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

TL;DR

This study reports the discovery of a brown dwarf and a low-mass star orbiting a young B star, revealing a potentially Kozai-resonant system with unusual orbital configuration, using high-contrast imaging techniques.

Contribution

First detection of a brown dwarf and a low-mass star around a young B star using VLT/SPHERE, highlighting a dynamically intriguing system with near-orthogonal orbits.

Findings

Brown dwarf companion with ~67 M_J detected

Low-mass stellar companion with ~0.135 M_sun detected

System likely in Kozai resonance with orthogonal orbital planes

Abstract

Recent observations from B-star Exoplanet Abundance Study (BEAST) have illustrated the existence of sub-stellar companions around very massive stars. In this paper, we present the detection of two lower mass companions to a relatively nearby ($148.7^{+1.5}_{-1.3}$ pc), young ($17^{+3}_{-4}$ Myr), bright (V=$6.632\pm0.006$ mag), $2.58\pm0.06~ M_{\odot}$ 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. Analysis of the photometry obtained gives mass estimates of $67^{+6}_{-7}~M_J$ for the inner companion and $0.135^{+0.010}_{-0.013}~M_{\odot}$ for the outer companion, indicating the former to be most likely a brown dwarf and the latter to be 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 derived 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.