Issue |
A&A
Volume 657, January 2022
|
|
---|---|---|
Article Number | A45 | |
Number of page(s) | 18 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361/202142280 | |
Published online | 07 January 2022 |
TOI-2257 b: A highly eccentric long-period sub-Neptune transiting a nearby M dwarf
1
Center for Space and Habitability, University of Bern,
Gesellschaftsstrasse 6,
3012
Bern,
Switzerland
e-mail: nicole.schanche@unibe.ch
2
Astrobiology Research Unit, Université de Liège,
Allée du 6 Août 19C,
4000
Liège,
Belgium
3
Space Sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège,
Allée du 6 Août 19C,
4000
Liège,
Belgium
4
Department of Physics, and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology (MIT),
Cambridge,
MA
02139,
USA
5
European Space Agency (ESA), European Space Research and Technology Centre (ESTEC),
Keplerlaan 1,
2201
AZ Noordwijk,
The Netherlands
6
Center for Astrophysics and Space Science, University of California San Diego,
La Jolla,
CA
92093,
USA
7
Instituto de Astrofísica de Canarias (IAC),
Calle Vía Láctea s/n,
38200
La Laguna,
Tenerife,
Spain
8
Universidad Nacional Autónoma de México, Instituto de Astronomía,
AP 70-264,
CDMX
04510,
Mexico
9
Universidad Nacional de Córdoba - Observatorio Astronómico de Córdoba,
Laprida 854,
X5000BGR,
Córdoba,
Argentina
10
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET),
Argentina
11
Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology,
77 Massachusetts Avenue,
Cambridge,
MA
02139,
USA
12
School of Physics & Astronomy, University of Birmingham,
Edgbaston,
Birmimgham
B15 2TT,
UK
13
Department of Physics & Astronomy, Vanderbilt University,
6301 Stevenson Center Ln.,
Nashville,
TN
37235,
USA
14
Jet Propulsion Laboratory, California Institute of Technology,
4800 Oak Grove Drive, MS 169-224,
Pasadena,
CA
91109,
USA
15
Oukaimeden Observatory, High Energy Physics and Astrophysics Laboratory, Cadi Ayyad University,
Marrakech,
Morocco
16
Sternberg Astronomical Institute, Moscow State University (SAI MSU),
Universitetskii pr. 13,
Moscow
119991,
Russia
17
Physikalisches Institut, University of Bern,
Gesellsschaftstrasse 6,
3012
Bern,
Switzerland
18
Center for Astrophysics | Harvard & Smithsonian,
60 Garden Street,
Cambridge,
MA,
02138,
USA
19
Observatoire de l’Université de Genève,
Chemin des Maillettes 51,
1290
Versoix,
Switzerland
20
Caltech/IPAC,
1200 E. California Boulevard,
Pasadena,
CA
91125,
USA
21
Dpto. Física Teórica y del Cosmos, Universidad de Granada,
18071
Granada,
Spain
22
Department of Physics and Astronomy, University of New Mexico,
1919 Lomas Blvd NE,
Albuquerque,
NM
87131,
USA
23
NASA Exoplanet Science Institute, Caltech/IPAC,
Mail Code 100-22, 1200 E. California Blvd.,
Pasadena,
CA
91125,
USA
24
NASA Ames Research Center,
Moffett Field,
CA
94035,
USA
25
Universidad Nacional Autónoma de México, Instituto de Astronomía,
AP 106,
Ensenada
22800,
BC,
Mexico
26
Department of Astronomy, University of Florida,
Gainesville,
FL,
32611,
USA
27
Department of Physics, University of Warwick,
Gibbet Hill Road,
Coventry
CV4 7AL,
UK
28
Dept. of Physics & Astronomy,
Swarthmore College,
Swarthmore
PA
19081,
USA
29
Department of Astronomy, Wellesley College,
Wellesley,
MA
02481,
USA
30
Cavendish Laboratory,
JJ Thomson Avenue,
Cambridge,
CB3 0HE,
UK
31
NASA Goddard Space Flight Center,
8800 Greenbelt Road,
Greenbelt,
MD
20771,
USA
32
Department of Aeronautics and Astronautics,
MIT, 77 Massachusetts Avenue,
Cambridge,
MA
02139,
USA
33
Department of Astrophysical Sciences, Princeton University,
4 Ivy Lane,
Princeton,
NJ
08544,
USA
Received:
22
September
2021
Accepted:
28
October
2021
Context. Thanks to the relative ease of finding and characterizing small planets around M-dwarf stars, these objects have become cornerstones in the field of exoplanet studies. The current paucity of planets in long-period orbits around M dwarfs makes such objects particularly compelling as they provide clues about the formation and evolution of these systems.
Aims. In this study we present the discovery of TOI-2257 b (TIC 198485881), a long-period (35 d) sub-Neptune orbiting an M3 star at 57.8 pc. Its transit depth is about 0.4%, large enough to be detected with medium-size, ground-based telescopes. The long transit duration suggests the planet is in a highly eccentric orbit (e ~ 0.5), which would make it the most eccentric planet known to be transiting an M-dwarf star.
Methods. We combined TESS and ground-based data obtained with the 1.0-meter SAINT-EX, 0.60-meter TRAPPIST-North, and 1.2-meter FLWO telescopes to find a planetary size of 2.2 R⊕ and an orbital period of 35.19 days. In addition, we make use of archival data, high-resolution imaging, and vetting packages to support our planetary interpretation.
Results. With its long period and high eccentricity, TOI-2257 b falls into a novel slice of parameter space. Despite the planet’s low equilibrium temperature (~256 K), its host star’s small size (R* = 0.311 ± 0.015) and relative infrared brightness (Kmag = 10.7) make it a suitable candidate for atmospheric exploration via transmission spectroscopy.
Key words: planets and satellites: detection / stars: individual: TOI-2257 / stars: individual: TIC 198485881 / techniques: photometric
© ESO 2022
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