K2-110 b: A massive mini-Neptune exoplanet

OSBORN, H.P.; SANTERNE, A.; BARROS, S.C.C.; SANTOS, N.C.; DUMUSQUE, X.; MALAVOLTA, L.; ARMSTRONG, D.J.; HOJJATPANAH, S.; DEMANGEON, O.; ADIBEKYAN, V.; ALMENARA, J.-M.; BARRADO, D.; BAYLISS, D.; BOISSE, I.; BOUCHY, F.; BROWN, D.J.A.; CAMERON, A.C.; CHARBONNEAU, D.; DELEUIL, M.; DELGADO MENA, E.; DIÁZ, R.F.; HÉBRARD, G.; KIRK, J.; KING, G.W.; LAM, K.W.F.; LATHAM, D.; LILLO-BOX, J.; LOUDEN, T.M.; LOVIS, C.; MARMIER, M.; MCCORMAC, J.; MOLINARI, E.; PEPE, F.; POLLACCO, D.; SOUSA, S.G.; UDRY, S.; WALKER, S.R.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Año: 2017 vol. 604

0004-6361

We report the discovery of the exoplanet K2-110 b (previously EPIC212521166b) from K2 photometry orbiting in a 13.8637d period around an old, metal-poor K3 dwarf star. With a V-band magnitude of 11.9, K2-110 is particularly amenable to RV follow-up. A joint analysis of K2 photometry and high-precision RVs from 28 HARPS and HARPS-N spectra reveal it to have a radius of 2.6 ± 0.1Râ?? and a mass of 16.7 ± 3.2Mâ??, hence a density of 5.2 ± 1.2 g cm-3, making it one of the most massive planets yet to be found with a sub-Neptune radius. When accounting for compression, the resulting Earth-like density is best fitted by a 0.2Mâ?? hydrogen atmosphere over an 16.5Mâ?? Earth-like interior, although the planet could also have significant water content. At 0.1 AU, even taking into account the old stellar age of 8 ± 3 Gyr, the planet is unlikely to have been significantly affected by EUV evaporation. However the planet likelydisc-migrated to its current position making the lack of a thick H2 atmosphere puzzling. This analysis has made K2-110 b one of the best-characterised mini-Neptunes with density constrained to less than 30%.