Issue |
A&A
Volume 653, September 2021
|
|
---|---|---|
Article Number | A97 | |
Number of page(s) | 17 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361/202141277 | |
Published online | 13 September 2021 |
A large sub-Neptune transiting the thick-disk M4 V TOI-2406
1
Center for Space and Habitability, University of Bern,
Gesellschaftsstrasse 6,
3012
Bern,
Switzerland
e-mail: robert.wells@csh.unibe.ch
2
Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology,
77 Massachusetts Avenue,
Cambridge,
MA
02139,
USA
3
Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology,
Cambridge,
MA 02139,
USA
4
Universidad Nacional de Córdoba – Observatorio Astronómico de Córdoba,
Laprida 854, X5000BGR,
Córdoba,
Argentina
5
Consejo Nacional de Investigaciones Cientf́icas y Técnicas (CONICET),
Buenos Aires,
Argentina
6
Universidad Nacional Autónoma de México, Instituto de Astronomía,
AP 70-264,
CDMX
04510,
México
7
Center for Astrophysics and Space Science, University of California San Diego,
La Jolla,
CA 92093,
USA
8
Max Planck Institute for Astronomy (MPIA),
Koenigstuhl 17,
69117
Heidelberg,
Germany
9
Astrobiology Research Unit, Université de Liège,
Allée du 6 Août 19C,
4000
Liège,
Belgium
10
Space Sciences, Technologies and Astrophysics Research (STAR) Institute, Universitďe Liège, Allée du 6 Août 19C,
4000
Liège,
Belgium
11
Department of Physics, Massachusetts Institute of Technology,
Cambridge,
MA 02139,
USA
12
Universidad Nacional Autónoma de México, Instituto de Astronomía,
AP 106,
Ensenada
22800,
BC,
México
13
Department of Physics & Astronomy, Vanderbilt University,
6301 Stevenson Center Ln.,
Nashville,
TN 37235,
USA
14
NASA Ames Research Center,
Moffett Field,
CA 94035,
USA
15
School of Physics & Astronomy, University of Birmingham,
Edgbaston,
Birmimgham
B15 2TT,
UK
16
Steward Observatory, The University of Arizona,
933 N. Cherry Avenue,
Tucson,
AZ 85721,
USA
17
Lunar and Planetary Laboratory, The University of Arizona, 1639 E. University Boulevard,
Tucson,
AZ 85721,
USA
18
Oukaimeden Observatory, High Energy Physics and Astrophysics Laboratory, Cadi Ayyad University,
Marrakech,
Morocco
19
Graduate Institute of Astronomy, National Central University,
300 Jhongda Road,
Zhongli,
Taoyuan
32001,
Taiwan
20
Instituto de Astrofísica de Canarias (IAC),
Calle Vía Láctea s/n,
38200
La Laguna,
Tenerife,
Spain
21
Center for Astrophysics, Harvard & Smithsonian,
60 Garden Street,
Cambridge,
MA,
02138,
USA
22
Dpto. Física Teórica y del Cosmos, Universidad de Granada,
18071,
Granada,
Spain
23
NASA Exoplanet Science Institute, Caltech/IPAC,
Mail Code 100-22, 1200 E. California Blvd.,
Pasadena,
CA 91125,
USA
24
Vatican Observatory Research Group, University of Arizona,
933 N Cherry Ave.,
Tucson AZ,
85721-0065,
USA
25
Department of Astronomy, Tsinghua University,
Beijing
100084,
PR China
26
Department of Astronomy, 501 Campbell Hall, University of California at Berkeley,
Berkeley,
CA,
94720,
USA
27
Department of Physics & Astronomy, University of California, Los Angeles,
Los Angeles,
CA 90095,
USA
28
Department of Physics, University of Warwick,
Coventry,
CV4 7AL,
UK
29
Cavendish Laboratory,
JJ Thomson Avenue,
Cambridge,
CB3 0HE,
UK
30
Space Telescope Science Institute,
3700 San Martin Drive,
Baltimore,
MD,
21218,
USA
31
Patashnick Voorheesville Observatory,
Voorheesville,
NY 12186,
USA
32
Department of Aeronautics and Astronautics, MIT,
77 Massachusetts Avenue,
Cambridge,
MA 02139,
USA
33
SETI Institute,
Mountain View,
CA 94043,
USA
34
Department of Astrophysical Sciences, Princeton University,
4 Ivy Lane,
Princeton,
NJ 08544,
USA
Received:
10
May
2021
Accepted:
23
July
2021
Context. Large sub-Neptunes are uncommon around the coolest stars in the Galaxy and are rarer still around those that are metal-poor. However, owing to the large planet-to-star radius ratio, these planets are highly suitable for atmospheric study via transmission spectroscopy in the infrared, such as with JWST.
Aims. Here we report the discovery and validation of a sub-Neptune orbiting the thick-disk, mid-M dwarf star TOI-2406. The star’s low metallicity and the relatively large size and short period of the planet make TOI-2406 b an unusual outcome of planet formation, and its characterisation provides an important observational constraint for formation models.
Methods. We first infer properties of the host star by analysing the star’s near-infrared spectrum, spectral energy distribution, and Gaia parallax. We use multi-band photometry to confirm that the transit event is on-target and achromatic, and we statistically validate the TESS signal as a transiting exoplanet. We then determine physical properties of the planet through global transit modelling of the TESS and ground-based time-series data.
Results. We determine the host to be a metal-poor M4 V star, located at a distance of 56 pc, with properties Teff = 3100 ± 75 K, M* = 0.162 ± 0.008M⊙, R* = 0.202 ± 0.011R⊙, and [Fe∕H] = −0.38 ± 0.07, and a member of the thick disk. The planet is a relatively large sub-Neptune for the M-dwarf planet population, with Rp = 2.94 ± 0.17R⊕ and P= 3.077 d, producing transits of 2% depth. We note the orbit has a non-zero eccentricity to 3σ, prompting questions about the dynamical history of the system.
Conclusions. This system is an interesting outcome of planet formation and presents a benchmark for large-planet formation around metal-poor, low-mass stars. The system warrants further study, in particular radial velocity follow-up to determine the planet mass and constrain possible bound companions. Furthermore, TOI-2406 b is a good target for future atmospheric study through transmission spectroscopy. Although the planet’s mass remains to be constrained, we estimate the S/N using amass-radius relationship, ranking the system fifth in the population of large sub-Neptunes, with TOI-2406 b having a much lower equilibrium temperature than other spectroscopically accessible members of this population.
Key words: planets and satellites: detection / stars: individual: TOI-2406 / techniques: photometric
© ESO 2021
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