Constraining the Fundamental Parameters of the O‐Type Binary CPD −41 7733

Using a set of high-resolution spectra, we studied the physical and orbitalproperties of the O-type binary CPD-41 7733, located in the core of \ngc. Wereport the unambiguous detection of the secondary spectral signature and wederive the first SB2 orbital solution of the system. The period is 5.6815 +/-0.0015 d and the orbit has no significant eccentricity. CPD-41 7733 probablyconsists of stars of spectral types O8.5 and B3. As for other objects in thecluster, we observe discrepant luminosity classifications while usingspectroscopic or brightness criteria. Still, the present analysis suggests thatboth components display physical parameters close to those of typical O8.5 andB3 dwarfs. We also analyze the X-ray light curves and spectra obtained duringsix 30 ks XMM-Newton pointings spread over the 5.7 d period. We find nosignificant variability between the different pointings, nor within theindividual observations. The CPD-41 7733 X-ray spectrum is well reproduced by athree-temperature thermal mekal model with temperatures of 0.3, 0.8 and 2.4keV. No X-ray overluminosity, resulting e.g. from a possible wind interaction,is observed. The emission of CPD-41 7733 is thus very representative of typicalO-type star X-ray emission.Comment: Accepted by ApJ, 15 pages, 9 figure