Space astrometry of the very massive ∼150 M⊙ candidate runaway star VFTS682

Abstract

ABSTRACT How very massive stars form is still an open question in astrophysics. VFTS682 is among the most massive stars known, with an inferred initial mass of ≳$150\,\text{M}_\odot$. It is located in 30 Doradus at a projected distance of 29 pc from the central cluster R136. Its apparent isolation led to two hypotheses: either it formed in relative isolation or it was ejected dynamically from the cluster. We investigate the kinematics of VFTS682 as obtained by Gaia and Hubble Space Telescope astrometry. We derive a projected velocity relative to the cluster of $38\pm 17{\, \mathrm{km\ s^{-1}}}$ (1σ confidence interval). Although the error bars are substantial, two independent measures suggest that VFTS682 is a runaway ejected from the central cluster. This hypothesis is further supported by a variety of circumstantial clues. The central cluster is known to harbour other stars more massive than $150\, \text{M}_\odot$ of similar spectral type and recent astrometric studies on VFTS16 and VFTS72 provide direct evidence that the cluster can eject some of its most massive members, in agreement with theoretical predictions. If future data confirm the runaway nature, this would make VFTS682 the most massive runaway star known to date.