HD219666b: A hot-Neptune from TESS Sector 1

M. Esposito, D.J. Armstrong, D. Gandolfi, V. Adibekyan, M. Fridlund, N.C. Santos, J.H. Livingston, E. Delgado Mena, L. Fossati, J. Lillo-Box, O. Barragán, D. Barrado, P.E. Cubillos, B. Cooke, A.B. Justesen, F. Meru, R.F. Díaz, F. Dai, L.D. Nielsen, C.M. Persson, P.J. Wheatley, A.P. Hatzes, V. Van Eylen, M.M. Musso, R. Alonso, P. Beck, S.C.C. Barros, D. Bayliss, A.S. Bonomo, F. Bouchy, D.J.A. Brown, E. Bryant, J. Cabrera, W.D. Cochran, S. Csizmadia, H. Deeg, O. Demangeon, M. Deleuil, X. Dumusque, P. Eigmüller, M. Endl, A. Erikson, F. Faedi, P. Figueira, A. Fukui, S. Grziwa, E.W. Guenther, D. Hidalgo, M. Hjorth, T. Hirano, S. Hojjatpanah, E. Knudstrup, J. Korth, K.W.F. Lam, J. de Leon, M.N. Lund, R. Luque, S. Mathur, P. Montañés Rodríguez, N. Narita, D. Nespral, P. Niraula, G. Nowak, H.P. Osborn, E. Pallé, M. Pätzold, D. Pollacco, J. Prieto-Arranz, H. Rauer, S. Redfield, I. Ribas, S.G. Sousa, A.M.S. Smith, M. Tala-Pinto, S. Udry, J.N. Winn

HD219666b: A hot-Neptune from TESS Sector 1 See arXiv version Accepted for publication in A&A


We report on the confirmation and mass determination of a transiting planet orbiting the old and inactive G7 dwarf star HD219666 (Mstar = 0.92 +/- 0.03 MSun, Rstar = 1.03 +/- 0.03 RSun, tau_star = 10 +/- 2 Gyr). With a mass of Mb = 16.6 +/- 1.3 MEarth, a radius of Rb = 4.71 +/- 0.17 REarth, and an orbital period of P ~ 6 days, HD219666b is a new member of a rare class of exoplanets: the hot-Neptunes. The Transiting Exoplanet Survey Satellite (TESS) observed HD219666 (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 HARPS@ESO3.6m. We used the co-added HARPS spectrum to derive the host star fundamental parameters (Teff = 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 atmospheric metal-to-hydrogen content and thermal structure could provide us with important clues on the formation mechanisms of this class of objects.

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