2014A&A...568L..13W

Very massive stars (M>100M_☉) are very rare objects, but have a strong influence on their environment. The formation of this kind of objects is of prime importance in star formation, but observationally still poorly constrained. We report on the identification of a very massive star in the central cluster of the star-forming region W49. We investigate near-infrared K-band spectroscopic observations of W49 from VLT/ISAAC together with JHK images obtained with NTT/SOFI and LBT/LUCI. We derive the spectral type of W49nr1, the brightest star in the dense core of the central cluster of W49. On the basis of its K-band spectrum, W49nr1 is classified as an O2-3.5If* star with a K-band absolute magnitude of -6.27±0.10mag. The effective temperature and bolometric correction are estimated from stars of similar spectral type. After comparison to the Geneva evolutionary models, we find an initial mass between 100M_☉ and 180M_☉. Varying the extinction law results in a larger initial mass range of 90-250M_☉.