Super-Earth of 8 Mearth in a 2.2-day orbit around the K5V star K2-216
Artikel i vetenskaplig tidskrift, 2018

Although thousands of exoplanets have been discovered to date, far fewer have been fully characterised, in particular super- Earths. The KESPRINT consortium identified K2-216 as a planetary candidate host star in the K2 space mission Campaign 8 field with a transiting super-Earth. The planet has recently been validated as well. Our aim was to confirm the detection and derive the main physical characteristics of K2-216b, including the mass. We performed a series of follow-up observations: high resolution imaging with the FastCam camera at the TCS, the Infrared Camera and Spectrograph at Subaru, and high resolution spectroscopy with HARPS (ESO, La Silla), HARPS-N (TNG), and FIES (NOT). The stellar spectra were analyzed with the SpecMatch-Emp and SME codes to derive the stellar fundamental properties. We analyzed the K2 light curve with the Pyaneti software. The radial-velocity measurements were modelled with both a Gaussian process (GP) regression and the floating chunk offset (FCO) technique to simultaneously model the planetary signal and correlated noise associated with stellar activity. Imaging confirms that K2-216 is a single star. Our analysis discloses that the star is a moderately active K5V star of mass 0.70+/-0.03 Msun and radius 0.72+/-0.03 Rsun. Planet b is found to have a radius of 1.75+0.17-0.10 Rearth and a 2.17-day orbit in agreement with previous results. We find consistent results for the planet mass from both models: 7.4+/-2.2 Mearth from the GP regression, and 8.0+/-1.6 Mearth from the FCO technique, which implies that this planet is a super-Earth. The planet parameters put planet b in the middle of, or just below, the gap of the radius distribution of small planets. The density is consistent with a rocky composition of primarily iron and magnesium silicate. In agreement with theoretical predictions, we find that the planet is a remnant core, stripped of its atmosphere, and is one of the largest planets found that has lost its atmosphere.

Techniques: radial velocities

Techniques: photometric

Stars: individual: K2-216

Planets and satellites: Atmospheres

Planetary systems

Planets and satellites: composition

Författare

Carina Persson

Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik, Galaktisk astrofysik

Malcolm Fridlund

Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik, Galaktisk astrofysik

O. Barragan

Organisation okänd

F. Dai

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D. Gandolfi

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A. P. Hatzes

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T. Hirano

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S. Grziwa

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J. Korth

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J. Prieto-Arranz

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L. Fossati

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V. Van Eylen

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A. Bo Justesen

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J. Livingston

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D. Kubyshkina

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H. J. Deeg

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E. W. Guenther

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G. Nowak

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J. Cabrera

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Ph Eigmüller

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Sz. Csizmadia

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A. M. S. Smith

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A. Erikson

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S. Albrecht

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R. Alonso

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W. D. Cochran

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M. Endl

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M. Esposito

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A. Fukui

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P. Heeren

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D. Hidalgo

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M. Hjorth

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M. Kuzuhara

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N. Narita

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D. Nespral

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E. Palle

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M. Pätzold

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H. Rauer

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F. Rodler

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J. N. Winn

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Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 618 33

Exoplaneter från rymden - CHEOPS och PLATO

Rymdstyrelsen, 2017-01-01 -- 2022-12-31.

Ämneskategorier

Astronomi, astrofysik och kosmologi

Fundament

Grundläggande vetenskaper

Infrastruktur

Onsala rymdobservatorium

DOI

10.1051/0004-6361/201832867

Mer information

Senast uppdaterat

2018-10-30