Rauw, G.G.RauwNazé, Y.Y.NazéWright, N. J.N. J.WrightDrake, J. J.J. J.DrakeGUARCELLO, Mario GiuseppeMario GiuseppeGUARCELLOPrinja, R. K.R. K.PrinjaPeck, L. W.L. W.PeckAlbacete Colombo, J. F.J. F.Albacete ColomboHerrero, A.A.HerreroKobulnicky, H. A.H. A.KobulnickySCIORTINO, SalvatoreSalvatoreSCIORTINOVink, J. S.J. S.Vink2020-03-032020-03-0320150067-0049http://hdl.handle.net/20.500.12386/23087The Liège team acknowledges support from Belspo through an XMM PRODEX contract, from the FRS/FNRS and from an ARC grant for Concerted Research Actions, financed by the Federation Wallonia-Brussels. N.J.W. was supported by a Royal Astronomical Society research fellowship. Facilities: CXO , XMM .We report on the analysis of the Chandra-ACIS data of O, B, and WR stars in the young association Cyg OB2. X-ray spectra of 49 O-stars, 54 B-stars, and 3 WR-stars are analyzed and for the brighter sources, the epoch dependence of the X-ray fluxes is investigated. The O-stars in Cyg OB2 follow a well-defined scaling relation between their X-ray and bolometric luminosities: {log}\\frac{{L}<SUB>{{X</SUB>}}}{{L}<SUB>{bol</SUB>}}=-7.2+/- 0.2. This relation is in excellent agreement with the one previously derived for the Carina OB1 association. Except for the brightest O-star binaries, there is no general X-ray overluminosity due to colliding winds in O-star binaries. Roughly half of the known B-stars in the surveyed field are detected, but they fail to display a clear relationship between L<SUB>X</SUB> and L<SUB>bol</SUB>. Out of the three WR stars in Cyg OB2, probably only WR 144 is itself responsible for the observed level of X-ray emission, at a very low {log}\\frac{{L}<SUB>{{X</SUB>}}}{{L}<SUB>{bol</SUB>}}=-8.8+/- 0.2. The X-ray emission of the other two WR-stars (WR 145 and 146) is most probably due to their O-type companion along with a moderate contribution from a wind-wind interaction zone.STAMPAenArticle10.1088/0067-0049/221/1/12-s2.0-84948747946000366620600001https://iopscience.iop.org/article/10.1088/0067-0049/221/1/1https://arxiv.org/pdf/1401.80982015ApJS..221....1RFIS/05 - ASTRONOMIA E ASTROFISICAScienze Fisiche Settori ERC (ERC) di riferimento::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation