We present new Strömgren photometry and medium-dispersion spectroscopy of the early-type eclipsing binary AI Cru. The masses and radii of the two components are found to be (9.8±0.5) and (5.8±0.3) solar masses and (4.9±0.1) and (4.4±0.1) solar radii, respectively. We confirm the semi-detached nature of the system noted by Russo and show by comparison with stationary models by Horn, Kriz & Plavec that AI Cru has probably passed through the rapid phase of Case A mass transfer. We suggest that the original system may have had a period of about 1.3 day and that the roles of the current primary and secondary components were at that time reversed.
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Bell et al. (1987) studied this question.