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.

planetary systems

stars: low-mass

stars: individual: G 9-40

techniques: radial velocities

techniques: photometric

Author

R. Luque

University of Chicago

Institute of Astrophysics of Andalusia (IAA)

G. Nowak

University of La Laguna

Instituto de Astrofísica de Canarias

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

University of La Laguna

Instituto de Astrofísica de Canarias

P. J. Amado

Institute of Astrophysics of Andalusia (IAA)

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

Instituto de Astrofísica de Canarias

University of La Laguna

A. Fukui

Instituto de Astrofísica de Canarias

University of Tokyo

D. Gandolfi

University of Turin

E. Goffo

University of Turin

Thüringer Landessternwarte Tautenburg

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

University of La Laguna

Instituto de Astrofísica de Canarias

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

Institute of Space Studies of Catalonia (IEEC)

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

Instituto de Astrofísica de Canarias

Astrobiology Center, Japan

University of Tokyo

H. L. M. Osborne

University College London (UCL)

H. Parviainen

Instituto de Astrofísica de Canarias

University of La Laguna

V. M. Passegger

University of Oklahoma

Hamburg Observatory

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

Spanish National Research Council (CSIC)

Institute of Space Studies of Catalonia (IEEC)

L. M. Serrano

University of Turin

M. Tamura

University of Tokyo

Astrobiology Center, Japan

National Astronomical Observatory of Japan

V. Van Eylen

University College London (UCL)

N. Watanabe

University of Tokyo

M. R. Zapatero Osorio

Spanish Astrobiology Center (INTA-CSIC)

Astronomy and Astrophysics

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

Vol. 666 A154

Subject Categories

Meteorology and Atmospheric Sciences

Astronomy, Astrophysics and Cosmology

Other Physics Topics

DOI

10.1051/0004-6361/202244426

More information

Latest update

11/16/2022