Mass determination of the 1:3:5 near-resonant planets transiting GJ 9827 (K2-135)
Journal article, 2018

Context. Multiplanet systems are excellent laboratories to test planet formation models as all planets are formed under the same initial conditions. In this context, systems transiting bright stars can play a key role, since planetary masses, radii, and bulk densities can be measured. Aims. GJ 9827 (K2-135) has recently been found to host a tightly packed system consisting of three transiting small planets whose orbital periods of 1.2, 3.6, and 6.2 days are near the 1:3:5 ratio. GJ 9827 hosts the nearest planetary system (~30 pc) detected by NASA's Kepler or K2 space mission. Its brightness (V = 10.35 mag) makes the star an ideal target for detailed studies of the properties of its planets. Methods. Combining the K2 photometry with high-precision radial-velocity measurements gathered with the FIES, HARPS, and HARPS-N spectrographs we revised the system parameters and derive the masses of the three planets. Results. We find that GJ 9827 b has a mass of Mb = 3.69-0.46+0.48 M and a radius of Rb = 1.58-0.13+0.14 R, yielding a mean density of ρb = 5.11-1.27+1.74 g cm-3. GJ 9827 c has a mass of Mc = 1.45-0.57+0.58 M, radius of Rc = 1.24-0.11+0.11 R, and a mean density of ρc = 4.13-1.77+2.31 g cm-3. For GJ 9827 d, we derive Md = 1.45-0.57+0.58 M, Rd = 1.24-0.11+0.11 R, and ρd = 1.51-0.53+0.71 g cm-3. Conclusions. GJ 9827 is one of the few known transiting planetary systems for which the masses of all planets have been determined with a precision better than 30%. This system is particularly interesting because all three planets are close to the limit between super-Earths and sub-Neptunes. The planetary bulk compositions are compatible with a scenario where all three planets formed with similar core and atmosphere compositions, and we speculate that while GJ 9827 b and GJ 9827 c lost their atmospheric envelopes, GJ 9827 d maintained its primordial atmosphere, owing to the much lower stellarirradiation. This makes GJ 9827 one of the very few systems where the dynamical evolution and the atmosphericescape can be studied in detail for all planets, helping us to understand how compact systems form and evolve.

Stars: individual: GJ 9827

Techniques: high angular resolution

Stars: abundances

Techniques: radial velocities

Planetary systems

Techniques: photometric

Author

J. Prieto-Arranz

Instituto Astrofisico de Canarias

University of La Laguna

E. Palle

Instituto Astrofisico de Canarias

University of La Laguna

D. Gandolfi

University of Turin

O. Barragán

University of Turin

E. W. Guenther

Instituto Astrofisico de Canarias

Thüringer Landessternwarte Tautenburg

Fei Dai

Massachusetts Institute of Technology (MIT)

Princeton University

Malcolm Fridlund

Leiden University

Chalmers, Space, Earth and Environment, Onsala Space Observatory

T. Hirano

Tokyo Institute of Technology

J. Livingston

University of Tokyo

R. Luque

Instituto Astrofisico de Canarias

University of La Laguna

Prajwal Niraula

Wesleyan University

Carina Persson

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

S. Redfield

Wesleyan University

Simon Albrecht

Aarhus University

R. Alonso

Instituto Astrofisico de Canarias

University of La Laguna

Giuliano Antoniciello

University of Turin

J. Cabrera

German Aerospace Center (DLR)

William D. Cochran

The University of Texas at Austin

Szilard Csizmadia

German Aerospace Center (DLR)

H. Deeg

Instituto Astrofisico de Canarias

University of La Laguna

P. Eigmüller

German Aerospace Center (DLR)

M. Endl

The University of Texas at Austin

Anders Erikson

German Aerospace Center (DLR)

M.E. Everett

National Optical Astronomy Observatory

A. Fukui

National Institutes of Natural Sciences - National Astronomical Observatory of Japan

S. Grziwa

University of Cologne

A. Hatzes

Thüringer Landessternwarte Tautenburg

D. Hidalgo

Instituto Astrofisico de Canarias

University of La Laguna

M. Hjorth

Aarhus University

Judith Korth

University of Cologne

D. Lorenzo-Oliveira

Universidade Cidade de Sao Paulo

F. Murgas

Aarhus University

Norio Narita

University of Tokyo

National Institutes of Natural Sciences

David Nespral

Instituto Astrofisico de Canarias

University of La Laguna

G. Nowak

University of La Laguna

Instituto Astrofisico de Canarias

Martin Pätzold

University of Cologne

P. Montañez Rodríguez

University of La Laguna

Instituto Astrofisico de Canarias

H. Rauer

German Aerospace Center (DLR)

Technische Universität Berlin

I. Ribas

Institute of Space Sciences (ICE) - CSIC

Institute of Space Studies of Catalonia (IEEC)

Alexis M. S. Smith

German Aerospace Center (DLR)

T. Trifonov

Max Planck Institute

Vincent Van Eylen

Leiden University

J. N. Winn

Princeton University

Astronomy and Astrophysics

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

Vol. 618 32872

Exoplanets from space – CHEOPS and PLATO, ESA’s next two projects

Swedish National Space Board, 2017-01-01 -- 2022-12-31.

Subject Categories

Astronomy, Astrophysics and Cosmology

Roots

Basic sciences

DOI

10.1051/0004-6361/201832872

More information

Latest update

1/18/2019