Peering into the young planetary system AB Pic
Astronomy and Astrophysics, vol. 670, pp. A90
Abstract
Aims . We aim to revisit the formation pathway of AB Pic b, an imaged companion that straddles the exoplanet/brown-dwarf boundary. We based this study on a rich set of observations, which allows us to investigate its orbital and atmospheric properties. Methods . We composed a spectrum of AB Pic b by merging archival medium-resolution (~4000) VLT/SINFONI K band (1.96–2.45 µm) data with published spectra at J and H bands from SINFONI, Lp band from Magellan-AO/CLIO2, and photometric measurements from HST (visible) and Spitzer (mid-infrared). We modeled the spectrum with ForMoSA, following a forward-modeling approach based on two atmospheric models: ExoREM and BT-SETTL13. In parallel, we determined the orbital properties of AB Pic b fitting orbital solutions to astrometric measurements from NaCo (2003 and 2004) and SPHERE (2015). Results . The orbital solutions favor a semi-major axis of 190 -50 +200 au on a highly inclined orbit (edge-on), but with a poorly constrained eccentricity. From the atmospheric modeling with Exo-REM, we derive an effective temperature of 1700 ± 50 K and surface gravity of 4.5 ± 0.3 dex, which are consistent with previous findings, and we report for the first time a c/o ratio of 0.58 ± 0.08, consistent with the value for the Sun. The posteriors are sensitive to the wavelength interval and the family of models used. Given the published rotation period of 2.1 h and our derived υ sin( i ) of 73 -27 +11 km s −1 , we estimate for the first time the true obliquity of AB Pic b to be between 45 and 135 deg, indicating a rather significant misalignment between the spin and orbit orientations of the planet. Finally, the existence of a proper-motion anomaly between the H IPPARCOS and Gaia Early Data Release 3 compared to our SPHERE detection limits and adapted radial velocity limits indicates the potential existence of a ~6 M Jup inner planet orbiting from 2 to 10 au (40–200 mas). Conclusions . The possible existence of an inner companion and the likely misalignment of the spin-axis orientation strongly favor a formation path by gravitational instability or core accretion within a protoplanetary disk at a smaller orbital radius followed by a dynamical interaction which scattered AB Pic b to its current location. Confirmation and characterization of this unseen inner exoplanet and access to a broader wavelength coverage and higher spectral resolution for the characterization of AB Picb will be essential for probing the uncertainties associated with the atmospheric and orbital parameters.
Authors 27
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Centre National de la Recherche Scientifique · Université Côte d'Azur · Lagrange Laboratory · Observatoire de la Côte d’Azur · University of Chile
Affiliation as printed
Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
Laboratoire Lagrange, Université Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, 06304 Nice, France
Unidad Mixta Internacional Franco-Chilena de Astronomía, CNRS/INSU UMI 3386, and Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
Laboratoire Lagrange, Université Côte d'Azur, CNRS, Observatoire de la Côte d'Azur, 06304 Nice, France
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Centre National de la Recherche Scientifique · Université Côte d'Azur · Institut de Planétologie et d'Astrophysique de Grenoble · Lagrange Laboratory · Observatoire de la Côte d’Azur · University of Chile · Université Grenoble Alpes
Affiliation as printed
Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
Laboratoire Lagrange, Université Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, 06304 Nice, France
Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
Laboratoire Lagrange, Université Côte d'Azur, CNRS, Observatoire de la Côte d'Azur, 06304 Nice, France
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Centre National de la Recherche Scientifique · Institut de Planétologie et d'Astrophysique de Grenoble · Université Grenoble Alpes
Affiliation as printed
Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
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Centre National de la Recherche Scientifique · University of Chile
Affiliation as printed
Unidad Mixta Internacional Franco-Chilena de Astronomía, CNRS/INSU UMI 3386, and Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
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Centre National de la Recherche Scientifique · Institut de Planétologie et d'Astrophysique de Grenoble · Millenium Nucleus for Planet Formation · University of Valparaíso · Université Grenoble Alpes
Affiliation as printed
Núcleo Milenio Formación Planetaria – NPF, Universidad de Valparaíso, Av. Gran Bretaña 1111, Valparaíso, Chile
Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
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Affiliation as printed
Cornell Center for Astrophysics and Planetary Science, Department of Astronomy, Cornell University, Ithaca, NY 14853, USA
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Lyon 1 Université · École Normale Supérieure de Lyon · Centre National de la Recherche Scientifique · Centre de Recherche Astrophysique de Lyon
Affiliation as printed
Univ Lyon, ENS de Lyon, Univ Lyon 1, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, 69007 Lyon, France
