carleo, G. Enoc, E. Esparza-Borges, I. Fukuda, D. Galán, S. Geraldía-González, Y. Hayashi, M. Ikoma, K. Ikuta, K. Isogai, T. Kagetani, Y. Kawai, K. Kawauchi, T. Kimura, T. Kodama, J. Korth, N. Kusakabe, A. Laza-Ramos, J. H. Livingston, R. Luque, K. Miyakawa, M. Mori, S. Muñoz Torres, F. Murgas, J. Orell-Miquel, E. Palle, H. Parviainen, A. Peláez-Torres, M. Puig-Subirá, M. Sánchez-Benavente, P. Sosa-Guillén, M. Stangret, Y. Terada, N. Watanabe, G. Á. Bakos, K. Barkaoui, C. Beichman, Z. Benkhaldoun, A. W. Boyle, D. R. Ciardi, C. A. Clark, K. A. Collins, K. I. Collins, D. M. Conti, I. J.M. Crossfield, M. E. Everett, E. Furlan, M. Ghachoui, M. Gillon, E. J. Gonzales, J. Higuera, K. Horne, S. B. Howell, E. Jehin, K. V. Lester, M. B. Lund, R. Matson, E. C. Matthews, F. J. Pozuelos, B. S. Safonov, J. E. Schlieder, R. P. Schwarz, R. Sefako, G. Srdoc, I. A. Strakhov, W. C. Waalkes, C. Ziegler, D. Charbonneau, Z. Essack, M. Timmermans, N. M. Guerrero, H. Harakawa, C. Hedges, M. Ishizuka, J. M. Jenkins, M. Konishi, T. Kotani, T. Kudo, T. Kurokawa, M. Kuzuhara, J. Nishikawa, M. Omiya, G. R. Ricker, S. Seager, T. Serizawa, S. Striegel, M. Tamura, A. Ueda et al. (3 additional authors not shown)

Comments: Accepted for publication in AJ, 32 pages, 17 figures, 6 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2405.12637 [astro-ph.EP] (or arXiv:2405.12637v1 [astro-ph.EP] for this version)
Submission history
From: Yasunori Hori
[v1] Tue, 21 May 2024 09:41:42 UTC (6,653 KB)


Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