Low-mass stellar and substellar candidate companions around massive stars in Sco OB1 and M17

TL;DR

This study investigates the presence and characteristics of very low-mass and substellar companions around massive stars in Sco OB1 and M17, using high-contrast imaging to explore a poorly understood mass ratio regime.

Contribution

First direct imaging survey of low-mass and substellar companions around massive stars in Sco OB1 and M17, providing candidate identifications and initial proper motion analysis.

Findings

Two brown dwarf candidates identified.

Four low-mass stellar companions identified.

Proper motion analysis inconclusive without follow-up.

Abstract

Massive stars are recognized for their high degree of multiplicity, yet the mass ratio regime below 0.1 remains insufficiently explored. It is therefore unknown whether extremely low-mass (possibly substellar) companions can form and survive in the direct UV-irradiated environment of massive stars. In this paper, we discuss VLT/SPHERE IFS (0".15 - 0".85) observations of six massive O- and early B-type stars in Sco OB1 and M17 that each have a low-mass candidate companion. Two targets have companions that are brown dwarf candidates. The other four have candidate companions in the low end of the stellar mass regime ($\leq$ 0.30 M$_\odot$). For three of these, we have obtained a second epoch observation. At least two sources exhibit similar proper motion to that of their central star. However, given the expected proper motion of background objects, this does not imply certain companionship. We show how future follow-up observations of the brown dwarf candidate companions in $J$, $H$ and $L$ bands should allow for an unambiguous confirmation of their nature.