中国科学院云南天文台机构知识库

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, f(1), are q(ph) = 0.255(+/- 0.002) and f(1) = 81.2(+/- 0.2)% for AV Hya, and q(ph) = 0.093(+/- 0.003) and f(1) = 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 P-3 = 37.2(+/- 0.7) yr and A = 0.(d)0095(+/- 0.(d)0006) for AV Hya, and P-3 = 62.5(+/- 1.0) yr andA = 0.(d)0183(+/- 0.(d)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) x 10(-7) days yr(-1) for AV Hya and dP/dt = -0.92(+/- 0.04) x 10(-7) days yr(-1) 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.