HD 93206 = QZ Carinae UBVRI photometry

Using archival and new spectra, and a rich collection of ground-based and space photometric observations, we carried out a detailed study of this object. We provide a much improved description of both short orbits and a good estimate of the mutual period of both binaries of about 14500d (i.e. 40 years).

For the first time, we detected weak lines of the fainter component of the 6.0d eclipsing binary in the optical region of the spectrum, measured their radial velocities, and derived a mass ratio of M_Ac2_/M_Ac1_=1.29, which is the opposite of what was estimated from the International Ultraviolet explorer (IUE) spectra. We confirm that the eclipsing subsystem Ac is semi-detached and is therefore in a phase of large-scale mass transfer between its components.