Masses and compositions of three small planets orbiting the nearby M dwarf L231-32 (TOI-270) and the M dwarf radius valley
Artikel i vetenskaplig tidskrift, 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
Författare
Vincent Van Eylen
University College London (UCL)
Princeton University
N. Astudillo-Defru
Universidad Catolica de la Santisima Concepcion
X. Bonfils
Université Grenoble Alpes
J.H. Livingston
University of Tokyo
T. Hirano
Tokyo Institute of Technology
R. Luque
Universidad de la Laguna
Instituto de Astrofísica de Canarias
K. W.F. Lam
Technische Universität Berlin
A.B. Justesen
Aarhus Universitet
J. N. Winn
Princeton University
D. Gandolfi
Universita degli Studi di Torino
G. Nowak
Universidad de la Laguna
Instituto de Astrofísica de Canarias
Enric Palle
Instituto de Astrofísica de Canarias
Universidad de la Laguna
Simon Albrecht
Aarhus Universitet
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, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik
Universiteit Leiden
Judith Korth
Universität zu Köln
S. Mathur
Universidad de la Laguna
Instituto de Astrofísica de Canarias
T. Forveille
Université Grenoble Alpes
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
Université Grenoble Alpes
E. Artigau
Université de Montréal
O. Barragán
University of Oxford
S.C.C. Barros
Universidade do Porto
F. Bouchy
Université de Genève
J. Cabrera
Deutsches Zentrums für Luft- und Raumfahrt (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
Deutsches Zentrums für Luft- und Raumfahrt (DLR)
Mario Damasso
Istituto nazionale di astrofisica (INAF)
X. Delfosse
Université Grenoble Alpes
J. R. De Medeiros
Universidade Federal do 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
Universidade do Porto
Iskra Georgieva
Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik
E. Goffo
Universita degli Studi di Torino
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 Universitet
D. W. Latham
Harvard-Smithsonian Center for Astrophysics
B. Lavie
Université de Genève
C. Lovis
Université de Genève
R. E. Mennickent
Universidad de Concepción
S. E. Mullally
Space Telescope Science Institute (STScI)
F. Murgas
Universidad de la Laguna
Instituto de Astrofísica de Canarias
Norio Narita
Astrobiology Center, Japan
University of Tokyo
Universidad de la Laguna
Japan Science and Technology Agency
Francesco Pepe
Université de Genève
Carina Persson
Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik
S. Redfield
Wesleyan University
George R. Ricker
Massachusetts Institute of Technology (MIT)
N. C. Santos
Universidade do Porto
S. Seager
Massachusetts Institute of Technology (MIT)
L. M. Serrano
Universita degli Studi di Torino
Alexis M. S. Smith
Deutsches Zentrums für Luft- und Raumfahrt (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
Université de Genève
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 2154-2173Ämneskategorier
Meteorologi och atmosfärforskning
Astronomi, astrofysik och kosmologi
Geofysik
DOI
10.1093/mnras/stab2143