HD 219666 b: a hot-Neptune from TESS Sector 1

ESPOSITO, M.; ARMSTRONG, D.J.; GANDOLFI, D.; ADIBEKYAN, V.; FRIDLUND, M.; SANTOS, N.C.; LIVINGSTON, J.H.; DELGADO MENA, E.; FOSSATI, L.; LILLO-BOX, J.; BARRAGÁN, O.; BARRADO, D.; CUBILLOS, P.E.; COOKE, B.; JUSTESEN, A.B.; MERU, F.; DÍAZ, R.F.; DAI, F.; NIELSEN, L.D.; PERSSON, C.M.; WHEATLEY, P.J.; HATZES, A.P.; VAN EYLEN, V.; MUSSO, M.M.; ALONSO, R.; BECK, P.G.; BARROS, S.C.C.; BAYLISS, D.; BONOMO, A.S.; BOUCHY, F.; BROWN, D.J.A.; BRYANT, E.; CABRERA, J.; COCHRAN, W.D.; CSIZMADIA, S.; DEEG, H.; DEMANGEON, O.; DELEUIL, M.; DUMUSQUE, X.; EIGMÜLLER, P.; ENDL, M.; ERIKSON, A.; FAEDI, F.; FIGUEIRA, P.; FUKUI, A.; GRZIWA, S.; GUENTHER, E.W.; HIDALGO, D.; HJORTH, M.; HIRANO, T.; HOJJATPANAH, S.; KNUDSTRUP, E.; KORTH, J.; LAM, K.W.F.; DE LEON, J.; LUND, M.N.; LUQUE, R.; MATHUR, S.; MONTAÑÉS RODRÍGUEZ, P.; NARITA, N.; NESPRAL, D.; NIRAULA, P.; NOWAK, G.; OSBORN, H.P.; PALLÉ, E.; PÄTZOLD, M.; POLLACCO, D.; PRIETO-ARRANZ, J.; RAUER, H.; REDFIELD, S.; RIBAS, I.; SOUSA, S.G.; SMITH, A.M.S.; TALA-PINTO, M.; UDRY, S.; WINN,

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Año: 2019 vol. 623

0004-6361

We report on the confirmation and mass determination of a transiting planet orbiting the old and inactive G7 dwarf star HD 219666 (M ∗ = 0.92 ± 0.03 M ⊙ , R ∗ = 1.03 ± 0.03 R ⊙ , τ ∗ = 10 ± 2 Gyr). With a mass of M b = 16.6 ± 1.3 M ⊙ , a radius of R b = 4.71 ± 0.17 R ⊙ , and an orbital period of P orb ≃ 6 days, HD 219666 b is a new member of a rare class of exoplanets: the hot-Neptunes. The Transiting Exoplanet Survey Satellite (TESS) observed HD 219666 (also known as TOI-118) in its Sector 1 and the light curve shows four transit-like events, equally spaced in time. We confirmed the planetary nature of the candidate by gathering precise radial-velocity measurements with the High Accuracy Radial velocity Planet Searcher (HARPS) at ESO 3.6 m. We used the co-added HARPS spectrum to derive the host star fundamental parameters (T eff = 5527 ± 65 K, log g ∗ = 4.40 ± 0.11 (cgs), [Fe/H]= 0.04 ± 0.04 dex, log R ′ HK = -5.07 ± 0.03), as well as the abundances of many volatile and refractory elements. The host star brightness (V = 9.9) makes it suitable for further characterisation by means of in-transit spectroscopy. The determination of the planet orbital obliquity, along with the atmosphericmetal-to-hydrogen content and thermal structure could provide us with important clues on the formation mechanisms of this class of objects.