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TOI-2257 b: A highly eccentric long-period sub-Neptune transiting a nearby M dwarf

Schanche, N. and Pozuelos, F. J. and Günther, M. N. and Wells, R. D. and Burgasser, A. J. and Chinchilla, P. and Delrez, L. and Ducrot, E. and Garcia, L. J. and Gómez Maqueo Chew, Y. and Jofré, E. and Rackham, B. V. and Sebastian, D. and Stassun, K. G. and Stern, D. and Timmermans, M. and Barkaoui, K. and Belinski, A. and Benkhaldoun, Z. and Benz, W. and Bieryla, A. and Bouchy, F. and Burdanov, A. and Charbonneau, D. and Christiansen, J. L. and Collins, K. A. and Demory, B.-O. and Dévora-Pajares, M. and de Wit, J. and Dragomir, D. and Dransfield, G. and Furlan, E. and Ghachoui, M. and Gillon, M. and Gnilka, C. and Gómez-Muñoz, M. A. and Guerrero, N. and Harris, M. and Heng, K. and Henze, C. E. and Hesse, K. and Howell, S. B. and Jehin, E. and Jenkins, J. and Jensen, E. L. N. and Kunimoto, M. and Latham, D. W. and Lester, K. and McLeod, K. K. and Mireles, I. and Murray, C. A. and Niraula, P. and Pedersen, P. P. and Queloz, D. and Quintana, E. V. and Ricker, G. and Rudat, A. and Sabin, L. and Safonov, B. and Schroffenegger, U. and Scott, N. and Seager, S. and Strakhov, I. and Triaud, A. H. M. J. and Vanderspek, R. and Vezie, M. and Winn, J. (2022) TOI-2257 b: A highly eccentric long-period sub-Neptune transiting a nearby M dwarf. Astronomy and Astrophysics, 657 . Art. No. A45. ISSN 0004-6361. doi:10.1051/0004-6361/202142280.

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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 (K_(mag) = 10.7) make it a suitable candidate for atmospheric exploration via transmission spectroscopy.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Schanche, N.0000-0002-9526-3780
Pozuelos, F. J.0000-0003-1572-7707
Günther, M. N.0000-0002-3164-9086
Wells, R. D.0000-0002-7240-8473
Burgasser, A. J.0000-0002-6523-9536
Delrez, L.0000-0001-6108-4808
Ducrot, E.0000-0002-7008-6888
Stassun, K. G.0000-0002-3481-9052
Stern, D.0000-0003-2686-9241
Barkaoui, K.0000-0003-1464-9276
Benkhaldoun, Z.0000-0001-6285-9847
Bieryla, A.0000-0001-6637-5401
Bouchy, F.0000-0002-7613-393X
Charbonneau, D.0000-0002-9003-484X
Christiansen, J. L.0000-0002-8035-4778
Collins, K. A.0000-0001-6588-9574
Demory, B.-O.0000-0002-9355-5165
de Wit, J.0000-0003-2415-2191
Dragomir, D.0000-0003-2313-467X
Furlan, E.0000-0001-9800-6248
Gillon, M.0000-0003-1462-7739
Gnilka, C.0000-0003-2519-6161
Howell, S. B.0000-0002-2532-2853
Jehin, E.0000-0001-8923-488X
Jensen, E. L. N.0000-0002-4625-7333
Latham, D. W.0000-0001-9911-7388
Queloz, D.0000-0002-3012-0316
Ricker, G.0000-0003-2058-6662
Seager, S.0000-0002-6892-6948
Triaud, A. H. M. J.0000-0002-5510-8751
Vanderspek, R.0000-0001-6763-6562
Winn, J.0000-0002-4265-047X
Additional Information:© ESO 2022. Received 22 September 2021; Accepted 28 October 2021. Published online 07 January 2022. N.S., R.W. and B.-O.D. acknowledge support from the Swiss National Science Foundation (PP00P2-163967 and PP00P2-190080). M.N.G. acknowledges support from MIT’s Kavli Institute as a Juan Carlos Torres Fellow and from the European Space Agency (ESA) as an ESA Research Fellow. A.A.B., B.S.S.and I.A.S. acknowledge the support of the Ministry of Science and Higher Education of the Russian Federation under the grant 075-15-2020-780 (N13.1902.21.0039). L.D. is an F.R.S.