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: abundances
Stars: individual: GJ 9827
Techniques: radial velocities
Planetary systems
Techniques: high angular resolution
Techniques: photometric
Author
J. Prieto-Arranz
Instituto de Astrofísica de Canarias
University of La Laguna
E. Palle
University of La Laguna
Instituto de Astrofísica de Canarias
D. Gandolfi
University of Turin
O. Barragán
University of Turin
E. W. Guenther
Instituto de Astrofísica de Canarias
Thüringer Landessternwarte Tautenburg
Fei Dai
Massachusetts Institute of Technology (MIT)
Princeton University
Malcolm Fridlund
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Leiden University
T. Hirano
Tokyo Institute of Technology
J. Livingston
University of Tokyo
R. Luque
Instituto de Astrofísica de Canarias
University of La Laguna
Prajwal Niraula
Wesleyan University
Carina Persson
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
S. Redfield
Wesleyan University
Simon Albrecht
Aarhus University
R. Alonso
Instituto de Astrofísica 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
University of La Laguna
Instituto de Astrofísica de Canarias
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 Astronomical Observatory of Japan
S. Grziwa
University of Cologne
A. Hatzes
Thüringer Landessternwarte Tautenburg
D. Hidalgo
Instituto de Astrofísica 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
University of La Laguna
Instituto de Astrofísica de Canarias
G. Nowak
Instituto de Astrofísica de Canarias
University of La Laguna
Martin Pätzold
University of Cologne
P. Montañez Rodríguez
Instituto de Astrofísica de Canarias
University of La Laguna
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 Society
Vincent Van Eylen
Leiden University
J. N. Winn
Princeton University
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 618 32872Exoplanets from space – CHEOPS and PLATO, ESA’s next two projects
Swedish National Space Board (174/18), 2017-01-01 -- 2022-12-31.
Subject Categories
Astronomy, Astrophysics and Cosmology
Roots
Basic sciences
DOI
10.1051/0004-6361/201832872