A Study of the Orbital Periods of Deeply Eclipsing SW Sextantis Stars

TL;DR

This study analyzes five decades of eclipse data for 18 SW Sextantis stars, revealing some exhibit cyclical orbital period variations and others show secular period reductions, providing updated ephemerides for future observations.

Contribution

It offers the first long-term analysis of orbital period variations in SW Sextantis stars, identifying cyclical and secular changes and providing new ephemerides.

Findings

Some stars show cyclical period variations with 10-40 year cycles.

Two stars exhibit secular period reductions.

New ephemerides are provided for all studied stars.

Abstract

Results are presented of a five-year project to study the orbital periods of eighteen deeply eclipsing novalike cataclysmic variables, collectively known as SW Sextantis stars, by combining new measurements of eclipse times with published measurements stretching back in some cases over fifty years. While the behaviour of many of these binary systems is consistent with a constant orbital period, it is evident that in several cases this is not true. Although the time span of these observations is relatively short, evidence is emerging that the orbital periods of some of these stars show cyclical variation with periods in the range 10-40 years. The two stars with the longest orbital periods, V363 Aur and BT Mon, also show secular period reduction with rates of -6.6 \times 10^{-8} days/year and -3.3 \times 10^{-8} days/year. New ephemerides are provided for all eighteen stars to facilitate observation of future eclipses.