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Lyon 1 Université · École Normale Supérieure de Lyon · Centre National de la Recherche Scientifique · Centre de Recherche Astrophysique de Lyon
Affiliation as printed
Univ Lyon, ENS de Lyon, Univ Lyon 1, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, 69007 Lyon, France
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Centre National de la Recherche Scientifique · Université Paris Sciences et Lettres · Observatoire de Paris · Sorbonne Université · Laboratoire d’études spatiales et d’instrumentation en astrophysique
Affiliation as printed
LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
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Centre National de la Recherche Scientifique · Max Planck Institute for Astronomy · Institut de Planétologie et d'Astrophysique de Grenoble · Université Grenoble Alpes
Affiliation as printed
Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
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Affiliation as printed
Aperio Software Ltd., Insight House, Riverside Business Park, Stoney Common Road, Stansted, Essex, CM24 8PL, UK
Förderkreis Planetarium Göttingen, Göttingen, Germany
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Centre National de la Recherche Scientifique · Université Paris Sciences et Lettres · Observatoire de Paris · Sorbonne Université · Laboratoire d’études spatiales et d’instrumentation en astrophysique
Affiliation as printed
LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
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Centre National de la Recherche Scientifique · Aix-Marseille Université
Affiliation as printed
Aix-Marseille Univ., CNRS, CNES, LAM, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
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Centre National de la Recherche Scientifique · Université Paris Sciences et Lettres · Observatoire de Paris · Sorbonne Université · Laboratoire d’études spatiales et d’instrumentation en astrophysique
Affiliation as printed
LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
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Centre National de la Recherche Scientifique · Université Paris Sciences et Lettres · Observatoire de Paris · Sorbonne Université · Laboratoire d’études spatiales et d’instrumentation en astrophysique
Affiliation as printed
LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
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Centre National de la Recherche Scientifique · Université Paris Sciences et Lettres · Observatoire de Paris · Sorbonne Université · Institut de Planétologie et d'Astrophysique de Grenoble · Laboratoire d’études spatiales et d’instrumentation en astrophysique · Université Grenoble Alpes
Affiliation as printed
LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
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Centre National de la Recherche Scientifique · Institut de Planétologie et d'Astrophysique de Grenoble · Université Grenoble Alpes
Affiliation as printed
Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
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Osservatorio Astronomico di Padova · National Institute for Astrophysics
Affiliation as printed
INAF – Osservatorio Astronomico di Padova, Vicolo dell’ Osservatorio 5, 35122 Padova, Italy
INAF – Osservatorio Astronomico di Padova, Vicolo dell' Osservatorio 5, 35122 Padova, Italy
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Max Planck Institute for Astronomy
Affiliation as printed
Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University, 2300 RA Leiden, The Netherlands
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Osservatorio Astronomico di Padova · National Institute for Astrophysics
Affiliation as printed
INAF – Osservatorio Astronomico di Padova, Vicolo dell’ Osservatorio 5, 35122 Padova, Italy
INAF – Osservatorio Astronomico di Padova, Vicolo dell' Osservatorio 5, 35122 Padova, Italy
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Centre National de la Recherche Scientifique · Institut de Planétologie et d'Astrophysique de Grenoble · Université Grenoble Alpes
Affiliation as printed
Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
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University of Michigan · ETH Zurich · Institute for Particle Physics and Astrophysics
Affiliation as printed
Department of Astronomy, University of Michigan, 1085 S. University Ave, Ann Arbor, MI 48109, USA
Institute for Particle Physics and Astrophysics, ETH Zürich, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland
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Osservatorio Astronomico di Padova · National Institute for Astrophysics
Affiliation as printed
INAF – Osservatorio Astronomico di Padova, Vicolo dell’ Osservatorio 5, 35122 Padova, Italy
INAF – Osservatorio Astronomico di Padova, Vicolo dell' Osservatorio 5, 35122 Padova, Italy
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University, 2300 RA Leiden, The Netherlands
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Centre National de la Recherche Scientifique · Aix-Marseille Université
Affiliation as printed
Aix-Marseille Univ., CNRS, CNES, LAM, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University, 2300 RA Leiden, The Netherlands
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