Context : Light curves of the long-period Algols are known for their complex shape ( asymmetry in the eclipse , light variations outside eclipse , changes from cycle-to-cycle ) , and their interpretation is not possible in the standard model of binary stars .

Aims : Complex structures present in these active Algol systems could be studied with the eclipse-mapping method which was successfully applied to the new 7-color photometric observations in the Geneva system of W Cru , belonging to the isolated group of these active Algols .

Methods : Several cycles of this long-period ( 198.5 days ) eclipsing binary have been covered by observations .
We have used a modified Rutten ’ s approach to the eclipse-mapping .
The optimization of the system ’ s parameters and the recovery of the disk intensity distrubution are performed using a genetic algorithm ( GA ) .

Results : It is found that a primary ( hot ) component is hidden in the thick accretion disk which confirms previous findings .
The mass of the primary component , M _ { 1 } = 8.2 M _ { \odot } indicates that it is a mid-B type star .
The mass-losing component is filling its critical lobe which , for the system ’ s parameters , means it is a G-type supergiant with a mass M _ { 2 } = 1.6 M _ { \odot } .
The disk is geometrically very extended and its outer radius is about 80 % of the primary ’ s critical lobe .
A reconstructed image reveals a rather clumpy and nonuniform brightness distribution of an accretion disk rim in this almost edge-on seen system .
This clumpiness accounts for light curve distortions and asymmetries , as well as for secular changes .

Conclusions :