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UvA-DARE ( Digital Academic Repository ) R 144 revealed as a double-lined spectroscopic binary

R144 is a WN6h star in the 30 Doradus region. It is suspected to be a binary because of its high luminosity and its strong X-ray flux, but no periodicity could be established so far. Here, we present new X-shooter multi-epoch spectroscopy of R144 obtained at the ESO Very Large Telescope. We detect variability in position and/or shape of all the spectral lines. We measure radial velocity variations with an amplitude larger than 250 km s−1 in N IV and N V lines. Furthermore, the N III and N V line Doppler shifts are anticorrelated and the N IV lines show a double-peaked profile on six of our seven epochs. We thus conclude that R144 is a doublelined spectroscopic binary. Possible orbital periods range from two to six months, although a period up to one year is allowed if the orbit is highly eccentric. We estimate the spectral types of the components to be WN5–6h and WN6–7h, respectively. The high luminosity of the system (log Lbol/L ≈ 6.8) suggests a present-day total mass content in the range of about 200–300 M , depending on the evolutionary stage of the components. This makes R144 the most massive binary identified so far, with a total mass content at birth possibly as large as 400 M . We briefly discuss the presence of such a massive object, 60 pc away from the R136 cluster core in the context of star formation and stellar dynamics.