2006MNRAS.371...67S

We present the results of an optical spectroscopic campaign on the massive binary HD152219 located near the core of the NGC6231 cluster. Though the primary to secondary optical brightness ratio is probably about 10, we clearly detect the secondary spectral signature and we derive the first reliable SB2 orbital solution for the system. The orbital period is close to 4.2403d and the orbit is slightly eccentric (e = 0.08±0.01). The system is most probably formed by an O9.5 giant and a B1-2 V-III star. We derive minimal masses of 18.6±0.3 and 7.3±0.1M_☉for the primary and secondary, respectively, and we constrain the stellar radius at values about 11 and 5R_☉. INTEGRAL-Optical Monitoring Camera (OMC) data reveal that HD152219 is the third O-type eclipsing binary known in NGC6231. In the Hertzsprung-Russell (HR) diagram, the primary component lies on the blue edge of the β Cep-type instability strip and its spectral lines display clear profile variations that are reminiscent of those expected from non-radial pulsations. Finally, we report the analysis of XMM-Newton observations of the system. The X-ray spectrum is relatively soft and is well reproduced by a two-temperature mekal model with kT₁ = 0.26keV and kT₂= 0.67keV. The X-ray flux is most probably variable on a time-scale of days. The average X-ray luminosity during our campaign is log(L_X) ~ 31.8 (erg/s), but shows fluctuations of about 10 per cent around this value.