TOI-1231 b: A Temperate, Neptune-sized Planet Transiting the Nearby M3 Dwarf NLTT 24399

Creators: Burt, Jennifer A.; Dragomir, Diana; Mollière, Paul; Youngblood, Allison; García Muñoz, Antonio; McCann, John; Kreidberg, Laura; Huang, Chelsea X.; Collins, Karen A.; Eastman, Jason D.; Abe, Lyu; Almenara, Jose M.; Crossfield, Ian J. M.; Ziegler, Carl; Rodriguez, Joseph E.; Mamajek, Eric E.; Stassun, Keivan G.; Halverson, Samuel P.; Villanueva, Steven; Butler, R. Paul; Wang, Sharon Xuesong; Schwarz, Richard P.; Ricker, George R.; Vanderspek, Roland; Latham, David W.; Seager, S.; Winn, Joshua N.; Jenkins, Jon M.; Agabi, Abdelkrim; Bonfils, Xavier; Ciardi, David; Cointepas, Marion; Crane, Jeffrey D.; Crouzet, Nicolas; Dransfield, Georgina; Feng, Fabo; Furlan, Elise; Guillot, Tristan; Gupta, Arvind F.; Howell, Steve B.; Jensen, Eric L. N.; Law, Nicholas; Mann, Andrew W.; Marie-Sainte, Wenceslas; Matson, Rachel A.; Matthews, Elisabeth C.; Mékarnia, Djamel; Pepper, Joshua; Scott, Nic; Shectman, Stephen A.; Schlieder, Joshua E.; Schmider, François-Xavier; Stevens, Daniel J.; Teske, Johanna K.; Triaud, Amaury H. M. J.; Charbonneau, David; Berta-Thompson, Zachory K.; Burke, Christopher J.; Daylan, Tansu; Barclay, Thomas; Wohler, Bill; Brasseur, C. E.

Abstract

We report the discovery of a transiting, temperate, Neptune-sized exoplanet orbiting the nearby (d = 27.5 pc), M3V star TOI-1231 (NLTT 24399, L 248-27, 2MASS J10265947-5228099). The planet was detected using photometric data from the Transiting Exoplanet Survey Satellite and followed up with observations from the Las Cumbres Observatory and the Antarctica Search for Transiting ExoPlanets program. Combining the photometric data sets, we find that the newly discovered planet has a radius of 3.65_(-0.15)^(+0.16) R_⊕ and an orbital period of 24.246 days. Radial velocity measurements obtained with the Planet Finder Spectrograph on the Magellan Clay telescope confirm the existence of the planet and lead to a mass measurement of 15.5 ± 3.3 M_⊕. With an equilibrium temperature of just 330 K, TOI-1231 b is one of the coolest small planets accessible for atmospheric studies thus far, and its host star's bright near-infrared brightness (J = 8.88, K_s = 8.07) makes it an exciting target for the Hubble Space Telescope and the James Webb Space Telescope. Future atmospheric observations would enable the first comparative planetology efforts in the 250–350 K temperature regime via comparisons with K2-18 b. Furthermore, TOI-1231's high systemic radial velocity (70.5 km s⁻¹) may allow for the detection of low-velocity hydrogen atoms escaping the planet by Doppler, shifting the H i Lyα stellar emission away from the geocoronal and interstellar medium absorption features.

Additional Information

© 2021. The American Astronomical Society. Received 2020 November 18; revised 2021 May 13; accepted 2021 May 20; published 2021 August 3. This paper includes data collected by the TESS mission. Funding for the TESS mission is provided by NASA's Science Mission directorate. We acknowledge the use of public TESS alert data from pipelines at the TESS Science Office and the TESS Science Operations Center. This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile. This work makes use of observations from the LCOGT network and from the ASTEP telescope. ASTEP benefited from the support of the French and Italian polar agencies IPEV and PNRA in the framework of the Concordia Station program. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Some of the observations in the paper made use of the high-resolution-imaging instrument Zorro. 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. Zorro was mounted on the Gemini-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). 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. Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX13AC07G and by other grants and contracts. 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 has made use of NASA's Astrophysics Data System. This research has also 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. This research made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013). Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA). D.D. acknowledges support from the TESS Guest Investigator Program grant 80NSSC19K1727 and NASA Exoplanet Research Program grant 18-2XRP18_2-0136. TD acknowledges support from MIT's Kavli Institute as a Kavli postdoctoral fellow. E.M. acknowledges support from NASA award 17-K2G06-0030. P.M. acknowledges support from the European Research Council under the European Union's Horizon 2020 research and innovation program under grant agreement No. 832428. T.G., A.A., L.A., D.M., F.-X.S. acknowledge support from Idex UCAJEDI (ANR-15-IDEX-01). D.J.S. acknowledges funding support from the Eberly Research Fellowship from The Pennsylvania State University Eberly College of Science. The Center for Exoplanets and Habitable Worlds is supported by the Pennsylvania State University, the Eberly College of Science, and the Pennsylvania Space Grant Consortium. This research received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No. 803193/BEBOP), and from the Science and Technology Facilities Council (STFC; grant No. ST/S00193X/1). This publication makes use of VOSA, developed under the Spanish Virtual Observatory project supported by the Spanish MINECO through grant AyA2017-84089. VOSA has been partially updated by using funding from the European Union's Horizon 2020 Research and Innovation Programme, under grant agreement no 776403 (EXOPLANETS-A). Facilities: TESS - , Magellan: Clay (Planet Finder Spectrograph) - , Gemini-South (Zorro) - , SOAR - , LCOGT - , ASTEP. - Software: AstroImageJ (Collins et al. 2017), TAPIR (Jensen 2013), EXOFASTv2 (Eastman et al. 2019), petitCODE (Mollière et al. 2017), PyMultiNest (Buchner 2016), MultiNest (Feroz et al. 2009), Astropy (Astropy Collaboration et al. 2013).

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