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.
Stars: individual: LP 961-53
Planetary systems
Stars: low-mass
Techniques: radial velocities
Techniques: photometric
Author
R. Luque
Instituto de Astrofísica de Canarias
University of La Laguna
L. M. Serrano
University of Turin
K. Molaverdikhani
Max Planck Society
Heidelberg-Königstuhl State Observatory
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
University of La Laguna
Instituto de Astrofísica de Canarias
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
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Leiden University
D. Gandolfi
University of Turin
Iskra Georgieva
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
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 System
Elisabeth Matthews
Massachusetts Institute of Technology (MIT)
Ismael Mireles
Massachusetts Institute of Technology (MIT)
N. Narita
University of Tokyo
National Institutes of Natural Sciences
Instituto de Astrofísica de Canarias
Japan Science and Technology Agency
M. Paegert
Harvard-Smithsonian Center for Astrophysics
Carina Persson
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
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 A41Subject Categories
Meteorology and Atmospheric Sciences
Astronomy, Astrophysics and Cosmology
Geophysics
DOI
10.1051/0004-6361/202039455