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Anders Zinck Justesen

Masses and compositions of three small planets orbiting the nearby M dwarf L231-32 (TOI-270) and the M dwarf radius valley

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  • V. Van Eylen, University College London, Princeton University
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  • N. Astudillo-Defru, Universidad Católica de la Santísima Concepción
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  • X. Bonfils, Universite Grenoble Alpes
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  • J. Livingston, University of Tokyo
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  • T. Hirano, Tokyo Institute of Technology
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  • R. Luque, University of La Laguna, Instituto Astrofisico de Canarias
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  • K. W.F. Lam, Technical University of Berlin
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  • A. B. Justesen
  • J. N. Winn, Princeton University
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  • D. Gandolfi, University of Turin
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  • G. Nowak, University of La Laguna, Instituto Astrofisico de Canarias
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  • E. Palle, University of La Laguna, Instituto Astrofisico de Canarias
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  • S. Albrecht
  • F. Dai, California Institute of Technology
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  • B. Campos Estrada, Imperial College London
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  • J. E. Owen, Imperial College London
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  • D. Foreman-Mackey, Simons Foundation
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  • M. Fridlund, Chalmers University of Technology, Leiden University
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  • J. Korth, University of Cologne
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  • S. Mathur, University of La Laguna, Instituto Astrofisico de Canarias
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  • T. Forveille, Universite Grenoble Alpes
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  • T. Mikal-Evans, Massachusetts Institute of Technology
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  • H. L.M. Osborne, University College London
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  • C. S.K. Ho, University College London
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  • J. M. Almenara, Universite Grenoble Alpes
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  • E. Artigau, Institut de Recherche sur les Exoplanètes
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  • O. Barragán, University of Oxford
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  • S. C.C. Barros, University of Porto
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  • F. Bouchy, Université de Genève
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  • J. Cabrera, German Aerospace Center
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  • D. A. Caldwell, SETI Institute
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  • D. Charbonneau, Harvard University
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  • P. Chaturvedi, Karl Schwarzschild Observatory
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  • W. D. Cochran, University of Texas at Austin
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  • S. Csizmadia, German Aerospace Center
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  • M. Damasso, National Institute for Astrophysics
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  • X. Delfosse, Universite Grenoble Alpes
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  • J. R. De Medeiros, Universidade Federal do Rio Grande do Norte
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  • R. F. Díaz, Consejo Nacional de Investigaciones Científicas y Técnicas
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  • R. Doyon, Institut de Recherche sur les Exoplanètes
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  • M. Esposito, Karl Schwarzschild Observatory
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  • G. Furész, Massachusetts Institute of Technology
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  • P. Figueira, University of Porto, European Southern Observatory
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  • I. Georgieva, Chalmers University of Technology
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  • E. Goffo, University of Turin
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  • S. Grziwa, Massachusetts Institute of Technology
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  • E. Guenther, Karl Schwarzschild Observatory
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  • A. P. Hatzes, Karl Schwarzschild Observatory
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  • J. M. Jenkins, NASA Ames Research Center
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  • P. Kabath, Czech Academy of Sciences
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  • E. Knudstrup
  • D. W. Latham, Harvard University
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  • B. Lavie, Université de Genève
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  • C. Lovis, Université de Genève
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  • R. E. Mennickent, Universidad de Concepcion
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  • S. E. Mullally, Space Telescope Science Institute
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  • F. Murgas, University of La Laguna, Instituto Astrofisico de Canarias
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  • N. Narita, University of La Laguna, University of Tokyo, Japan Science and Technology Agency, National Institutes of Natural Sciences - AstroBiology Center
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  • F. A. Pepe, Université de Genève
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  • C. M. Persson, Chalmers University of Technology
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  • S. Redfield, Wesleyan University
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  • G. R. Ricker, Massachusetts Institute of Technology
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  • N. C. Santos, University of Porto
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  • S. Seager, Massachusetts Institute of Technology
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  • L. M. Serrano, University of Turin
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  • A. M.S. Smith, German Aerospace Center
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  • A. Suárez Mascareño, Instituto Astrofisico de Canarias
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  • J. Subjak, NASA Ames Research Center
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  • J. D. Twicken, SETI Institute, NASA Ames Research Center
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  • S. Udry, Université de Genève
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  • R. Vanderspek, Massachusetts Institute of Technology
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  • M. R. Zapatero Osorio, ?Astrobiology Center

We report on precise Doppler measurements of L231-32 (TOI-270), a nearby M dwarf (d = 22 pc, M = 0.39 M, R = 0.38 R), which hosts three transiting planets that were recently discovered using data from the Transiting Exoplanet Survey Satellite (TESS). The three planets are 1.2, 2.4, and 2.1 times the size of Earth and have orbital periods of 3.4, 5.7, and 11.4 d. We obtained 29 high-resolution optical spectra with the newly commissioned Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) and 58 spectra using the High Accuracy Radial velocity Planet Searcher (HARPS). From these observations, we find the masses of the planets to be 1.58 ± 0.26, 6.15 ± 0.37, and 4.78 ± 0.43 M, respectively. The combination of radius and mass measurements suggests that the innermost planet has a rocky composition similar to that of Earth, while the outer two planets have lower densities. Thus, the inner planet and the outer planets are on opposite sides of the 'radius valley'-a region in the radius-period diagram with relatively few members-which has been interpreted as a consequence of atmospheric photoevaporation. We place these findings into the context of other small close-in planets orbiting M dwarf stars, and use support vector machines to determine the location and slope of the M dwarf (Teff < 4000 K) radius valley as a function of orbital period. We compare the location of the M dwarf radius valley to the radius valley observed for FGK stars, and find that its location is a good match to photoevaporation and core-powered mass-loss models. Finally, we show that planets below the M dwarf radius valley have compositions consistent with stripped rocky cores, whereas most planets above have a lower density consistent with the presence of a H-He atmosphere.

OriginalsprogEngelsk
TidsskriftMonthly Notices of the Royal Astronomical Society
Vol/bind507
Nummer2
Sider (fra-til)2154-2173
Antal sider20
ISSN0035-8711
DOI
StatusUdgivet - okt. 2021

Bibliografisk note

Publisher Copyright:
© 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.

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