Mortier, A., Zapatero Osorio, M. R., Malavolta, L., Alibert, Y., Rice, K., Lillo-Box, J., Vanderburg, A., Oshagh, M., Buchhave, Lars, Adibekyan, V., Delgado Mena, E., Lopez-Morales, Mercedes, Charbonneau, David, Sousa, S. G., Lovis, C., Affer, L., Allende Prieto, C., Barros, S. C. C., Benatti, S., Bonomo, A. S., Boschin, W., Bouchy, F., Cabral, A., Collier Cameron, A., Cosentino, R. et al. 2020. "K2-111: an old system with two planets in near-resonance." Monthly Notices of the Royal Astronomical Society, 499 5004–5021. https://doi.org/10.1093/mnras/staa3144.
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 ([a/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.
