Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) II. A broadened sodium feature on the ultra-hot giant WASP-76b

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. G. 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. Knudstrup17, J. Korth, K. W. F. Lan, 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 and J. N. Winn. 2019. HD 219666 b: a hot-Neptune from TESS Sector 1 . Astronomy and Astrophysics 623, DOI: 10.1051/0004-6361/201834853

We report on the confirmation and mass determination of a transiting planet orbiting the old and inactive G7 dwarf star HD219666 (M-star = 0.92 +/- 0.03 M-circle dot, R-star = 1.03 +/- 0.03 R-circle dot, tau(star) = 10 +/- 2 Gyr). With a mass of M-b = 16.6 +/- 1.3 M-circle plus, a radius of R-b = 4.71 +/- 0.17 R-circle plus, and an orbital period of P-orb similar or equal to 6 days, HD219666 b 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 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(star) = 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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