Precise mass determination for the keystone sub-Neptune planet transiting the mid-type M dwarf G 9-40
Journal article, 2022
Context. Despite being a prominent subset of the exoplanet population discovered in the past three decades, the nature and provenance of sub-Neptune-sized planets is still one of the open questions in exoplanet science. Aims. For planets orbiting bright stars, precisely measuring the orbital and planet parameters of the system is the best approach to distinguish between competing theories regarding their formation and evolution. Methods. We obtained 69 new radial velocity observations of the mid-M dwarf G 9-40 with the CARMENES instrument to measure for the first time the mass of its transiting sub-Neptune planet, G 9-40 b, discovered in data from the K2 mission. Results. Combined with new observations from the TESS mission during Sectors 44, 45, and 46, we are able to measure the radius of the planet to an uncertainty of 3.4% (R-b = 1.900 +/- 0.065 R-circle plus) and determine its mass with a precision of 16% (M-b = 4.00 +/- 0.63 M-circle plus). The resulting bulk density of the planet is inconsistent with a terrestrial composition and suggests the presence of either a water-rich core or a significant hydrogen-rich envelope. Conclusions. G 9-40 b is referred to as a keystone planet due to its location in period-radius space within the radius valley. Several theories offer explanations for the origin and properties of this population and this planet is a valuable target for testing the dependence of those models on stellar host mass. By virtue of its brightness and small size of the host, it joins L 98-59 d as one of the two best warm (T-eq similar to 400 K) sub-Neptunes for atmospheric characterization with JWST, which will probe cloud formation in sub-Neptune-sized planets and break the degeneracies of internal composition models.
stars: low-mass
techniques: radial velocities
planetary systems
stars: individual: G 9-40
techniques: photometric
Author
R. Luque
University of Chicago
Spanish National Research Council (CSIC)
G. Nowak
Instituto de Astrofísica de Canarias
University of La Laguna
T. Hirano
Astrobiology Center, Japan
D. Kossakowski
Max Planck Society
E. Palle
Instituto de Astrofísica de Canarias
University of La Laguna
M. C. Nixon
University of Cambridge
G. Morello
Instituto de Astrofísica de Canarias
University of La Laguna
P. J. Amado
Spanish National Research Council (CSIC)
S. H. Albrecht
Aarhus University
J. A. Caballero
European Space Astronomy Centre (ESAC)
C. Cifuentes
European Space Astronomy Centre (ESAC)
W. D. Cochran
The University of Texas at Austin
H. J. Deeg
Instituto de Astrofísica de Canarias
University of La Laguna
S. Dreizler
University of Göttingen
E. Esparza-Borges
University of La Laguna
Instituto de Astrofísica de Canarias
A. Fukui
Instituto de Astrofísica de Canarias
University of Tokyo
D. Gandolfi
University of Turin
E. Goffo
Thüringer Landessternwarte Tautenburg
University of Turin
E. W. Guenther
Thüringer Landessternwarte Tautenburg
A. P. Hatzes
Thüringer Landessternwarte Tautenburg
T. Henning
Max Planck Society
P. Kabath
Czech Academy of Sciences
K. Kawauchi
Instituto de Astrofísica de Canarias
University of La Laguna
Judith Korth
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
T. Kotani
National Astronomical Observatory of Japan
T. Kudo
National Astronomical Observatory of Japan
M. Kuzuhara
National Astronomical Observatory of Japan
M. Lafarga
The University of Warwick
K. W. F. Lam
German Aerospace Center (DLR)
J. Livingston
Astrobiology Center, Japan
The Graduate University for Advanced Studies (SOKENDAI)
National Astronomical Observatory of Japan
J. C. Morales
Centre Tecnològic de Telecomunicacions de Catalunya (CTTC)
Spanish National Research Council (CSIC)
Alexandra Muresan
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
F. Murgas
Instituto de Astrofísica de Canarias
University of La Laguna
N. Narita
Astrobiology Center, Japan
University of Tokyo
Instituto de Astrofísica de Canarias
H. L. M. Osborne
University College London (UCL)
H. Parviainen
Instituto de Astrofísica de Canarias
University of La Laguna
V. M. Passegger
Hamburg Observatory
University of Oklahoma
Carina Persson
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
A. Quirrenbach
Heidelberg University
S. Redfield
Wesleyan University
S. Reffert
Heidelberg University
A. Reiners
University of Göttingen
I Ribas
Centre Tecnològic de Telecomunicacions de Catalunya (CTTC)
Spanish National Research Council (CSIC)
L. M. Serrano
University of Turin
M. Tamura
National Astronomical Observatory of Japan
University of Tokyo
Astrobiology Center, Japan
V. Van Eylen
University College London (UCL)
N. Watanabe
University of Tokyo
M. R. Zapatero Osorio
Spanish National Research Council (CSIC)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 666 A154Subject Categories (SSIF 2011)
Meteorology and Atmospheric Sciences
Astronomy, Astrophysics and Cosmology
Other Physics Topics
DOI
10.1051/0004-6361/202244426