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X-ray observations of the double-binary OB-star system QZ Car (HD 93206)obtained with the Chandra X-ray Observatory over a period of roughly 2 yearsare presented. The orbit of systems A (O9.7 I+b2 v, PA = 21 d) and B (O8 III+o9v, PB = 6 d) are reasonably well sampled by the observations, allowing theorigin of the X-ray emission to be examined in detail. The X-ray spectra can bewell fitted by an attenuated three temperature thermal plasma model,characterised by cool, moderate, and hot plasma components at kT ~ 0.2, 0.7,and 2 keV, respectively, and a circumstellar absorption of ~ 0.2 x 10^22 cm-2.Although the hot plasma component could be indicating the presence of wind-windcollision shocks in the system, the model fluxes calculated from spectral fits,with an average value of ~ 7 x 10^-13 erg s-1 cm-2, do not show a clearcorrelation with the orbits of the two constituent binaries. A semi-analyticalmodel of QZ Car reveals that a stable momentum balance may not be establishedin either system A or B. Yet, despite this, system B is expected to produce anobserved X-ray flux well in excess of the observations. If one considers thewind of the O8 III star to be disrupted by mass transfer the model andobservations are in far better agreement, which lends support to the previoussuggestion of mass-transfer in the O8 III + o9 v binary. We conclude that theX-ray emission from QZ Car can be reasonably well accounted for by acombination of contributions mainly from the single stars and the mutualwind-wind collision between systems A and B.

X-ray emission from the double-binary OB-star system QZ Car (HD 93206)