Orbital period behaviour of three semi-detached binaries AI Cru, V1898 Cyg and Z Vul

In this research, orbital period variation of three semi-deteached binaries AI Cru, V1898 Cyg and Z Vul investigated using all published eclipse times. O-C analysis method has preferred as the method and the orbital periods of all systems are determined to increase. The changing rate of their period has been determined to be 0.8, 4.1 and 0.8 s/century for AI Cru, V1898 Cyg and Z Vul, respectively. Mass transfer between components has proposed as the cause of orbital period increase. For AI Cru, V1898 Cyg and Z Vul, mass transfer from less massive component to more massive and mass transfer rate was found to be 2.9×10-7, 1.5×10-7 and 5.3×10-8 M⊙/year respectively. Cyclic change has also seen in AI Cru and V1898 Cyg with increasing parabolic change. Cyclic periodic changes can be explained as being the result of a light-travel time effect via a tertiary body around the eclipsing pair. The minimum mass of probable tertiary components around AI Cru and V1898 Cyg were found to be 0.38 M⊙ and 0.26 M⊙, respectively.