Possible companions in low-mass eclipsing binaries: V380 Dra, BX Tri, and V642 Vir

We present the new results of our long-term observational project to analyze the orbital period variations of low-mass eclipsing binaries. More then 200 new precise mid-eclipse times recorded with a CCD were obtained for three eclipsing binaries with short orbital periods: V380 Dra (P = 0.49^d), BX Tri (0.19^d), and V642 Vir (0.52^d). Observed-minus-calculated diagrams of the stars were analyzed using all reliable timings, and new parameters of the light-time effect were obtained. We derived for the first time the short orbital periods of possible third bodies of 10--20 years for these objects. We calculated that the minimum masses of the third component are close to 0.2 M_⊙, which corresponds to the mass of M4 -- M5 red dwarfs. The multiplicity of these systems also plays an important role in the precise determination of their physical parameters.