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: fundamental parameters

Planets and satellites: dynamical evolution and stability

Planets and satellites: detection

Planets and satellites: atmospheres

Planetary systems

Author

Enric Palle

University of La Laguna

Instituto Astrofisico de Canarias

G. Nowak

Instituto Astrofisico de Canarias

University of La Laguna

R. Luque

Instituto Astrofisico de Canarias

University of La Laguna

D. Hidalgo

University of La Laguna

Instituto Astrofisico de Canarias

O. Barragán

University of Turin

J. Prieto-Arranz

Instituto Astrofisico de Canarias

University of La Laguna

T. Hirano

Tokyo Institute of Technology

C.W.M. 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

Instituto Astrofisico de Canarias

University of La Laguna

P. J. Amado

CSIC - Instituto de Astrofísica de Andalucía (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

Instituto Astrofisico de Canarias

University of La Laguna

P. Eigmüller

German Aerospace Center (DLR)

Technische Universität Berlin

M. Endl

The University of Texas at Austin

Anders Erikson

German Aerospace Center (DLR)

A. Fukui

National Astronomical Observatory of Japan

Instituto Astrofisico de Canarias

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 Institute

M. Kuzuhara

National Institutes of Natural Sciences

National Astronomical Observatory of Japan

P. M. Rodriguez

University of La Laguna

Instituto Astrofisico de Canarias

F. Murgas

University of La Laguna

Instituto Astrofisico de Canarias

Norio Narita

National Astronomical Observatory of Japan

Instituto Astrofisico de Canarias

David Nespral

Instituto Astrofisico de Canarias

University of La Laguna

Martin Pätzold

University of Cologne

Carina Persson

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

A. Quirrenbach

Heidelberg-Königstuhl State Observatory

H. Rauer

German Aerospace Center (DLR)

Freie Universität Berlin

Technische Universität Berlin

S. Redfield

Wesleyan University

A. Reiners

University of Göttingen

I. Ribas

Universitat Autonoma de Barcelona (UAB)

Institute of Space Studies of Catalonia (IEEC)

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 A41

Subject Categories

Astronomy, Astrophysics and Cosmology

Roots

Basic sciences

DOI

10.1051/0004-6361/201834001

More information

Latest update

9/10/2019