1994A&A...291..185L

New spectroscopic and photometric results for the eclipsing binary AB Cru are presented. The first photoelectric UBV light curves of this O8-type system were solved with a newly developed light curve modelling code taking into account radiation pressure effects due to the mutual irradiation of the binary components. The radiative forces exerted on the irradiated surface layers reach a few percent of the gravitational attraction of the companion, and have non-negligible influence on the binary structure. The first radial velocity curve of AB Cru, based on high resolution Coude-Echelle spectra, allowed for an accurate determination of the spectroscopic mass ratio and the radial velocity amplitudes. For the first time, precise absolute dimensions of AB Cru can be given: the stellar masses for the primary and secondary component are 19.75 and 6.95M_☉, the radii 10.54 and 8.85R_☉, and the luminosities 1.64x10⁵ and 3.84x10⁴M_☉. A semi-detached system configuration was found. The evolutionary state of AB Cru is discussed; both stellar components are slightly evolved, but still located within the upper main sequence band. Strong indications for case A mass transfer from the secondary towards the primary are found, suggesting that AB Cru has formerly undergone a reversal of its mass ratio.