planets and satellites: composition; planets and satellites: fundamental parameters; stars: individual (HD 77946); techniques: photometric; techniques: radial velocities; techniques: spectroscopic; Exo-planets; Neptune; Planetary system; Planets and satellites: compositions; Planets and satellites: fundamental parameters; Star: individual (HD 77946); Stars: individual: proxima Centauri; Techniques: photometric; Techniques: radial velocities; Techniques: spectroscopic; Astronomy and Astrophysics; Space and Planetary Science; astro-ph.EP
Abstract :
[en] We report on the detailed characterization of the HD 77946 planetary system. HD 77946 is an F5 (M∗ = 1.17 M, R∗ = 1.31 R) star, which hosts a transiting planet recently discovered by NASA’s Transiting Exoplanet Survey Satellite (TESS), classified as TOI-1778 b. Using TESS photometry, high-resolution spectroscopic data from HARPS-N, and photometry from CHEOPS, we measure the radius and mass from the transit and radial velocity observations, and find that the planet, HD 77946 b, orbits with period (Formula Presented) d, has a mass of Mb = 8.38 ± 1.32 M, and a radius of (Formula Presented) R. From the combination of mass and radius measurements, and the stellar chemical composition, the planet properties suggest that HD 77946 b is a sub-Neptune with a ∼1 per cent H/He atmosphere. However, a degeneracy still exists between water-world and silicate/iron-hydrogen models, and even though interior structure modelling of this planet favours a sub-Neptune with a H/He layer that makes up a significant fraction of its radius, a water-world composition cannot be ruled out, as with (Formula Presented) K, water may be in a supercritical state. The characterization of HD 77946 b, adding to the small sample of well-characterized sub-Neptunes, is an important step forwards on our journey to understanding planetary formation and evolution pathways. Furthermore, HD 77946 b has one of the highest transmission spectroscopic metrics for small planets orbiting hot stars, thus transmission spectroscopy of this key planet could prove vital for constraining the compositional confusion that currently surrounds small exoplanets.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Palethorpe, L. ; Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, United Kingdom ; Centre for Exoplanet Science, University of Edinburgh, Edinburgh, United Kingdom
John, A. Anna ; SUPA School of Physics and Astronomy, University of St Andrews, St Andrews, United Kingdom ; Centre for Exoplanet Science, University of St Andrews, St Andrews, United Kingdom
Mortier, A. ; School of Physics and Astronomy, University of Birmingham, Birmingham, United Kingdom
Davoult, J. ; Physics Institute, University of Bern, Bern, Switzerland
Wilson, T.G. ; SUPA School of Physics and Astronomy, University of St Andrews, St Andrews, United Kingdom ; Centre for Exoplanet Science, University of St Andrews, St Andrews, United Kingdom
Rice, K. ; Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, United Kingdom ; Centre for Exoplanet Science, University of Edinburgh, Edinburgh, United Kingdom
Cameron, A.C. ; SUPA School of Physics and Astronomy, University of St Andrews, St Andrews, United Kingdom ; Centre for Exoplanet Science, University of St Andrews, St Andrews, United Kingdom
Alibert, Y. ; Physics Institute, University of Bern, Bern, Switzerland ; Center for Space and Habitability, University of Bern, Bern, Switzerland
Buchhave, L.A. ; DTU Space, National Space Institute, Technical University of Denmark, Kgs. Lyngby, Denmark
Malavolta, L. ; Dipartimento di Fisica e Astronomia ‘Galileo Galilei, ’ Universitá di Padova, Padova, Italy
Cadman, J. ; Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, United Kingdom ; Centre for Exoplanet Science, University of Edinburgh, Edinburgh, United Kingdom
López-Morales, M. ; Center for Astrophysics, Harvard & Smithsonian, Cambridge, United States
Dumusque, X. ; Département d’astronomie de l’Université de Genève, Versoix, Switzerland
Silva, A.M. ; Space sciences, Technologies and Astrophysics Research (STAR) Institute, University of Liège, Liège, Belgium ; Observatoire de Genève, University of Geneva, Versoix, Switzerland
