Exoplanets & Exomoons

TOI-1801 b: A Temperate Mini-Neptune Around A Young M0.5 Dwarf

By Keith Cowing
Status Report
October 17, 2023
Filed under , , , , , , ,
TOI-1801 b: A Temperate Mini-Neptune Around A Young M0.5 Dwarf
Mass-radius diagram for TOI-1801 b, together with all known exoplanets (grey dots) with a precision better than 8% in radius (through transit) and 20% in mass (from RV). The population of young transiting exoplanets (< 900 Myr) with measured masses is plotted as coloured dots, according to their ages. The uncertainties on TOI-1801 b are shown as coloured shaded regions with 1, 2, and 3σ levels of confidence. In the left panel, the iso-density lines are displayed as dashed grey lines. In the remaining panels where the population of exoplanets is plotted along with TOI-1801 b, coloured lines indicate different composition models without gas (middle panel) and with a gas envelope (right panel) from Zeng et al. (2019). In the right panel, the solid and dotted lines show the models with temperatures of 300 K and 500 K, respectively, of the corresponding specific entropy at 100 bar level in the gas envelope. The Earth and Neptune are also depicted as reference. We include B22 and M22 as references because different results have been published for the same planet, and this refers to Barragán et al. (2022) and El Mufti et al. (2023), respectively. -- astro-ph.EP

We report the discovery, mass, and radius determination of TOI-1801 b, a temperate mini-Neptune around a young M dwarf. TOI-1801 b was observed in TESS sectors 22 and 49, and the alert that this was a TESS planet candidate with a period of 21.3 days went out in April 2020.

However, ground-based follow-up observations, including seeing-limited photometry in and outside transit together with precise radial velocity (RV) measurements with CARMENES and HIRES revealed that the true period of the planet is 10.6 days.

These observations also allowed us to retrieve a mass of 5.74 ± 1.46 M⊕, which together with a radius of 2.08 ± 0.12 R⊕, means that TOI-1801 b is most probably composed of water and rock, with an upper limit of 2\% by mass of H2 in its atmosphere. The stellar rotation period of 16 days is readily detectable in our RV time series and in the ground-based photometry.

We derived a likely age of 600–800 Myr for the parent star TOI-1801, which means that TOI-1801 b is the least massive young mini-Neptune with precise mass and radius determinations. Our results suggest that if TOI-1801 b had a larger atmosphere in the past, it must have been removed by some evolutionary mechanism on timescales shorter than 1 Gyr.

M. Mallorquín, E. Goffo, E. Pallé, N. Lodieu, V. J. S. Béjar, H. Isaacson, M. R. Zapatero Osorio, S. Dreizler, S. Stock, R. Luque, F. Murgas, L. Peña, J. Sanz-Forcada, G. Morello, D. R. Ciardi, E. Furlan, K. A. Collins, E. Herrero, S. Vanaverbeke, P. Plavchan, A. Schweitzer, M. Pérez-Torres, A. Quirrenbach, J. Kemmer, A. P. Hatzes, A. Howard, M. Schlecker, S. Reffert, E. Nagel, J. C. Morales, J. Orell-Miquel, C. Duque-Arribas, I. Carleo, C. Cifuentes, G. Nowak, I. Ribas, A. Reiners, P. J. Amado, J. A. Caballero, Th. Henning, V. Pinter, J. M. Akana Murphy, C. Beard, S. Blunt, C. L. Brinkman, B. Cale, A. Chontos, K. I. Collins, I. J. M. Crossfield, F. Dai, P. A. Dalba, S. Dufoer, M. El Mufti, N. Espinoza, T. Fetherolf, S. Giacalone, C. Gnilka, E. Gonzales, S. K. Grunblatt, S. Howell, D. Huber, S. R. Kane, J. Lubin, M. G. MacDougall, B. Massey, D. Montes, H. Parviainen, V. M. Passegger, A. S. Polanski, P. Robertson, R. P. Schwarz, G. Srdoc, H. M. Tabernero, A. Tanner, E. Turtelboom, J. Van Zandt, L. Weiss, M. Zechmeister

Comments: Accepted in A&A. 29 pages, 21 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2310.10244 [astro-ph.EP] (or arXiv:2310.10244v1 [astro-ph.EP] for this version)
Submission history
From: Manuel Mallorquín Díaz
[v1] Mon, 16 Oct 2023 10:06:01 UTC (16,896 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) 🖖🏻