GJ 238 b: A 0.57 Earth Radius Planet Orbiting an M2.5 Dwarf Star at 15.2 pc

Creators: Tey, Evan; Shporer, Avi; Lin, Zifan; Stassun, Keivan G.; Lissauer, Jack J.; Hellier, Coel; Collins, Karen A.; Collins, Kevin I.; Wingham, Geof; Relles, Howard M.; Mallia, Franco; Isopi, Giovanni; Kielkopf, John F.; Conti, Dennis M.; Schwarz, Richard P.; Zapparata, Aldo; Giacalone, Steven; Furlan, Elise; Hartman, Zachary D.; Howell, Steve B.; Scott, Nicholas J.; Ziegler, Carl; Briceño, César; Law, Nicholas; Mann, Andrew W.; Charbonneau, David; Essack, Zahra; Striegel, Stephanie; Ricker, George R.; Vanderspek, Roland; Seager, Sara; Winn, Joshua N.; Jenkins, Jon M.

Abstract

We report the discovery of the transiting planet GJ 238 b, with a radius of 0.566 ± 0.014 R_⊕ (1.064 ± 0.026 times the radius of Mars) and an orbital period of 1.74 days. The transit signal was detected by the TESS mission and designated TOI-486.01. The star's position close to the southern ecliptic pole allows for almost continuous observations by TESS when it is observing the southern sky. The host star is an M2.5 dwarf with V = 11.57 ± 0.02 mag, K = 7.030 ± 0.023 mag, a distance of 15.2156 ± 0.0030 pc, a mass of 0.4193_(−0.0098)^(+0.0095) M_☉, a radius of 0.4314_(−0.0071)^(+0.0075) R_☉, and an effective temperature of 3485 ± 140 K. We validate the planet candidate by ruling out or rendering highly unlikely each of the false positive scenarios, based on archival data and ground-based follow-up observations. Validation was facilitated by the host star's small size and high proper motion of 892.633 ± 0.025 mas yr^–1.

Copyright and License

© 2024. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

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 paper includes data collected by the TESS mission, which are publicly available from the Mikulski Archive for Space Telescopes (MAST). 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 research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with NASA under the Exoplanet Exploration Program. The Digitized Sky Surveys were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. The plates were processed into the present compressed digital form with the permission of these institutions. 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). MSIP is funded by NSF. Based in part on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia e Inovações (MCTI/LNA) do Brasil, the US National Science Foundation's NOIRLab, the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU). Some of the observations in this paper made use of the High-Resolution Imaging instrument Zorro and were obtained under Gemini LLP proposal number GN/S-2021A-LP-105. 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). 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. Z.L. acknowledges funding from the Center for Matter at Atomic Pressures (CMAP), a National Science Foundation (NSF) Physics Frontiers Center, under Award PHY-2020249. K.A.C. acknowledges support from the TESS mission via subaward s3449 from MIT. S.G. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-2303922.

Facilities

ESO:3.6 m (HARPS) - , Exoplanet Archive - , Gemini-South 8 m (Zorro) - , LCO:1 m (Sinistro) - , SOAR: 4.1 m (HRCam) - , and TESS -

Software References

AstroImageJ (Collins et al. 2017) and TAPIR (Jensen 2013)

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