DX Cygni: A triple system with mass transfer

A dozen of new precise times of eclipses were measured for the eclipsing binary DX Cygni as a part of our long-term observational project for studying neglected eclipsing binaries with a short orbital period. Based on a current $O?C$ diagram, we found for the first time that its period is increasing ($dP/P=1.68\times {10}^{?7}$ day/years) and that times of minima show also significant cyclical changes with a period of about 16 years, caused very probably by a third body orbiting the eclipsing pair. The minimal mass of this companion is 0.49 M_⊙. The light curve solution in Phoebe results to the typical Algol-type semidetached configuration where the secondary fills its Roche lobe. The temperature of primary component was fixed to $T_1=5300$ K according to its spectral type, which gives us $T_2=3330\pm 20$ K for the secondary. The photometric mass ratio was estimated $q=0.504\pm 0.012$. We also compare orbital parameters of selected known Algol-type eclipsing binaries with proven mass transfer and a third body.