Letter to the Editor

An imaged 15 M_Jup companion within a hierarchical quadruple system^⋆

¹ LESIA, Observatoire de Paris, Université PSL, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
e-mail: antoine.chomez@obspm.fr
² Univ. Grenoble Alpes, CNRS-INSU, Institut de Planetologie et d’Astrophysique de Grenoble (IPAG), UMR 5274, Grenoble, 38041, France
³ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁴ Institutionen fär astronomi, Stockholms universitet; AlbaNova universitetscentrum, 106 91 Stockholm, Sweden
⁵ Univ. Lyon, Univ. Lyon 1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon (CRAL) UMR5574, 69230 Saint-Genis-Laval, France
⁶ Université Côte d’Azur, OCA, CNRS, Lagrange, 96 Bd de l’Observatoire, 06300 Nice, France
⁷ Pixyl S.A., 5 Av. du Grand Sablon, 38700 La Tronche, France
⁸ ETH Zurich, Institute for Particle Physics and Astrophysics, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
⁹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹⁰ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, 91109, USA
¹¹ Fakultät für Physik, Universität Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
¹² Institüt für Astronomie und Astrophysik, Universität Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
¹³ Physikalisches Institut, Universität Bern, Gesellschaftsstr. 6, 3012 Bern, Switzerland
¹⁴ Department of Astronomy, University of Michigan, 1085 S. University Ave, Ann Arbor, MI 48109, USA
¹⁵ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
¹⁶ Université Grenoble Alpes, CNRS, Observatoire des Sciences de l’Univers de Grenoble (OSUG), 122 Rue de la Piscine, 38400 Saint-Martin-d’Hères, France

Received: 29 May 2023
Accepted: 30 June 2023

Abstract

Context. Since 2019, the direct imaging B-star Exoplanet Abundance STudy (BEAST) at SPHERE@VLT has been scanning the surroundings of young B-type stars in order to ascertain the ultimate frontiers of giant planet formation. Recently, the 17₋₄⁺³ Myr HIP 81208 was found to host a close-in (∼50 au) brown dwarf and a wider (∼230 au) late M star around the central 2.6 M_⊙ primary.

Aims. Alongside the continuation of the survey, we are undertaking a complete reanalysis of archival data aimed at improving detection performances so as to uncover additional low-mass companions.

Methods. We present here a new reduction of the observations of HIP 81208 using the patch covariance algorithm (PACO), a recent and powerful algorithm dedicated to processing high-contrast imaging datasets, as well as more classical algorithms and a dedicated point spread function subtraction approach. The combination of different techniques allowed for a reliable extraction of astrometric and photometric parameters.

Results. A previously undetected source was recovered at a short separation from the C component of the system. Proper motion analysis provided robust evidence for the gravitational bond of the object to HIP 81208 C. Orbiting C at a distance of ∼20 au, this 15 M_Jup brown dwarf becomes the fourth object of the hierarchical HIP 81208 system.

Conclusions. Among the several BEAST stars which are being found to host substellar companions, HIP 81208 stands out as a particularly striking system. As the first stellar binary system with substellar companions around each component ever found by direct imaging, it yields exquisite opportunities for thorough formation and dynamical follow-up studies.