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- 127

Exoplanets 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

More information

Latest update

4/5/2022 6