2012AJ....144...50Y

We present BVR photometric observations and several eclipsing times for AV Hya and DZ Cas from 2004 to 2011. Using the Wilson-Devinney method, the photometric solutions with hot spots were deduced from their asymmetric light curves. The results indicate that both stars are Algol-type binaries, whose mass ratio, q_ph, and fill-out factor of the primary, f₁, are q_ph= 0.255(± 0.002) and f₁= 81.2(± 0.2)% for AV Hya, and q_ph= 0.093(± 0.003) and f₁= 98.7(± 0.3)% for DZ Cas. Based on all available light minimum times, it is discovered that the O - C curve of each star could be described by a light-time orbit overlying on a downward parabola. Their periods and amplitudes are P₃= 37.2(± 0.7) yr and A = 0.<SUP>d</SUP>0095(±0.<SUP>d</SUP>0006) for AV Hya, and P₃= 62.5(± 1.0) yr and A = 0.<SUP>d</SUP>0183(±0.<SUP>d</SUP>0007) for DZ Cas. Cyclic variations may result from the light-time effect due to the third body. The secular period decrease rates are dP/dt = -1.47(± 0.04) x10^–7 days./yr for AV Hya and dP/dt = -0.92(± 0.04)x10^–7 days./yr for DZ Cas. This may be interpreted using mass and angular momentum loss from the system. With decreasing period, the fill-out factor of the primary increases and it may finally fill its inner Roche lobe. Therefore, AV Hya and DZ Cas with a secular period decrease will evolve from semi-detached configurations into contact ones.