Rubio Diez, M. M., Najarro, F., García, M., Sundqvist, J. O. 2017. Re-examing the Upper Mass Limit of Very Massive Stars: VFTS 682, an isolated similar to 130 M-circle dot twin of R136’s WN5h core stars. Lives and Death Thrones of Massive Starts, IAU Symposium Proceedings Series, 329th Symposium of the International-Astronomical-Union (IAU), 12, 329, 131-135, DOI: 10.1017/S1743921317002447
Recent studies of WNh stars at the cores of young massive clusters have challenged the previously accepted upper stellar mass limit (similar to 150 M-circle dot), suggesting some of these objects may have initial masses as high as 300 M-circle dot. We investigated the possible existence of observed stars above similar to 150 M-circle dot by i) examining the nature and stellar properties of VFTS 682, a recently identified WNh5 very massive star, and ii) studying the uncertainties in the luminosity estimates of R136’s core stars due to crowding. Our spectroscopic analysis reveals that the most massive members of R136 and VFTS 682 are very similar and our K-band photometric study of R136′ s core stars shows that the measurements seem to display higher uncertainties than previous studies suggested; moreover, for the most massive stars in the cluster, R136a1 and a2, we found previous magnitudes were underestimated by at least 0.4 mag. As such, luminosities and masses of these stars have to be significantly scaled down, which then also lowers the hitherto observed upper mass limit of stars.