TOI-2257 b: A highly eccentric long-period sub-Neptune transiting a nearby M dwarf
Metadatos
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EDP
Materia
Planets and satellites: detection Stars: individual: TOI-2257 Stars: individual: TIC 198485881 Techniques: photometric
Date
2022-01-07Referencia bibliográfica
Schanche, N... [et al.]. TOI-2257 b: A highly eccentric long-period sub-Neptune transiting a nearby M dwarf. A&A, 657 (2022) A45 DOI: [https://doi.org/10.1051/0004-6361/202142280]
Patrocinador
Swiss National Science Foundation (SNSF); European Commission PP00P2-163967 PP00P2-190080; MIT's Kavli Institute; European Space Agency European Commission; Ministry of Science and Higher Education of the Russian Federation 075-15-2020-780 (N13.1902.21.0039); Heising-Simons Foundation; French Community of Belgium; DGAPA; Programa de Apoyo a Proyectos de Investigacion e Innovacion Tecnologica (PAPIIT) Universidad Nacional Autonoma de Mexico BG-101321; TESS Guest Investigator Program 80NSSC19K1727; NASA Exoplanet Research Program 18-2XRP18_2-0136; Centre for Space and Habitability (CSH) of the University of Bern; Swiss National Science Foundation (SNSF); European Research Council (ERC) 336480; Actions de Recherche Concertee (ARC) grant - Wallonia-Brussels Federation; UK Research & Innovation (UKRI); Science & Technology Facilities Council (STFC); Science and Technology Development Fund (STDF) ST/S00193X/1; Fonds de la Recherche Scientifique - FNRS T010920F; Simons Foundation 327127; MERAC foundation; Fonds de la Recherche Scientifique - FNRS PDR T.0120.21; Swiss National Science Foundation (SNSF); National Science Foundation (NSF); NASA Exoplanet Exploration Program NASA's Science Mission Directorate; European Research Council (ERC) 679030 803193/BEBOP; Balzan Prize Foundation BEL-SPO/BRAIN2.0 research program (PORTAL project)Résumé
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 similar to 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-circle plus 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 (similar to 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.