Issue |
A&A
Volume 692, December 2024
|
|
---|---|---|
Article Number | A238 | |
Number of page(s) | 22 | |
Section | Planets, planetary systems, and small bodies | |
DOI | https://doi.org/10.1051/0004-6361/202452244 | |
Published online | 18 December 2024 |
Characterisation of TOI-406 as a showcase of the THIRSTEE program
A two-planet system straddling the M-dwarf density gap
1
Instituto de Astrofísica de Canarias (IAC),
38205
La Laguna,
Tenerife,
Spain
2
Departamento de Astrofísica, Universidad de La Laguna (ULL),
38206
La Laguna,
Tenerife,
Spain
3
Department of Astronomy and Astrophysics, University of Chicago,
Chicago,
IL
60637,
USA
4
Institut Trottier de recherche sur les exoplanètes, Département de Physique, Université de Montréal,
Montréal,
Québec,
Canada
5
Department of Astronomy and Astrophysics, University of California,
Santa Cruz,
CA
95064,
USA
6
Centro de Astrobiología (CSIC-INTA),
Crta. Ajalvir km 4,
28850
Torrejón de Ardoz, Madrid,
Spain
7
Departamento de Física de la Tierra y Astrofísica & IPARCOS-UCM (Instituto de Física de Partículas y del Cosmos de la UCM), Facultad de Ciencias Físicas, Universidad Complutense de Madrid,
28040
Madrid,
Spain
8
Center for Astrophysics | Harvard & Smithsonian,
60 Garden Street,
Cambridge,
MA
02138,
USA
9
Observatoire du Mont-Mégantic, Université de Montréal,
C.P. 6128, Succ. Centre-ville,
Montréal
H3C 3J7,
Québec,
Canada
10
Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University,
Grudziadzka 5,
87–100
Toruń,
Poland
11
Observatoire de Genève, Département d’Astronomie, Université de Genève,
Chemin Pegasi 51b,
1290
Versoix,
Switzerland
12
Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, Campus Universitário,
Natal,
RN 59072-970,
Brazil
13
INAF – Osservatorio Astrofisico di Arcetri,
Largo E. Fermi 5,
Florence,
Italy
14
INAF – Osservatorio Astrofisico di Torino,
Via Osservatorio 20,
10025
Pino Torinese,
Italy
15
University of Grenoble Alpes, CNRS, IPAG,
F-38000
Grenoble,
France
16
American Association of Variable Star Observers,
185 Alewife Brook Parkway, Suite 410,
Cambridge,
MA
02138,
USA
17
Department of Physics & Astronomy, University of Kansas,
1082 Malott, 1251 Wescoe Hall Drive,
Lawrence,
KS 66045,
USA
18
The Maury Lewin Astronomical Observatory,
Glendora,
CA
91741,
USA
19
Light Bridges S.L., Observatorio del Teide,
Carretera del Observatorio, s/n Guimar,
38500
Tenerife,
Canarias,
Spain
20
University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München,
Scheinerstr. 1,
81679
Munich,
Germany
21
European Southern Observatory (ESO),
Karl-Schwarzschild-Str. 2,
85748
Garching bei München,
Germany
22
Kotizarovci Observatory,
Sarsoni 90,
51216
Viskovo,
Croatia
23
Mullard Space Science Laboratory, University College London,
Surrey,
UK
★ Corresponding author; glacedelli@iac.es
Received:
13
September
2024
Accepted:
2
November
2024
Context. The exoplanet sub-Neptune population currently poses a conundrum, as to whether small-size planets are volatile-rich cores without an atmosphere, or rocky cores surrounded by a H-He envelope. To test the different hypotheses from an observational point of view, a large sample of small-size planets with precise mass and radius measurements is the first necessary step. On top of that, much more information will likely be needed, including atmospheric characterisation and a demographic perspective on their bulk properties.
Aims. We present here the concept and strategy of the THIRSTEE project, which aims to shed light on the composition of the sub-Neptune population across stellar types by increasing their number and improving the accuracy of bulk density measurements, as well as investigating their atmospheres and performing statistical, demographic analysis. We report the first results of the program, characterising a new two-planet system around the M-dwarf TOI-406.
Methods. We analysed TESS and ground-based photometry together with high-precision ESPRESSO and NIRPS/HARPS radial velocities to derive the orbital parameters and investigate the internal composition of the two planets orbiting TOI-406.
Results. TOI-406 hosts two planets with radii and masses of Rc = 1.32 ± 0.12 R⊕, Mc = 2.08−0.22+0.23 M⊕ and Rb = 2.08−0.15+0.16 R⊕, Mb = 6.57−0.90+1.00 M⊕, orbiting with periods of 3.3 and 13.2 days, respectively. The inner planet is consistent with an Earth-like composition, while the external one is compatible with multiple internal composition models, including volatile-rich planets without H/He atmospheres. The two planets are located in two distinct regions in the mass-density diagram, supporting the existence of a density gap among small exoplanets around M dwarfs. With an equilibrium temperature of only Teq = 368 K, TOI-406 b stands up as a particularly interesting target for atmospheric characterisation with JWST in the low-temperature regime.
Key words: planets and satellites: composition / planets and satellites: detection / planets and satellites: individual: TOI-406
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article is published in open access under the Subscribe to Open model. Subscribe to A&A to support open access publication.
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.