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K2-111: an old system with two planets in near-resonance

A. Mortier, M. R. Zapatero-Osorio, L. Malavolta, Y. Alibert, K. Rice, J. Lillo-Box, A. Vanderburg, M. Oshagh, L. A. Buchhave, V. Zh. Adibekyan, E. Delgado Mena, M. López-Morales, D. Charbonneau, S. G. Sousa, C. Lovis, L. Affer, C. Allende Prieto, S. C. C. Barros, S. Benatti, A. S. Bonomo, W. Boschin, F. Bouchy, A. Cabral, A. Collier Cameron, R. Cosentino, S. Cristiani, O. Demangeon, P. Di Marcantonio, V. D'Odorico, X. Dumusque, D. Ehrenreich, P. Figueira, A. F. M. Fiorenzano, A. Ghedina, J. I. González Hernández, J. Haldemann, A. Harutyunyan, M. Haywood, D. W. Latham, B. Lavie, G. Lo Curto, J. Maldonado, A. Manescau, C. J. A. P. Martins, M. Mayor, D. Mégevand, A. Mehner, G. Micela, P. Molaro, E. Molinari, N. J. Nunes, F. Pepe, E. Pallé, D. F. Phillips, G. Piotto, M. Pinamonti, E. Poretti, M. Riva, R. Rebolo López, N. C. Santos, D. Sasselov, A. Sozzetti, A. Suárez Mascareño, S. Udry, R. G. West, C. A. Watson, T. G. Wilson

Abstract
This paper reports on the detailed characterization of the K2-111 planetary system with K2, WASP, and ASAS-SN photometry, as well as high-resolution spectroscopic data from HARPS-N and ESPRESSO. The host, K2-111, is confirmed to be a mildly evolved (log g = 4.17), iron-poor ([Fe/H] = −0.46), but alpha-enhanced ([α/Fe]=0.27), chromospherically quiet, very old thick disc G2 star. A global fit, performed by using PyORBIT, shows that the transiting planet, K2-111 b, orbits with a period Pb = 5.3518 ± 0.0004 d and has a planet radius of 1.82+0.11−0.09 R and a mass of 5.29+0.76−0.77 M, resulting in a bulk density slightly lower than that of the Earth. The stellar chemical composition and the planet properties are consistent with K2-111 b being a terrestrial planet with an iron core mass fraction lower than the Earth. We announce the existence of a second signal in the radial velocity data that we attribute to a non-transiting planet, K2-111 c, with an orbital period of 15.6785 ± 0.0064 d, orbiting in near-3:1 mean motion resonance with the transiting planet, and a minimum planet mass of 11.3 ± 1.1 M. Both planet signals are independently detected in the HARPS-N and ESPRESSO data when fitted separately. There are potentially more planets in this resonant system, but more well-sampled data are required to confirm their presence and physical parameters.

Keywords
techniques: photometric; techniques: radial velocities; techniques: spectroscopic; planets and satellites: detection; stars: individual (K2-111); Astrophysics - Earth and Planetary Astrophysics

Notes
Based on Guaranteed Time Observations collected at the European Southern Observatory under ESO programmes 1102.C-0744 and 1104.C-0350 by the ESPRESSO Consortium and at the Italian Telescopio Nazionale Galileo (TNG) by the HARPS-N Collaboration.

Monthly Notices of the Royal Astronomical Society
Volume 499, Issue 4, Page 5004
2020 December

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