A planetary system with two transiting mini-Neptunes near the radius valley transition around the bright M dwarf TOI-776
Journal article, 2021

We report the discovery and characterization of two transiting planets around the bright M1 V star LP 961-53 (TOI-776, J = 8.5 mag, M = 0.54 ± 0.03 M⊙) detected during Sector 10 observations of the Transiting Exoplanet Survey Satellite (TESS). Combining the TESS photometry with HARPS radial velocities, as well as ground-based follow-up transit observations from the MEarth and LCOGT telescopes, for the inner planet, TOI-776 b, we measured a period of Pb = 8.25 d, a radius of Rb = 1.85 ± 0.13 R⊙, and a mass of Mb = 4.0 ± 0.9 M⊙; and for the outer planet, TOI-776 c, a period of Pc = 15.66 d, a radius of Rc = 2.02 ± 0.14 R⊙, and a mass of Mc = 5.3 ± 1.8 M⊙. The Doppler data shows one additional signal, with a period of ~34 d, associated with the rotational period of the star. The analysis of fifteen years of ground-based photometric monitoring data and the inspection of different spectral line indicators confirm this assumption. The bulk densities of TOI-776 b and c allow for a wide range of possible interior and atmospheric compositions. However, both planets have retained a significant atmosphere, with slightly different envelope mass fractions. Thanks to their location near the radius gap for M dwarfs, we can start to explore the mechanism(s) responsible for the radius valley emergence around low-mass stars as compared to solar-like stars. While a larger sample of well-characterized planets in this parameter space is still needed to draw firm conclusions, we tentatively estimate that the stellar mass below which thermally-driven mass loss is no longer the main formation pathway for sculpting the radius valley is between 0.63 and 0.54 M⊙. Due to the brightness of the star, the TOI-776 system is also an excellent target for the James Webb Space Telescope, providing a remarkable laboratory in which to break the degeneracy in planetary interior models and to test formation and evolution theories of small planets around low-mass stars.

Techniques: radial velocities

Techniques: photometric

Stars: low-mass

Stars: individual: LP 961-53

Planetary systems

Author

R. Luque

Instituto de Astrofísica de Canarias

University of La Laguna

L. M. Serrano

University of Turin

K. Molaverdikhani

Heidelberg-Königstuhl State Observatory

Max Planck Society

M. C. Nixon

University of Cambridge

J. H. Livingston

University of Tokyo

E. W. Guenther

Thüringer Landessternwarte Tautenburg

E. Palle

Instituto de Astrofísica de Canarias

University of La Laguna

N. Madhusudhan

University of Cambridge

G. Nowak

Instituto de Astrofísica de Canarias

University of La Laguna

Judith Korth

University of Cologne

W. D. Cochran

The University of Texas at Austin

T. Hirano

Tokyo Institute of Technology

Priyanka Chaturvedi

Thüringer Landessternwarte Tautenburg

E. Goffo

University of Turin

S. Albrecht

Aarhus University

O. Barragán

University of Oxford

C. Briceño

Cerro Tololo Inter American Observatory

J. Cabrera

German Aerospace Center (DLR)

D. Charbonneau

Harvard-Smithsonian Center for Astrophysics

R. Cloutier

Harvard-Smithsonian Center for Astrophysics

K. A. Collins

Harvard-Smithsonian Center for Astrophysics

Kevin I. Collins

George Mason University

K. D. Colón

NASA Goddard Space Flight Center

I. J.M. Crossfield

University of Kansas

Szilard Csizmadia

German Aerospace Center (DLR)

Fei Dai

California Institute of Technology (Caltech)

H. J. Deeg

Instituto de Astrofísica de Canarias

University of La Laguna

M. Esposito

Thüringer Landessternwarte Tautenburg

Malcolm Fridlund

Leiden University

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

D. Gandolfi

University of Turin

Iskra Georgieva

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

Ana Glidden

Massachusetts Institute of Technology (MIT)

Robert Goeke

Massachusetts Institute of Technology (MIT)

S. Grziwa

University of Cologne

A. Hatzes

Thüringer Landessternwarte Tautenburg

C. E. Henze

NASA Ames Research Center

S. B. Howell

NASA Ames Research Center

J. Irwin

Harvard-Smithsonian Center for Astrophysics

J. M. Jenkins

NASA Ames Research Center

E. L.N. Jensen

Swarthmore College

Petr Kabath

Czech Academy of Sciences

R. C. Kidwell

Space Telescope Science Institute (STScI)

J. F. Kielkopf

University of Louisville

E. Knudstrup

Aarhus University

K. W.F. Lam

Technische Universität Berlin

D. W. Latham

Harvard-Smithsonian Center for Astrophysics

Jack J. Lissauer

NASA Ames Research Center

A. W. Mann

The University of North Carolina at Chapel Hill

Elisabeth Matthews

Massachusetts Institute of Technology (MIT)

Ismael Mireles

Massachusetts Institute of Technology (MIT)

N. Narita

Instituto de Astrofísica de Canarias

Japan Science and Technology Agency

University of Tokyo

National Institutes of Natural Sciences

M. Paegert

Harvard-Smithsonian Center for Astrophysics

Carina Persson

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

S. Redfield

Wesleyan University

George R. Ricker

Massachusetts Institute of Technology (MIT)

F. Rodler

European Southern Observatory Santiago

Joshua E. Schlieder

NASA Goddard Space Flight Center

N. J. Scott

NASA Ames Research Center

S. Seager

Massachusetts Institute of Technology (MIT)

J. Šubjak

Czech Academy of Sciences

T. G. Tan

Perth Exoplanet Survey Telescope

Eric B. Ting

NASA Ames Research Center

Roland K. Vanderspek

Massachusetts Institute of Technology (MIT)

Vincent Van Eylen

University College London (UCL)

J. N. Winn

Princeton University

C. Ziegler

University of Toronto

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 645 A41

Subject Categories

Meteorology and Atmospheric Sciences

Astronomy, Astrophysics and Cosmology

Geophysics

DOI

10.1051/0004-6361/202039455

More information

Latest update

11/12/2021