Detection and Doppler monitoring of K2-285 (EPIC 246471491), a system of four transiting planets smaller than Neptune
Journal article, 2019
Context. The Kepler extended mission, also known as K2, has provided the community with a wealth of planetary candidates that orbit stars typically much brighter than the targets of the original mission. These planet candidates are suitable for further spectroscopic follow-up and precise mass determinations, leading ultimately to the construction of empirical mass-radius diagrams. Particularly interesting is to constrain the properties of planets that are between Earth and Neptune in size, the most abundant type of planet orbiting Sun-like stars with periods of less than a few years. Aims. Among many other K2 candidates, we discovered a multi-planetary system around EPIC 246471491, referred to henceforth as K2-285, which contains four planets, ranging in size from twice the size of Earth to nearly the size of Neptune. We aim here at confirming their planetary nature and characterizing the properties of this system. Methods. We measure the mass of the planets of the K2-285 system by means of precise radial-velocity measurements using the CARMENES spectrograph and the HARPS-N spectrograph. Results. With our data we are able to determine the mass of the two inner planets of the system with a precision better than 15%, and place upper limits on the masses of the two outer planets. Conclusions. We find that K2-285b has a mass of M b = 9.68 -1.37+1.21 M · and a radius of R b = 2.59 -0.06+0.06 R · , yielding a mean density of ρ b = 3.07 -0.45+0.45 g cm -3 , while K2-285c has a mass of M c = 15.68 -2.13+2.28 M · , radius of R c = 3.53 -0.08+0.08 R · , and a mean density of ρ c = 1.95 -0.28+0.32 g cm -3 . For K2-285d (R d = 2.48 -0.06+0.06 R · ) and K2-285e (R e = 1.95 -0.05+0.05 R · ), the upper limits for the masses are 6.5 M · and 10.7 M · , respectively. The system is thus composed of an (almost) Neptune-twin planet (in mass and radius), two sub-Neptunes with very different densities and presumably bulk composition, and a fourth planet in the outermost orbit that resides right in the middle of the super-Earth/sub-Neptune radius gap. Future comparative planetology studies of this system would provide useful insights into planetary formation, and also a good test of atmospheric escape and evolution theories.
Planets and satellites: atmospheres
Planets and satellites: fundamental parameters
Planets and satellites: detection
Planets and satellites: dynamical evolution and stability
Planetary systems
Author
Enric Palle
University of La Laguna
Instituto de Astrofísica de Canarias
G. Nowak
Instituto de Astrofísica de Canarias
University of La Laguna
R. Luque
Instituto de Astrofísica de Canarias
University of La Laguna
D. Hidalgo
Instituto de Astrofísica de Canarias
University of La Laguna
O. Barragán
University of Turin
J. Prieto-Arranz
Instituto de Astrofísica de Canarias
University of La Laguna
T. Hirano
Tokyo Institute of Technology
Malcolm Fridlund
Leiden University
D. Gandolfi
University of Turin
J. Livingston
University of Tokyo
Fei Dai
Princeton University
Massachusetts Institute of Technology (MIT)
Juan Carlos Morales
Institute of Space Studies of Catalonia (IEEC)
Universitat Autonoma de Barcelona (UAB)
Marina Lafarga
Institute of Space Studies of Catalonia (IEEC)
Universitat Autonoma de Barcelona (UAB)
Simon Albrecht
Aarhus University
R. Alonso
University of La Laguna
Instituto de Astrofísica de Canarias
P. J. Amado
Institute of Astrophysics of Andalusia (IAA)
J. A. Caballero
Centro de Astrobiologia (CAB)
J. Cabrera
German Aerospace Center (DLR)
William D. Cochran
Freie Universität Berlin
Szilard Csizmadia
German Aerospace Center (DLR)
H. Deeg
University of La Laguna
Instituto de Astrofísica de Canarias
P. Eigmüller
Technische Universität Berlin
German Aerospace Center (DLR)
M. Endl
The University of Texas at Austin
Anders Erikson
German Aerospace Center (DLR)
A. Fukui
Instituto de Astrofísica de Canarias
National Astronomical Observatory of Japan
E. W. Guenther
Thüringer Landessternwarte Tautenburg
S. Grziwa
University of Cologne
A. Hatzes
Thüringer Landessternwarte Tautenburg
Judith Korth
University of Cologne
M. Kürster
Max Planck Society
M. Kuzuhara
National Institutes of Natural Sciences
National Astronomical Observatory of Japan
P. M. Rodriguez
University of La Laguna
Instituto de Astrofísica de Canarias
F. Murgas
University of La Laguna
Instituto de Astrofísica de Canarias
Norio Narita
Instituto de Astrofísica de Canarias
National Astronomical Observatory of Japan
David Nespral
Instituto de Astrofísica de Canarias
University of La Laguna
Martin Pätzold
University of Cologne
Carina Persson
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
A. Quirrenbach
Heidelberg-Königstuhl State Observatory
H. Rauer
Technische Universität Berlin
German Aerospace Center (DLR)
Freie Universität Berlin
S. Redfield
Wesleyan University
A. Reiners
University of Göttingen
I. Ribas
Institute of Space Studies of Catalonia (IEEC)
Universitat Autonoma de Barcelona (UAB)
Alexis M. S. Smith
German Aerospace Center (DLR)
Vincent Van Eylen
Leiden University
J. N. Winn
Princeton University
M. Zechmeister
University of Göttingen
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 623 A41Subject Categories
Astronomy, Astrophysics and Cosmology
Roots
Basic sciences
DOI
10.1051/0004-6361/201834001