BEAST detection of a brown dwarf and a low-mass stellar companion around the young bright B star HIP 81208^★

¹ Institutionen för astronomi, Stockholms universitet, AlbaNova universitetscentrum, Roslagstullsbacken 21, 106 91 Stockholm, Sweden
e-mail: gayathri.viswanath@astro.su.se
² INAF - Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
³ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, 92195 Meudon, France
⁴ Cornell Center for Astrophysics and Planetary Science, Department of Astronomy, Cornell University, 404 Space Sciences Building, Ithaca, NY 14853, USA
⁵ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena CA 91109, USA
⁶ Department of Physics and Astronomy, University of Rochester, 500 Wilson Blvd, Rochester, NY 14627, USA
⁷ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
⁸ Laboratoire J.-L. Lagrange, Université Cote d’Azur, CNRS, Observatoire de la Cote d’Azur, Boulevard de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
⁹ University of Grenoble Alpes, IPAG, CS 40700, 38058 Grenoble Cedex 9, France
¹⁰ Aix Marseille Université, CNRS, LAM, Pôle de l’Étoile Site de Château-Gombert, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
¹¹ ETH Zurich, Rämistrasse 101, 8092 Zurich, Switzerland
¹² Max Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹³ Observatoire de Geneve, University of Geneva, Ch. de Pegasi 51, 1290 Versoix, Switzerland
¹⁴ CRAL, UMR 5574, CNRS, Université Lyon 1, 9 avenue Charles André, 69561 Saint-Genis-Laval Cedex, France
¹⁵ Department of Astronomy, University of Michigan, 1085 S. University Ave, Ann Arbor, MI 48109, USA

Received: 15 February 2023
Accepted: 7 May 2023

Abstract

Recent observations by the B-star Exoplanet Abundance Study (BEAST) illustrate the existence of substellar companions around very massive stars. Here, we present the detection of two lower mass companions to a relatively nearby (148.7_−1.3^+1.5 pc), young (17₋₄⁺³ Myr), bright (V = 6.632 ± 0.006 mag), 2.58 ± 0.06 M_⊙ B9V star HIP 81208 residing in the Sco-Cen association using the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument at the Very Large Telescope (VLT) in Chile. Our analysis of the photometry obtained gives mass estimates of 67₋₇⁺⁶ M_J for the inner companion and 0.135_−0.013^+0.010 M_⊙ for the outer companion, indicating that the former is most likely a brown dwarf and the latter a low-mass star. The system is compact but unusual, as the orbital planes of the two companions are likely close to orthogonal. The preliminary orbital solutions we derive for the system indicate that the star and the two companions are likely in a Kozai resonance, rendering the system dynamically very interesting for future studies.