3 years ago

# EPIC 210897587: A Bright Metal-Poor M Dwarf with Three Transiting Super-Earths.

Artie P. Hatzes, Szilard Csizmadia, Seth Redfield, Vincent Van Eylen, Yuka Fujii, Anders Erikson, Fei Dai, Ignasi Ribas, Carina M. Persson, Alexis M. S. Smith, Davide Gandolfi, Sascha Grziwa, Simon Albrecht, Michael Endl, John H. Livingston, Joshua N. Winn, Philipp Eigmüller, Oscar Barragan, William D. Cochran, Judith Korth, Martin Pätzold, Prajwal Niraula, Hans Deeg, Eike W. Guenther, Juan Cabrera, Jorge Prieto-Arranz, Teruyuki Hirano, Grzegorz Nowak, David Nespral, Heike Rauer, Enric Palle, Malcolm Fridlund, P. Wilson Cauley, Norio Narita, Akihiko Fukui

We report on the discovery of three transiting super-Earths around EPIC 210897587, a relatively bright early M dwarf ($V=12.81$ mag) observed during Campaign 13 of the NASA {\it K2} mission. To characterize the system and validate the planet candidates, we conducted speckle imaging and high-dispersion optical spectroscopy, including radial velocity measurements. Based on the {\it K2} light curve and the spectroscopic characterization of the host star, the planet sizes and orbital periods are $1.55_{-0.17}^{+0.20}\,R_\oplus$ and $6.34365\pm 0.00028$ days for the inner planet; $1.95_{-0.22}^{+0.27}\,R_\oplus$ and $13.85402\pm 0.00088$ days for the middle planet; and $1.64_{-0.17}^{+0.18}\,R_\oplus$ and $40.6835\pm 0.0031$ days for the outer planet. The outer planet (EPIC 210897587.3) is near the habitable zone, with an insolation $1.67\pm 0.38$ times that of the Earth. The planet's radius falls within the range between that of smaller rocky planets and larger gas-rich planets. To assess the habitability of this planet, we present a series of 3D global climate simulations assuming that EPIC 210897587.3 is tidally locked and has an Earth-like composition and atmosphere. We find that the planet can maintain a moderate surface temperature if the insolation proves to be smaller than $\sim 1.5$ times that of the Earth. Doppler mass measurements, transit spectroscopy, and other follow-up observations should be rewarding, since EPIC 210897587 is one of the optically brightest M dwarfs known to harbor transiting planets.

Publisher URL: http://arxiv.org/abs/1801.06957

DOI: arXiv:1801.06957v1

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