-FNRS Postdoctoral Researcher. B.V.R. thanks the Heising-Simons Foundation for support. This publication benefits from the support of the French Community of Belgium in the context of the FRIA Doctoral Grant awarded to M.T. and E.J. acknowledges DGAPA for his postdoctoral fellowship. Y.G.M.C. acknowledges support from UNAM-DGAPA PAPIIT BG-101321. D.D. acknowledges support from the TESS Guest Investigator Program grant 80NSSC19K1727 and NASA Exoplanet Research Program grant 18-2XRP18_2-0136. We acknowledge support from the Centre for Space and Habitability (CSH) of the University of Bern. Part of this work received support from the National Centre for Competence in Research PlanetS, supported by the Swiss National Science Foundation (SNSF). Funding for the TESS mission is provided by NASA’s Science Mission Directorate. We acknowledge the use of public TESS data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. This research has made use of the Exoplanet Follow-up Observation Program website, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. This paper includes data collected by the TESS mission that are publicly available from the Mikulski Archive for Space Telescopes (MAST). This work is based upon observations carried out at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir (OAN-SPM), Baja California, México. We warmly thank the entire technical staff of the Observatorio Astronómico Nacional at San Pedro Mártir in México for their unfailing support to SAINT-EX operations, namely: E. Cadena, T. Calvario, E. Colorado, F. Díaz, A. Franco, B. García, C. Guerrero, G. Guisa, F. Guillen, A. Landa, L. Figueroa, B. Hernández, J. Herrera, E. López, E. Lugo, B. Martínez, G. Melgoza, F. Montalvo, J.M. Nuñez, J.L. Ochoa, I. Plauchu, F. Quiroz, H. Riesgo, H. Serrano, T. Verdugo, I. Zavala. The research leading to these results has received funding from the European Research Council (ERC) under the FP/2007–2013 ERC grant agreement n° 336480, and under the European Union’s Horizon 2020 research and innovation programme (grants agreements n° 679030 and 803193/BEBOP); from an Actions de Recherche Concertée (ARC) grant, financed by the Wallonia–Brussels Federation, from the Balzan Prize Foundation, from the BELSPO/BRAIN2.0 research program (PORTAL project), from the Science and Technology Facilities Council (STFC; grant n° ST/S00193X/1), and from F.R.S-FNRS (Research Project ID T010920F). This work was also partially supported by a grant from the Simons Foundation (PI: Queloz, grant number 327127), as well as by the MERAC foundation (PI: Triaud). PI:Gillon is F.R.S.-FNRS Senior Research Associate. TRAPPIST is funded by the Belgian Fund for Scientific Research (Fond National de la Recherche Scientifique, FNRS) under the grant PDR T.0120.21, with the participation of the Swiss National Science Fundation (SNF). M.G. and E.J. are F.R.S.