Exoplanets around Low-mass Stars Unveiled by K2
Journal article, 2018
We present the detection and follow-up observations of planetary candidates around low-mass stars observed by the K2 mission. Based on light-curve analysis, adaptive-optics imaging, and optical spectroscopy at low and high resolution (including radial velocity measurements), we validate 16 planets around 12 low-mass stars observed during K2 campaigns 5–10. Among the 16 planets, 12 are newly validated, with orbital periods ranging from 0.96 to 33 days. For one of the planets (K2-151b), we present ground-based transit photometry, allowing us to refine the ephemerides. Combining our K2 M-dwarf planets together with the validated or confirmed planets found previously, we investigate the dependence of planet radius R p on stellar insolation and metallicity [Fe/H]. We confirm that for periods P ≲ 2 days, planets with a radius Rp≳ 2 R⊕ are less common than planets with a radius between 1–2 R⊕. We also see a hint of the “radius valley” between 1.5 and 2 R⊕, which has been seen for close-in planets around FGK stars. These features in the radius/period distribution could be attributed to photoevaporation of planetary envelopes by high-energy photons from the host star, as they have for FGK stars. For the M dwarfs, though, the features are not as well defined, and we cannot rule out other explanations such as atmospheric loss from internal planetary heat sources or truncation of the protoplanetary disk. There also appears to be a relation between planet size and metallicity: the few planets larger than about 3 R⊕ are found around the most metal-rich M dwarfs.
techniques: spectroscopic
techniques: radial velocities
planets and satellites: detection
methods: observational
techniques: photometric
techniques: high angular resolution
Author
Teruyuki Hirano
Tokyo Institute of Technology
Fei Dai
Princeton University
Massachusetts Institute of Technology (MIT)
D. Gandolfi
University of Turin
Akihiko Fukui
National Astronomical Observatory of Japan
John H. Livingston
University of Tokyo
Kohei Miyakawa
Tokyo Institute of Technology
Michael Endl
The University of Texas at Austin
William D. Cochran
The University of Texas at Austin
Francisco J. Alonso-Floriano
Complutense University
Leiden University
M. Kuzuhara
National Astronomical Observatory of Japan
National Institutes of Natural Sciences
David Montes
Complutense University
Tsuguru Ryu
The Graduate University for Advanced Studies (SOKENDAI)
National Astronomical Observatory of Japan
Simon Albrecht
Aarhus University
Oscar Barragan
University of Turin
Juan Cabrera
German Aerospace Center (DLR)
Szilard Csizmadia
German Aerospace Center (DLR)
Hans Deeg
German Aerospace Center (DLR)
Instituto de Astrofísica de Canarias
Philipp Eigmüller
German Aerospace Center (DLR)
Anders Erikson
German Aerospace Center (DLR)
Malcolm Fridlund
Leiden University
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Sascha Grziwa
University of Cologne
Eike W. Guenther
Thüringer Landessternwarte Tautenburg
Artie P. Hatzes
Thüringer Landessternwarte Tautenburg
Judith Korth
University of Cologne
T. Kudo
National Astronomical Observatory of Japan
Nobuhiko Kusakabe
National Astronomical Observatory of Japan
National Institutes of Natural Sciences
Norio Narita
National Institutes of Natural Sciences
University of Tokyo
David Nespral
University of La Laguna
Instituto de Astrofísica de Canarias
Grzegorz Nowak
University of La Laguna
Instituto de Astrofísica de Canarias
Martin Pätzold
University of Cologne
Enric Palle
Instituto de Astrofísica de Canarias
University of La Laguna
Carina Persson
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Jorge Prieto-Arranz
Instituto de Astrofísica de Canarias
University of La Laguna
Heike Rauer
Technische Universität Berlin
German Aerospace Center (DLR)
I. Ribas
Institute of Space Studies of Catalonia (IEEC)
B. Sato
Tokyo Institute of Technology
Alexis M. S. Smith
German Aerospace Center (DLR)
M. Tamura
National Institutes of Natural Sciences
University of Tokyo
National Astronomical Observatory of Japan
Yusuke Tanaka
University of Tokyo
Vincent Van Eylen
Leiden University
Joshua N. Winn
Princeton University
Astronomical Journal
0004-6256 (ISSN) 1538-3881 (eISSN)
Vol. 155 3 127- 127Exoplanets 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
10.3847/1538-3881/aaa9c1