Masses and compositions of three small planets orbiting the nearby M dwarf L231-32 (TOI-270) and the M dwarf radius valley
Journal article, 2021
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.
planets and satellites: formation
planets and satellites: fundamental parameters
planets and satellites: composition
planets and satellites: individual: L231-32
Author
Vincent Van Eylen
University College London (UCL)
Princeton University
N. Astudillo-Defru
Universidad Catolica de la Santisima Concepcion
X. Bonfils
Grenoble Alpes University
J.H. Livingston
University of Tokyo
T. Hirano
Tokyo Institute of Technology
R. Luque
University of La Laguna
Instituto de Astrofísica de Canarias
K. W.F. Lam
Technische Universität Berlin
A.B. Justesen
Aarhus University
J. N. Winn
Princeton University
D. Gandolfi
University of Turin
G. Nowak
University of La Laguna
Instituto de Astrofísica de Canarias
Enric Palle
Instituto de Astrofísica de Canarias
University of La Laguna
Simon Albrecht
Aarhus University
Fei Dai
California Institute of Technology (Caltech)
B. Campos Estrada
Imperial College London
James E. Owen
Imperial College London
D. Foreman-Mackey
Flatiron Institute
Malcolm Fridlund
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Leiden University
Judith Korth
University of Cologne
S. Mathur
University of La Laguna
Instituto de Astrofísica de Canarias
T. Forveille
Grenoble Alpes University
T. Mikal-Evans
Massachusetts Institute of Technology (MIT)
H. L.M. Osborne
University College London (UCL)
C. S.K. Ho
University College London (UCL)
J. M. Almenara
Grenoble Alpes University
E. Artigau
Université de Montréal
O. Barragán
University of Oxford
S.C.C. Barros
University of Porto
F. Bouchy
University of Geneva
J. Cabrera
German Aerospace Center (DLR)
D. A. Caldwell
SETI Institute
D. Charbonneau
Harvard-Smithsonian Center for Astrophysics
Priyanka Chaturvedi
Thüringer Landessternwarte Tautenburg
William D. Cochran
The University of Texas at Austin
Szilard Csizmadia
German Aerospace Center (DLR)
Mario Damasso
Istituto nazionale di astrofisica (INAF)
X. Delfosse
Grenoble Alpes University
J. R. De Medeiros
Federal University of Rio Grande do Norte
R. F. Diaz
Consejo Nacional de Investigaciones Cientificas y Tecnicas
René Doyon
Université de Montréal
M. Esposito
Thüringer Landessternwarte Tautenburg
G. Furész
Massachusetts Institute of Technology (MIT)
P. Figueira
European Southern Observatory Santiago
University of Porto
Iskra Georgieva
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
E. Goffo
University of Turin
S. Grziwa
Massachusetts Institute of Technology (MIT)
E. W. Guenther
Thüringer Landessternwarte Tautenburg
A. Hatzes
Thüringer Landessternwarte Tautenburg
Jon M. Jenkins
NASA Ames Research Center
Petr Kabath
Czech Academy of Sciences
E. Knudstrup
Aarhus University
D. W. Latham
Harvard-Smithsonian Center for Astrophysics
B. Lavie
University of Geneva
C. Lovis
University of Geneva
R. E. Mennickent
University of Concepcion
S. E. Mullally
Space Telescope Science Institute (STScI)
F. Murgas
University of La Laguna
Instituto de Astrofísica de Canarias
Norio Narita
Astrobiology Center, Japan
University of Tokyo
University of La Laguna
Japan Science and Technology Agency
Francesco Pepe
University of Geneva
Carina Persson
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
S. Redfield
Wesleyan University
George R. Ricker
Massachusetts Institute of Technology (MIT)
N. C. Santos
University of Porto
S. Seager
Massachusetts Institute of Technology (MIT)
L. M. Serrano
University of Turin
Alexis M. S. Smith
German Aerospace Center (DLR)
A. Suárez Mascareño
Instituto de Astrofísica de Canarias
J. Šubjak
NASA Ames Research Center
J. D. Twicken
NASA Ames Research Center
SETI Institute
S. Udry
University of Geneva
Roland K. Vanderspek
Massachusetts Institute of Technology (MIT)
M. Zapatero-Osorio
Centro de Astrobiologia (CAB)
Monthly Notices of the Royal Astronomical Society
0035-8711 (ISSN) 1365-2966 (eISSN)
Vol. 507 2 2154-2173Subject Categories
Meteorology and Atmospheric Sciences
Astronomy, Astrophysics and Cosmology
Geophysics
DOI
10.1093/mnras/stab2143