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

Burt, Jennifer A. and Dragomir, Diana and Molliere, Paul and Youngblood, Allison and Munoz, Antonio Garcia and McCann, John and Kreidberg, Laura and Huang, Chelsea X. ORCID: and Collins, Karen A. and Eastman, Jason D. and Abe, Lyu and Almenara, Jose M. and Crossfield, Ian J. M. and Ziegler, Carl and Rodriguez, Joseph E. and Mamajek, Eric E. and Stassun, Keivan G. and Halverson, Samuel P. and Villanueva, Steven and Butler, R. Paul and Wang, Sharon Xuesong and Schwarz, Richard P. and Ricker, George R. and Vanderspek, Roland and Latham, David W. and Seager, S. and Winn, Joshua N. and Jenkins, Jon M. and Agabi, Abdelkrim and Bonfils, Xavier and Ciardi, David and Cointepas, Marion and Crane, Jeffrey D. and Crouzet, Nicolas and Dransfield, Georgina and Feng, Fabo and Furlan, Elise and Guillot, Tristan and Gupta, Arvind F. and Howell, Steve B. and Jensen, Eric L. N. and Law, Nicholas and Mann, Andrew W. and Marie-Sainte, Wenceslas and Matson, Rachel A. and Matthews, Elisabeth C. and Mekarnia, Djamel and Pepper, Joshua and Scott, Nic and Shectman, Stephen A. and Schlieder, Joshua E. and Schmider, Francois-Xavier and Stevens, Daniel J. and Teske, Johanna K. and Triaud, Amaury H. M. J. and Charbonneau, David and Berta-Thompson, Zachory K. and Burke, Christopher J. and Daylan, Tansu and Barclay, Thomas and Wohler, Bill and Brasseur, C. E. (2021) TOI-1231 b: A Temperate, Neptune-sized Planet Transiting the Nearby M3 Dwarf NLTT 24399. The Astronomical Journal, 162 (3):87. pp. 1-15. ISSN 0004-6256

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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}_{\oplus } 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, Ks = 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.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Published version deposited in accordance with the copyright policy of the publisher.
Faculty/School / Institute/Centre: No Faculty
Faculty/School / Institute/Centre: No Faculty
Date Deposited: 04 Apr 2022 00:07
Last Modified: 24 May 2022 05:02
Uncontrolled Keywords: Exoplanet astronomy (486); Transit photometry (1709); Radial velocity (1332); Mini Neptunes (1063); Astrophysics - Earth and Planetary Astrophysics
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510109 Stellar astronomy and planetary systems
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