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.

planets and satellites: detection

techniques: photometric

techniques: spectroscopic

methods: observational

techniques: radial velocities

techniques: high angular resolution


Teruyuki Hirano

Tokyo Institute of Technology

Fei Dai

Department of Astrophysical Sciences, Princeton University

Massachusetts Institute of Technology (MIT)

D. Gandolfi

University of Turin

Akihiko Fukui

John H. Livingston

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

Leiden University

Complutense University

M. Kuzuhara

National Institutes of Natural Sciences

National Astronomical Observatory of Japan

David Montes

Complutense University

Tsuguru Ryu

National Astronomical Observatory of Japan

The Graduate University for Advanced Studies (SOKENDAI)

Simon Albrecht

Aarhus University

Oscar Barragan

Juan Cabrera

Szilard Csizmadia

Hans Deeg

Philipp Eigmüller

Anders Erikson

Malcolm Fridlund

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

Sascha Grziwa

Eike W. Guenther

Artie P. Hatzes

Judith Korth

T. Kudo

Nobuhiko Kusakabe

Norio Narita

David Nespral

Grzegorz Nowak

Martin Pätzold

Enric Palle

Carina Persson

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

Jorge Prieto-Arranz

Heike Rauer

I. Ribas

B. Sato

Alexis M. S. Smith

M. Tamura

Yusuke Tanaka

Vincent Van Eylen

Joshua N. Winn

Astronomical Journal

0004-6256 (ISSN) 1538-3881 (eISSN)

Vol. 155 3 127-

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


Basic sciences



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