Orbital period variations of the eclipsing binaries TU Cnc, VZ Leo, and OS Ori

Variations of the orbital periods of the eclipsing binaries TU Cnc, VZ Leo, and OS Ori are analyzed. Secular period decreases were earlier believed to occur in these systems. It is demonstrated that the period variations of TU Cnc can be represented using the light-time effect corresponding to the orbital motion of the eclipsing binary with a period of 78.6 years around the center ofmass of the triple system, with the mass of the third body being M3 > 0.82M⊙. With the same accuracy, the period variations of VZ Leo and OS Ori can be represented either solely using the light-time effect, or a superposition of a secular period decrease and the light-time effect. For VZ Leo, the period of the long-term orbit is 63.8 years in the former case and 67.9 years in the latter case. Similar masses for the third body are indicated in both cases: M3 > 0.55M⊙ and M3 > 0.61M⊙. For OS Ori, the period of the long-term orbit is 46 years and M3 > 0.5M⊙ in the former case, and the period is 36 years and M3 > 0.6M⊙ in the latter case.