We presented the results of an optical spectroscopic campaign on the HD152248 O+O binary system. Based on a large set of medium and high resolution spectra which provides a very good phase coverage, we derived improved orbital parameters. Combining literature data with our observations, we detected the presence of an apsidal motion with a rate of about 3.4
yr-1. As this system is going to be observed with the XMM X-ray observatory, the new contemporaneous ephemerides we derived are of major importance to correctly interpret the X-ray observation of the HD152248 binary.
We found that the previous classification of both components as supergiants is most probably erroneous and we provide a new classification as O7.5III(f) + O7III(f) for the system. This leads to a better agreement between the observed radii and masses of the components and the typical values for O7-O7.5 giants. The masses we derived are, however, still significantly lower than the ones predicted by the evolutionary tracks.
Finally, we demonstrated that the He II
4686 and H
line profiles result from a blend of two absorption components, associated with the stars of the system, with a broader and more intense emission component. We further showed that their profile and intensity variations are consistent with a wind-wind collision process within the system, assuming that the He II4686 and H
emissions are produced within the interaction region through the recombination process.
The probable existence of a wind-wind interaction within the HD152248 system makes this object an even more attractive target for XMM X-ray observations. The XMM pointings are scheduled to properly cover the orbital cycle and will further allow to investigate the different time scales of the wind interaction process. Detailed comparison of these data with recent theoretical hydrodynamical simulations (e.g. Stevens et al. 1992; Pittard 2000) will provide an important test for these models. It will further help to improve our understanding of the wind-wind collision process, and more widely of the winds of hot stars in general.
Acknowledgements
We wish to thank Dr. O. Stahl and Dr. A. Kaufer for their efficient help in adapting the FEROS reduction package to our data and the referee Dr. Stahl for his suggestions that improve our manuscript. We are grateful to Y. Nazé and Dr. J. Manfroid for their help in the reduction of the BME data. We thank Dr. J.-M. Vreux for many helpful comments and stimulating discussions. We are also grateful to Drs. P. Harmanec and P. Eenens for discussion about HD152248 and for communicating their results prior to publication. We are greatly indebted to the Fonds National de la Recherche Scientifique (Belgium) for multiple support. This research is also supported in part by contract P4/05 ``Pôle d'Attraction Interuniversitaire'' (SSTC-Belgium). Partial support through the PRODEX XMM-OM and INTEGRAL Projects is also gratefully acknowledged. The SIMBAD database was consulted for the bibliography.
Copyright ESO 2001