We present the photometric results of the eclipsing cataclysmic variable (CV) WZ Sge near the period minimum ($P_{min}$). Eight new mid-eclipse times were determined and the orbital ephemeris was updated. Our result shows that the orbital period of WZ Sge is decreasing at a rate of $dot{P}=-2.72(pm0.23)times{10^{-13}},s s^{-1}$. This secular decrease, coupled with previous detection of its donor, suggest that WZ Sge is a pre-bounce system. Further analysis indicates that the observed period decrease rate is about $1.53$ times higher than pure gravitational radiation (GR) driving. We constructed the evolutionary track of WZ Sge, which predicts that $P_{min}$ of WZ Sge is $sim77.98 (pm0.90)$ min. If the orbital period decreases at the current rate, WZ Sge will evolve past its $P_{min}$ after $sim25.3$ Myr. Based on the period evolution equation we find $dot{M}_{2}simeq4.04(pm0.10)times10^{-11}M_{odot}yr^{-1}$, which is compatible with the current concept of CV evolution at ultrashort orbital periods.
تحميل البحث