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K2-291b: A Rocky Super-Earth in a 2.2 day Orbit

M. R. Kosiarek, S. Blunt, M. López-Morales, I. J. M. Crossfield, E. Sinukoff, E. Petigura, E. J. Gonzales, E. Poretti, L. Malavolta, A. W. Howard, H. Isaacson, R. D. Haywood, D. Ciardi, M. Bristow, A. Collier Cameron, D. Charbonneau, C. D. Dressing, P. Figueira, B. J. Fulton, B. J. Hardee, L. A. Hirsch, D. W. Latham, A. Mortier, C. Nava, J. E. Schlieder, A. Vanderburg, L. M. Weiss, A. S. Bonomo, F. Bouchy, L. A. Buchhave, A. Coffinet, M. Damasso, X. Dumusque, C. Lovis, M. Mayor, G. Micela, E. Molinari, F. Pepe, D. F. Phillips, G. Piotto, K. Rice, D. Sasselov, D. Ségransan, A. Sozzetti, S. Udry, C. A. Watson

Abstract
K2-291 (EPIC 247418783) is a solar-type star with a radius of R* = 0.899 ± 0.034 R and mass of M*=0.934 ± 0.038 M. From K2 C13 data, we found one super-Earth planet (Rp = 1.589+0.095-0.072 R) transiting this star on a short period orbit (P = 2.225177 +6.6e-5 -6.8e-5 days). We followed this system up with adaptive-optic imaging and spectroscopy to derive stellar parameters, search for stellar companions, and determine a planet mass. From our 75 radial velocity measurements using HIRES on Keck I and HARPS-N on Telescopio Nazionale Galileo, we constrained the mass of EPIC 247418783b to Mp = 6.49 ± 1.16 M. We found it necessary to model correlated stellar activity radial velocity signals with a Gaussian process in order to more accurately model the effect of stellar noise on our data; the addition of the Gaussian process also improved the precision of this mass measurement. With a bulk density of 8.84+2.50-2.03 g cm-3, the planet is consistent with an Earth-like rock/iron composition and no substantial gaseous envelope. Such an envelope, if it existed in the past, was likely eroded away by photo-evaporation during the first billion years of the star's lifetime.

Keywords
planets and satellites: composition; planets and satellites: detection; techniques: radial velocities; Astrophysics - Earth and Planetary Astrophysics

The Astronomical Journal
Volume 157, Number 3
2019 March

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia