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tokens: We are grateful to the anonymous reviewer for constructive comments that helped to improve the manuscript. This work has extensively used NASA Astrophysics Data System, and the SIMBAD database, operated at CDS, Strasbourg, France. This publication made use of data products provided by the NASA/IPAC Infrared Science Archive. We are grateful to Dr. J Maíz Apellániz for kindly providing us with the optical spectrum of Cyg OB2 12 and to Dr. M Mapelli for a useful discussion on the dynamics of multiple systems. L.M.O. acknowledges support by DLR grant 50 OR 1302. A.S. is supported by the Deutsche Forschungsgemeinschaft (DFG) under grant HA 1455/26. D.P.H. was supported by NASA grant GO5-16009A. Facility: CXO (HETG/ACIS) .