The orbital period analyses for two cataclysmic variables: UZ Fornacis and V348 Puppis inside Period Gap

TL;DR

This study analyzes orbital period changes in two cataclysmic variables inside the period gap, revealing period increases, possible cyclical variations, and potential tertiary companions, challenging simple mass transfer explanations.

Contribution

It provides new eclipse timings and detailed O-C analyses, identifying cyclical period variations and suggesting possible tertiary components in UZ Fornacis.

Findings

Orbital periods are increasing in both CVs.

UZ Fornacis shows a ~23.4-year cyclical period change.

Potential brown dwarf tertiary in UZ Fornacis.

Abstract

Four newest CCD eclipse timings of the white dwarf for polar UZ Fornacis and Six updated CCD mid-eclipse times for SW Sex type nova-like V348 Puppis are obtained. The detailed O-C analyses for both CVs inside period gap are made. Orbital period increases at a rate of $2.63(\pm0.58)\times10^{-11} s\;s^{-1}$ for UZ Fornacis and of $5.8(\pm1.9)\times10^{-12} s\;s^{-1}$ for V348 Puppis, respectively, are discovered in their new O-C diagrams. However, the conservative mass transfer from the secondary to the massive white dwarf cannot explain the observed orbital period increases for both CVs, which are regarded as part of modulations at longer periods. Moreover, the O-C diagram of UZ Fornacis shows a possible cyclical change with a period of $\sim23.4(\pm5.1)yr$. For explaining the observed cyclical period changes in UZ Fornacis, both mechanisms of magnetic activity cycles in the late-type secondary and the light travel-time effect are regarded as two probable causes. Not only does the modulation period 23.4yr obey the empirical correlation derived by \cite{lan99}, but also the estimated fractional period change $\Delta P/P\sim7.3\times10^{-7}$ displays a behavior similar to that of the CVs below the period gap. On the other hand, a calculation for the light travel-time effect implies that the tertiary component in UZ Fornacis may be a brown dwarf with a high confidence level, when the orbital inclination of the third body is larger than $16^{\circ}$.