@article{860e0d6ebfa94351a09c9d7a7f698809,
title = "Super-Earth of 8 M⊕ in a 2.2-day orbit around the K5V star K2-216",
abstract = "Context. 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. Aims. Our aim was to confirm the detection and derive the main physical characteristics of K2-216 b, including the mass. Methods. We performed a series of follow-up observations: high-resolution imaging with the FastCam camera at the TCS and the Infrared Camera and Spectrograph at Subaru, and high-resolution spectroscopy with HARPS (La Silla), HARPS-N (TNG), and FIES (NOT). The stellar spectra were analyzed with the SpecMatch-Emp and SME codes to derive the fundamental stellar 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 so-called floating chunk offset (FCO) technique to simultaneously model the planetary signal and correlated noise associated with stellar activity. Results. 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 M⊕ and radius 0.72 ± 0.03 R⊕. Planet b is found to have a radius of 1.75-0.10 +0.17 R⊕ and a 2.17-day orbit in agreement with previous results. We find consistent results for the planet mass from both models: Mp ≈ 7.4 ± 2.2 M⊕ from the GP regression and Mp ≈ 8.0 ± 1.6 M⊕ from the FCO technique, which implies that this planet is a super-Earth. The incident stellar flux is 2.48-48 +220 F⊕. Conclusions. 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.",
keywords = "Planetary systems, Planets and satellites: Atmospheres, Planets and satellites: composition, Stars: individual: K2-216, Techniques: photometric, Techniques: radial velocities",
author = "Persson, {C. M.} and M. Fridlund and O. Barrag{\'a}n and F. Dai and D. Gandolfi and Hatzes, {A. P.} and T. Hirano and S. Grziwa and J. Korth and J. Prieto-Arranz and L. Fossati and {Van Eylen}, V. and Justesen, {A. B.} and J. Livingston and D. Kubyshkina and Deeg, {H. J.} and Guenther, {E. W.} and G. Nowak and J. Cabrera and Ph Eigm{\"o}ller and Sz Csizmadia and Smith, {A. M.S.} and A. Erikson and S. Albrecht and Alonso Sobrino and Cochran, {W. D.} and M. Endl and M. Esposito and A. Fukui and P. Heeren and D. Hidalgo and M. Hjorth and M. Kuzuhara and N. Narita and D. Nespral and E. Palle and M. P{\"a}tzold and H. Rauer and F. Rodler and Winn, {J. N.}",
note = "Funding Information: Acknowledgements. We thank the NOT, TNG, ESO, Subaru, and TCS staff members for their support during the observations. Based on observations obtained with (a) the Nordic Optical Telescope (NOT), operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos (ORM) of the Instituto de Astrod{\'i}sica de Canarias (IAC) (programmes 53-016, 54-027, and 54-211); (b) with the Italian Telescopio Nazionale Galileo (TNG) operated at the ORM (IAC) on the island of La Palma by the INAF Fundaci{\'o}n Galileo Galilei (programmes CAT16B_61, CAT17A_91, A36TAC_12, and OPT17B_59); (c) the 3.6 m ESO telescope at La Silla Observatory (programmes 098.C-0860, 099.C-0491 and 0100.C-0808); (d) the Telescopio Carlos S{\'a}nchez (TCS) installed at IAC{\textquoteright}s Observatorio del Teide, Tenerife; (e) the Subaru Telescope, operated by the National Astronomical Observatory of Japan; (f) NESSI, funded by the NASA Exoplanet Exploration Program and the NASA Ames Research Center. NESSI was built at the Ames Research Center by Steve B. Howell, Nic Scott, Elliott P. Horch, and Emmett Quigley; (g) the K2/Kepler mission. Funding for the K2/Kepler mission is provided by the NASA Science Mission Directorate. The K2 data presented in this paper were downloaded from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX13AC07G and by other grants and contracts. This work has made use of SME package, which benefits from the continuing development work by J. Valenti and N. Piskunov and we gratefully acknowledge their continued support. This work has made use of the VALD database, operated at Uppsala University, the Institute of Astronomy RAS in Moscow, and the University of Vienna (Kupka et al. 2000; Ryabchikova et al. 2015). C.M.P. and M.F. gratefully acknowledge the support of the Swedish National Space Board. D.G. gratefully acknowledges the financial support of the Programma Giovani Ricercatori – Rita Levi Montal-cini – Rientro dei Cervelli (2012) awarded by the Italian Ministry of Education, Universities and Research (MIUR). D.K. and L.F. acknowledge the Austrian Funding Information: Forschungs-f{\"o}rderungsgesellschaft FFG project “TAPAS4CHEOPS” P853993. Sz.C, A.P.H., M.P., and H.R. acknowledge the support of the DFG priority programme SPP 1992 “Exploring the Diversity of Extrasolar Planets” (HA 3279/12-1, PA525/18-1, PA525/19-1, PA525/20-1, and RA 714/14-1). Funding for the Stellar Astrophysics Centre is provided by the Danish National Research Foundation (grant agreement No. DNRF106). This project has received funding from the European Union{\textquoteright}s Horizon 2020 research and innovation programme under grant agreement No. 730890. This material reflects only the authors views and the Commission is not liable for any use that may be made of the information contained therein. We thank the anonymous referee whose constructive comments led to an improvement of the paper. Publisher Copyright: {\textcopyright} ESO 2018.",
year = "2018",
month = oct,
day = "1",
doi = "10.1051/0004-6361/201832867",
language = "English (US)",
volume = "618",
journal = "Astronomy and Astrophysics",
issn = "0004-6361",
publisher = "EDP Sciences",
}