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

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 Mb = 16.6 ± 1.3 M⊕, a radius of Rb = 4.71 ± 0.17 R⊕, and an orbital period of Porb ≃ 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 (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 atmosphericmetal-to-hydrogen content and thermal structure could provide us with important clues on the formation mechanisms of this class of objects.

P. J. Wheatley | L. Fossati | A. Erikson | I. Ribas | F. Faedi | W. D. Cochran | M. Endl | D. Pollacco | S. Udry | H. Rauer | M. Deleuil | A. S. Bonomo | P. Figueira | A. P. Hatzes | S. G. Sousa | X. Dumusque | G. Nowak | P. E. Cubillos | D. Barrado | O. Demangeon | N. C. Santos | M. Fridlund | T. Hirano | J. Cabrera | David J Armstrong | M. N. Lund | F. Bouchy | D. Bayliss | D. Gandolfi | P. Eigmuller | J. Lillo-Box | V. Van Eylen | S. Hojjatpanah | D. Hidalgo | F. Meru | S. Mathur | S. Redfield | N. Narita | E. W. Guenther | M. Esposito | D. Bayliss | F. Bouchy | V. Adibekyan | S. Barros | A. Bonomo | M. Deleuil | O. Demangeon | R. D'iaz | N. Santos | S. Udry | S. Csizmadia | F. Meru | G. Nowak | X. Dumusque | P. Figueira | J. Lillo-Box | E. Pall'e | S. Sousa | W. Cochran | M. Endl | J. Winn | M. Lund | D. Barrado | D. Pollacco | S. Mathur | D. Gandolfi | H. Rauer | A. Erikson | A. Hatzes | V. V. Eylen | A. Fukui | I. Ribas | F. Dai | T. Hirano | N. Narita | J. Livingston | P. Eigmuller | P. Wheatley | S. Grziwa | J. Cabrera | J. D. Leon | H. Deeg | M. Fridlund | E. Guenther | J. Korth | D. Nespral | C. Persson | J. Prieto-arranz | F. Faedi | H. Osborn | M. Patzold | R. Luque | D. Hidalgo | R. Alonso | S. Redfield | A. B. Justesen | M. Hjorth | P. Beck | E. Knudstrup | K. Lam | P. Niraula | L. Fossati | O. Barrag'an | P. Cubillos | R. Luque | J. N. Winn | D. J. Armstrong | H. P. Osborn | S.C.C. Barros | E. Bryant | B. Cooke | L. Nielsen | A.M.S. Smith | E. Delgado Mena | E. Pall'e | M. Patzold | M. Esposito | S. Hojjatpanah | Dja Brown | H. Deeg | P. Beck | R. F. D'iaz | V. Adibekyan | E. D. Mena | P. Niraula | J. H. Livingston | O. Barrag'an | B. Cooke | F. Dai | L. D. Nielsen | C. M. Persson | M. M. Musso | R. Alonso | D.J.A. Brown | E. Bryant | S. Csizmadia | A. Fukui | S. Grziwa | M. Hjorth | E. Knudstrup | J. Korth | K.W.F. Lam | J. de Leon | P. Montan'es Rodr'iguez | D. Nespral | J. Prieto-Arranz | A.M.S. Smith | M. Tala-Pinto | P. M. Rodr'iguez | M. Musso | M. Tala-Pinto | A. Smith | J. Prieto-Arranz

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