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

¹ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
e-mail: mesposito@tls-tautenburg.de
² Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK
³ Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK
⁴ Dipartimento di Fisica, Università degli Studi di Torino, via Pietro Giuria 1, 10125 Torino, Italy
⁵ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁶ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
⁷ Leiden Observatory, University of Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
⁸ Departamento de Física e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua Campo Alegre, 4169-007 Porto, Portugal
⁹ Department of Astronomy, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan
¹⁰ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8041 Graz, Austria
¹¹ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
¹² Departamento de Astrofísica, Centro de Astrobiología (INTA-CSIC), Campus ESAC (ESA)Camino Bajo del Castillo s/n 28692 Villanueva de la Cañada, Spain
¹³ Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Buenos Aires, Argentina
¹⁴ CONICET – Universidad de Buenos Aires, Instituto de Astronomía y Física del Espacio (IAFE), Buenos Aires, Argentina
¹⁵ Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544, USA
¹⁶ Geneva Observatory, University of Geneva, Chemin des Mailettes 51, 1290 Versoix, Switzerland
¹⁷ Stellar Astrophysics Centre, Deparment of Physics and Astronomy, Aarhus University, Ny Munkegrade 120, 8000 Aarhus C, Denmark
¹⁸ Instituto de Astrofísica de Canarias, C/ Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
¹⁹ Departamento de Astrofísica, Universidad de La Laguna, 38206 Tenerife, Spain
²⁰ Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489 Berlin, Germany
²¹ Department of Astronomy and McDonald Observatory, University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712, USA
²² Department of Physics and Kavli Institute for Astrophysics and Space Research, MIT, Cambridge, MA 02139, USA
²³ Aix-Marseille Université, CNRS, CNES, LAM, Marseille, France
²⁴ National Astronomical Observatory of Japan, NINS, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²⁵ Rheinisches Institut für Umweltforschung an der Universität zu Köln, Aachener Strasse 209, 50931 Köln, Germany
²⁶ Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro-ku, Tokyo, Japan
²⁷ Department of Earth, Atmospheric and Planetary Sciences, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
²⁸ Zentrum für Astronomie und Astrophysik, Technische Universität Berlin, Hardenbergstr. 36 10623 Berlin, Germany
²⁹ Astrobiology Center, NINS, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
³⁰ Astronomy Department and Van Vleck Observatory, Wesleyan University, Middletown, CT 06459, USA
³¹ Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstr. 74–100 12249 Berlin, Germany
³² Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, Bellaterra, Spain
³³ Institut d’Estudis Espacials de Catalunya (IEEC), Barcelona, Spain
³⁴ Landessternwarte Königstuhl, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
³⁵ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
³⁶ JST, PRESTO, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Received: 13 December 2018
Accepted: 4 February 2019

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 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.