An imaged 15 MJup companion within a hierarchical quadruple system

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.

Based on data obtained with the ESO/VLT SPHERE instrument under programs 1101.C-0258(A/E).