INVESTIGATION ON FOUR CONTACT BINARY SYSTEMS AND A SEMI-DETACHED ONE AT THE BEGINNING OF THE CONTACT PHASE

We present B, V, R-c and I-c light curves of four contact binary systems and one semi-detached system. New observations confirm and revise the short -period (0.22-0.25d) of the systems and that all stars belong to the spectral type K. In J105924 and J164349 a third light was found while the shape of the light curves of four systems (excluding J105924) suggests the presence of inhomogeneities on the surface of one component which confirms that the systems are active. Also they are observed at low orbital inclination i E (41(o) , 62(o)). The temperature difference range is triangle T E (4, 640)K and the mass ratios q E (0.20, 0.75). Absolute parameters are estimated using statistical diagrams. The systems follow the general pattern of the relative subtype of W Ursae Majoris systems. The sum of the component masses of four systems is below the mass limit of 1.0- 1.2M(circle dot) assumed for the known contact binary stars; this tells us that they belong to the class of low mass contact binaries.