Bibcode
Hirano, T.; Dai, Fei; Gandolfi, Davide; Fukui, Akihiko; Livingston, John H.; Miyakawa, Kohei; Endl, Michael; Cochran, William D.; Alonso-Floriano, Francisco J.; Kuzuhara, Masayuki; Montes, David; Ryu, Tsuguru; Albrecht, Simon; Barragan, Oscar; Cabrera, Juan; Csizmadia, Szilard; Deeg, Hans; Eigmüller, Philipp; Erikson, Anders; Fridlund, Malcolm; Grziwa, Sascha; Guenther, Eike W.; Hatzes, Artie P.; Korth, Judith; Kudo, Tomoyuki; Kusakabe, Nobuhiko; Narita, Norio; Nespral, D.; Nowak, G.; Pätzold, Martin; Palle, E.; ina M.; Prieto-Arranz, J.; Rauer, Heike; Ribas, Ignasi; Sato, Bun’ei; Smith, Alexis M. S.; Tamura, Motohide; Tanaka, Yusuke; Van Eylen, Vincent; Winn, Joshua N.
Bibliographical reference
The Astronomical Journal, Volume 155, Issue 3, article id. 127, 23 pp. (2018).
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3
2018
Citations
77
Refereed citations
74
Description
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 {R}p≳ 2 {R}\oplus 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.
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