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, Extragalaktisk astrofysik

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 2154-2173

Ämneskategorier

Meteorologi och atmosfärforskning

Astronomi, astrofysik och kosmologi

Geofysik

DOI

10.1093/mnras/stab2143

Mer information

Senast uppdaterat

2021-10-18