Quinn, S.N. ; Center for Astrophysics, Harvard & Smithsonian, Cambridge, United States
Van Eylen, V. ; Mullard Space Science Laboratory, University College London, Surrey, United Kingdom
Vissapragada, S. ; Center for Astrophysics, Harvard & Smithsonian, Cambridge, United States
Affer, L. ; INAF - Osservatorio Astronomico di Palermo, Palermo, Italy
Charbonneau, D. ; Center for Astrophysics, Harvard & Smithsonian, Cambridge, United States
Cosentino, R. ; Fundación Galileo Galilei - INAF, Spain
Ghedina, A. ; Fundación Galileo Galilei - INAF, Spain
Haywood, R.D. ; Astrophysics Group, University of Exeter, Exeter, United Kingdom
Latham, D.W. ; Center for Astrophysics, Harvard & Smithsonian, Cambridge, United States
Lienhard, F. ; Astrophysics Group, Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom
Fiorenzano, A.F. Martínez ; Fundación Galileo Galilei - INAF, Spain
Pedani, M. ; Fundación Galileo Galilei - INAF, Spain
Pepe, F.; Département d’astronomie de l’Université de Genève, Versoix, Switzerland
Pinamonti, M. ; INAF - Osservatorio Astrofisico di Torino, Pino Torinese, Italy
Stalport, Manu ; Université de Liège - ULiège > Unités de recherche interfacultaires > Space sciences, Technologies and Astrophysics Research (STAR)
Udry, S. ; Observatoire de Genève, University of Geneva, Versoix, Switzerland
Vanderburg, A. ; Department of Physics, Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, United States
The HARPS-N project was funded by the Prodex Program of the Swiss Space Office (SSO), the Harvard University Origin of Life Initiative (HUOLI), the Scottish Universities Physics Alliance (SUPA), the University of Geneva, the Smithsonian Astrophysical Observatory (SAO), the Italian National Astrophysical Institute (INAF), University of St. Andrews, Queen\u2019s University Belfast, and University of Edinburgh. We thank Suzanne Aigrain for her work in obtaining observations. MPi acknowledges the financial support from the ASI-INAF Addendum n.2018-24-HH.1-2022 \u2018Partecipazione italiana al Gaia DPAC \u2013 Operazioni e attivit\u00E0 di analisi dati\u2019. ACC and TW acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1. KR acknowledges support from STFC Consolidated grant number ST/V000594/1. AAJ acknowledges support from a World-Leading St Andrews Doctoral Scholarship. This work has been carried out within the framework of the NCCR PlanetS supported by the Swiss National Science Foundation under grants 51NF40 182901 and 51NF40 205606. RDH is funded by the UK Science and Technology Facilities Council (STFC)\u2019s Ernest Rutherford Fellowship (grant number ST/V004735/1). FPE would like to acknowledge the Swiss National Science Foundation (SNSF) for supporting research with HARPS-N through the SNSF grants nr. 140649, 152721, 166227, and 184618. The HARPS-N Instrument Project was partially funded through the Swiss ESA-PRODEX Programme. This work has been carried out within the framework of the NCCR PlanetS supported by the Swiss National Science Foundation under grants 51NF40 182901 and 51NF40 205606. This project has received funding from the European Research Council (ERC) under the European Union\u2019s Horizon 2020 research and innovation programme (grant agreement SCORE No 851555). This research has made use of data obtained from or tools provided by the portal exoplanet.eu of The Extrasolar Planets Encyclopaedia.ACC and TW acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1. KR acknowledges support from STFC Consolidated grant number ST/V000594/1.This work has been carried out within the framework of the NCCR PlanetS supported by the Swiss National Science Foundation under grants 51NF40_182901 and 51NF40_205606. This project has received funding from the European Research Council (ERC) under the European Union\u2019s Horizon 2020 research and innovation programme (grant agreement SCORE No 851555).This work has been carried out within the framework of the NCCR PlanetS supported by the Swiss National Science Foundation under grants 51NF40_182901 and 51NF40_205606.RDH is funded by the UK Science and Technology Facilities Council (STFC)\u2019s Ernest Rutherford Fellowship (grant number ST/V004735/1).
Commentary :
19 pages, 13 figures, 5 tables. Published in MNRAS
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