Study of eclipsing binary and multiple systems in OB associations V: MQ Cen in Crux OB1

The early-type massive binary MQ Cen (\(\mathrm{P}_{\mathit{orb}}=3.7\mbox{ d}\)) has been investigated by means of high-resolution (\(R\sim 48\,000\)) spectral analysis and multi-band (Johnson BVRI and Stromgren \(\mathit{vby}\)) light curve modeling. The physical parameters of the components have been found to be \(M_{1}= 4.26\pm 0.10~\mathrm{M}_{\odot }\), \(R_{1}= 3.72\pm 0.05~\mathrm{R}_{\odot }\), \(T_{\mathrm{eff1}}=16\,600\pm 520\mbox{ K}\), and \(M_{2}= 5.14\pm 0.09~\mathrm{M}_{\odot }\), \(R_{2}= 7.32\pm 0.03~\mathrm{R}_{\odot }\), \(T_{\mathrm{eff2}}=15\,000\pm 500~\mbox{K}\) for the primary and secondary, respectively. The orbital inclination is \(i=87.0\pm 0.2\mbox{ deg}\). The distance to MQ Cen has been derived to be \(d=2460\pm 310\mbox{ pc}\) which locates it in the Crux OB1 association. However, the age of MQ Cen (∼70 Myr) is higher than the one reported for the Crux OB1 association (∼6 Myr). The derived masses are implying a spectral type of B5 for the primary and B4 for the secondary component. Nevertheless, the secondary component, which is more massive, appears to be cooler than the primary component: It has completed its lifetime on the main-sequence and it is now positioned at the turn-off point of the giant branch, meanwhile the less massive primary component is still staying on the main-sequence.