# WZ Sge: an eclipsing cataclysmic variable evolving towards the period minimum

## TL;DR

This study analyzes the eclipsing cataclysmic variable WZ Sge near its period minimum, updating its orbital parameters, and predicting its future evolution and mass transfer rate based on observed period decrease.

## Contribution

The paper provides new mid-eclipse timings, refines the orbital ephemeris, and models the evolutionary track of WZ Sge, demonstrating its status as a pre-bounce system and predicting its future period evolution.

## Key findings

- WZ Sge's orbital period is decreasing at a rate of approximately -2.72×10^{-13} s s^{-1}.
- The predicted period minimum for WZ Sge is about 78 minutes.
- WZ Sge will pass its period minimum in roughly 25.3 million years.

## Abstract

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.