-FNRS Senior Research Associate. This work makes use of observations from the LCOGT network. Part of the LCOGT telescope time was granted by NOIRLab through the Mid-Scale Innovations Program (MSIP). M.S.I.P. is funded by NSF. Some of the observations in the paper made use of the High-Resolution Imaging instrument(s) ‘Alopeke (and/or Zorro). ‘Alopeke (and/or Zorro) was funded by the NASA Exoplanet Exploration Program and built at the NASA Ames Research Center by Steve B. Howell, Nic Scott, Elliott P. Horch, and Emmett Quigley. Data were reduced using a software pipeline originally written by Elliott Horch and Mark Everett. ‘Alopeke (and/or Zorro) was mounted on the Gemini North (and/or South) telescope of the international Gemini Observatory, a program of NSF’s OIR Lab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation, on behalf of the Gemini partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. This research made use of exoplanet (Foreman-Mackey et al. 2021a,b) and its dependencies (Agol et al. 2020; Kumar et al. 2019; Astropy Collaboration 2013, 2018; Kipping 2013; Luger et al. 2019; Salvatier et al. 2016; Theano Development Team 2016). Additional use of software packages AstroImageJ (Collins et al. 2017) and TAPIR (Jensen 2013).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Swiss National Science Foundation (SNSF)PP00P2-163967
Swiss National Science Foundation (SNSF)PP00P2-190080
Kavli Institute for Cosmological PhysicsUNSPECIFIED
European Space Agency (ESA)UNSPECIFIED
Ministry of Science and Higher Education of the Russian Federation075-15-2020-780
Ministry of Science and Higher Education of the Russian FederationN13.1902.21.0039
Heising-Simons FoundationUNSPECIFIED
Fund for Research Training in Industry and Agriculture (FRIA)UNSPECIFIED
Dirección General Asuntos del Personal (DGAPA)UNSPECIFIED
Universidad Nacional Autónoma de México (UNAM)BG-101321
University of BernUNSPECIFIED
European Research Council (ERC)336480
European Research Council (ERC)679030
European Research Council (ERC)803193
Actions de Recherche Concertées (ARC)UNSPECIFIED
Wallonia-Brussels FederationUNSPECIFIED
Balzan Prize FoundationUNSPECIFIED
Belgian Federal Science Policy Office (BELSPO)UNSPECIFIED
Science and Technology Facilities Council (STFC)ST/S00193X/1
Fonds de la Recherche Scientifique (FNRS)T010920F
Simons Foundation327127
Fond National de la Recherche scientifique de Belgique (FNRS)PDR T.0120.21
Subject Keywords:planets and satellites: detection – stars: individual: TOI-2257 – stars: individual: TIC 198485881 – techniques: photometric
Record Number:CaltechAUTHORS:20220131-740965700
Persistent URL:
Official Citation:TOI-2257 b: A highly eccentric long-period sub-Neptune transiting a nearby M dwarf. N. Schanche, F. J. Pozuelos, M. N. Günther, R. D. Wells, A. J. Burgasser, P. Chinchilla, L. Delrez, E. Ducrot, L. J. Garcia, Y. Gómez Maqueo Chew, E. Jofré, B. V. Rackham, D. Sebastian, K. G. Stassun, D. Stern, M. Timmermans, K. Barkaoui, A. Belinski, Z. Benkhaldoun, W. Benz, A. Bieryla, F. Bouchy, A. Burdanov, D. Charbonneau, J. L. Christiansen, K. A. Collins, B.-O. Demory, M. Dévora-Pajares, J. de Wit, D. Dragomir, G. Dransfield, E. Furlan, M. Ghachoui, M. Gillon, C. Gnilka, M. A. Gómez-Muñoz, N. Guerrero, M. Harris, K. Heng, C. E. Henze, K. Hesse, S. B. Howell, E. Jehin, J. Jenkins, E. L. N. Jensen, M. Kunimoto, D. W. Latham, K. Lester, K. K. McLeod, I. Mireles, C. A. Murray, P. Niraula, P. P. Pedersen, D. Queloz, E. V. Quintana, G. Ricker, A. Rudat, L. Sabin, B. Safonov, U. Schroffenegger, N. Scott, S. Seager, I. Strakhov, A. H. M. J. Triaud, R. Vanderspek, M. Vezie and J. Winn. A&A, 657 (2022) A45; DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113187
Deposited By: Tony Diaz
Deposited On:01 Feb 2022 18:26
Last Modified:01 Feb 2022 18:26

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