Constraining the fundamental parameters of the O-type binary

H. Sana^{1,2}, G. Rauw^{1} and E. Gosset^{1}

1. Liege University, Belgium
2. European Southern Observatory, Chile

Using a set of high-resolution spectra, we studied the physical and orbital
properties of the O-type binary CPD-41 7733, located in the core of ngc. We
report the unambiguous detection of the secondary spectral signature and we
derive 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 probably
consists of stars of spectral types O8.5 and B3. As for other objects in the
cluster, we observe discrepant luminosity classifications while using
spectroscopic or brightness criteria. Still, the present analysis suggests that
both components display physical parameters close to those of typical O8.5 and
B3 dwarfs. We also analyze the X-ray light curves and spectra obtained during
six 30~ks XMM-Newton pointings spread over the 5.7 d period. We find no
significant variability between the different pointings, nor within the
individual observations. The CPD-41 7733 X-ray spectrum is well reproduced by a
three-temperature thermal mekal model with temperatures of 0.3, 0.8 and
2.4~keV. 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 typical O-type star X-ray emission.

Reference: Accepted by ApJ
Status: Manuscript has been accepted