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

M. Esposito, D. J. Armstrong, D. Gandolfi, V. Zh. Adibekyan, M. Fridlund, N. C. Santos, E. Delgado Mena, L. Fossati, J. Lillo Box, D. Barrado, R. F. Díaz, P. J. Wheatley, A. Hatzes, V. Van Eylen, R. Alonso, P. G. Beck, S. C. C. Barros, D. Bayliss, A. S. Bonomo, F. Bouchy, D. Brown, J. Cabrera, W. D. Cochran, Sz. Csizmadia, H. J. 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, T. Hirano, S. Hojjatpanah, J. Korth, K. W. F. Lam, M. N. Lund, S. Mathur, P. Montañés Rodríguez, H. P. Osborn, E. Pallé, M. Pätzold, D. Pollacco, J. Prieto-Arranz, H. Rauer, I. Ribas, S. G. Sousa, A. M. S. Smith, S. Udry, J. Winn

Abstract

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 RHK = −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.

Keywords
planets and satellites: detection; planets and satellites: fundamental parameters; techniques: radial velocities; stars: fundamental parameters; techniques: photometric; planets and satellites: individual: HD 219666 b

Astronomy and Astrophysics
Volume 623, Article Number A165, Number of pages 11
2019 March

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia