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. Buchhave, V. Adibekyan, E. Delgado Mena, M. Lopez-Morales, D. Charbonneau, S. G. Sousa, C. Lovis, L. Affer, C. Allende Prieto, S. C. C. Barros, S. Benatti, A. S. BonomoW. Boschin, F. Bouchy, A. Cabral, A. Collier Cameron, R. Cosentino, S. Cristiani, O. D. S. Demangeon, P. Di Marcantonio, V. D'Odorico, X. Dumusque, D. Ehrenreich, P. Figueira, A. Fiorenzano, A. Ghedina, J. I. González Hernández, J. Haldemann, A. Harutyunyan, R. D. 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. A. Pepe, E. Palle, D. Phillips, G. Piotto, M. Pinamonti, E. Poretti, M. Riva, R. Rebolo, N. C. Santos, D. Sasselov, A. Sozzetti, A. Suárez Mascareño, S. Udry, R. G. West, C. A. Watson, T. G. Wilson

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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 theEarth. 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.
Original languageEnglish
Pages (from-to)5004-5021
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 27 Oct 2020
Externally publishedYes


  • techniques: photometric
  • techniques: radial velocities
  • techniques: spectroscopic
  • planets and satellites: detection
  • stars: individual (K2-111)


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