Exoplanets, -moons, -comets

The Mass Of TOI-654 b: A Short-period Sub-Neptune Transiting A Mid-M Dwarf

By Keith Cowing

Status Report

astro-ph.EP

July 23, 2025

Filed under Ariel mission, astro-ph.EP, exoplanet, JWST, M dwarf, MuSCAT, sub-Neptune, Subaru telescope, TESS, TOI-654, TOI-654 b

The Mass Of TOI-654 b: A Short-period Sub-Neptune Transiting A Mid-M Dwarf — Multicolor simultaneous light curves in g-, r-, i-, and zs-bands, obtained by MuSCAT2 on 2021 March 19 (Top) and MuSCAT3 on 2021 January 28 (Bottom) (Section 2.2 and 2.3). The data are jointly fitted with the transit model (blue, green, orange, and red) and baseline model, and the data are subtracted with the baseline models (gray). Alt text: Time-series flux for the transits of the MuSCAT2 and MuSCAT3 data in g-, r-, i-, and zs-bands, and the optimum models for each. — astro-ph.EP

Sub-Neptunes are small planets between the size of the Earth and Neptune. The orbital and bulk properties of transiting sub-Neptunes can provide clues for their formation and evolution of small planets.

In this paper, we report on follow-up observations of a planetary system around the mid-M dwarf TOI-654, whose transiting sub-Neptune TOI-654 b (P=1.53 day) is validated as a suitable target for the atmospheric observation.

We measure the planetary mass and stellar properties with the InfraRed Doppler instrument (IRD) mounted on the Subaru telescope and obtain the stellar and planetary properties from additional transit observations by the Transit Exoplanetary Survey Satellite (TESS) and a series of the Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets (MuSCAT). As a result, the planetary mass of TOI-654 b is determined to be M_p=8.71±1.25M_⊕, and the radius is updated to be R_p=2.378±0.089R_⊕.

The bulk density suggests that the planet is composed of a rocky and volatile-rich core or a rocky core surrounded by a small amount of H/He this http URL-654 b is one of unique planets located around the radius valley and and also on the outer edge of the Neptune desert.

The precise mass determination enables us to constrain the atmospheric properties with future spectroscopic observations especially for the emission by the James Webb Space Telescope and Ariel.

Kai Ikuta, Norio Narita, Takuya Takarada, Teruyuki Hirano, Akihiko Fukui, Hiroyuki Tako Ishikawa, Yasunori Hori, Tadahiro Kimura, Takanori Kodama, Masahiro Ikoma, Jerome P. de Leon, Kiyoe Kawauchi, Masayuki Kuzuhara, Gaia Lacedelli, John H. Livingston, Mayuko Mori, Felipe Murgas, Enric Palle, Hannu Parviainen, Noriharu Watanabe, Izuru Fukuda, Hiroki Harakawa, Yuya Hayashi, Klaus Hodapp, Keisuke Isogai, Taiki Kagetani, Yugo Kawai, Vigneshwaran Krishnamurthy, Tomoyuki Kudo, Takashi Kurokawa, Nobuhiko Kusakabe, Jun Nishikawa, Stevanus K. Nugroho, Masashi Omiya, Takuma Serizawa, Aoi Takahashi, Huan-Yu Teng, Yuka Terada, Akitoshi Ueda, Sébastien Vievard, Yujie Zou, Takayuki Kotani, Motohide Tamura

Comments: 15 pages, 11 figures, accepted for publication in PASJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2507.16222 [astro-ph.EP] (or arXiv:2507.16222v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2507.16222
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Submission history
From: Kai Ikuta
[v1] Tue, 22 Jul 2025 04:35:27 UTC (4,413 KB)
https://arxiv.org/abs/2507.16222
Astrobiology,

Keith Cowing

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) 🖖🏻

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