K2-111: an old system with two planets in near-resonance
Creators: name: Mortier, A.
name: Osorio, M. R. Zapatero
name: Malavolta, L.
name: Alibert, Y.
name: Rice, K.
name: Lillo-Box, J.
name: Vanderburg, A.
name: Oshagh, M.
name: Buchhave, L.
name: Adibekyan, V.
name: Mena, E. Delgado
name: Lopez-Morales, M.
name: Charbonneau, D.
name: Sousa, S. G.
name: Lovis, C.
name: Affer, L.
name: Prieto, C. Allende
name: Barros, S. C. C.
name: Benatti, S.
name: Bonomo, A. S.
name: Boschin, W.
name: Bouchy, F.
name: Cabral, A.
name: Cameron, A. Collier
name: Cosentino, R.
name: Cristiani, S.
name: Demangeon, O. D. S.
name: Di Marcantonio, P.
name: D'Odorico, V.
name: Dumusque, X.
name: Ehrenreich, D.
name: Figueira, P.
name: Fiorenzano, A.
name: Ghedina, A.
name: Hernández, J. I. González
name: Haldemann, J.
name: Harutyunyan, A.
name: Haywood, R. D.
name: Latham, D. W.
name: Lavie, B.
name: Curto, G. Lo
name: Maldonado, J.
name: Manescau, A.
name: Martins, C. J. A. P.
name: Mayor, M.
name: Mégevand, D.
name: Mehner, A.
name: Micela, G.
name: Molaro, P.
name: Molinari, E.
name: Nunes, N. J.
name: Pepe, F. A.
name: Palle, E.
name: Phillips, D.
name: Piotto, G.
name: Pinamonti, M.
name: Poretti, E.
name: Riva, M.
name: Rebolo, R.
name: Santos, N. C.
name: Sasselov, D.
name: Sozzetti, A.
name: Mascareño, A. Suárez
name: Udry, S.
name: West, R. G.
name: Watson, C. A.
name: Wilson, T. G.
Publisher: name: arXiv
Year: 2020
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: This paper reports on the detailed characterisation 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, K2-111b, orbits with a period $P_b=5.3518\pm0.0004$ d, and has a planet radius of $1.82^{+0.11}_{-0.09}$ R$_\oplus$ and a mass of $5.29^{+0.76}_{-0.77}$ M$_\oplus$, resulting in a bulk density slightly lower than that of the Earth. The stellar chemical composition and the planet properties are consistent with K2-111b 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, K2-111c, with an orbital period of $15.6785\pm 0.0064$ days, orbiting in near-3:1 mean-motion resonance with the transiting planet, and a minimum planet mass of $11.3\pm1.1$ M$_\oplus$. 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.
description: Accepted for publication in MNRAS on 28 Sept 2020. Paper is 18 pages with an additional 12 pages of supplementary material. Data is available at https://vizier.u-strasbg.fr/viz-bin/VizieR?-source=J/MNRAS/499/5004