Insights into the evolution of low mass-ratio contact binaries: orbital period analysis of 37 systems

ABSTRACT This study presents a comprehensive investigation of orbital period (OP) variations in 37 low-mass ratio contact binaries (LMRCBs) ($q < 0.25$). New minima times (MTs) were calculated from TESS and SuperWASP observations (a total of 452 minima for 37 systems), supplemented by values collected from the literature. For each target, Observed (O)$-$Calculated (C) diagrams were constructed to examine both long-term (secular) trends and short-term cyclic variations. Our findings reveal that most systems exhibit significant long-term period evolution, while some display periodic modulations that can be interpreted as the light-time effect (LITE) caused by a tertiary companion, or alternatively, these modulations may result from magnetic activity. In the constructed $q-$dP/dt diagram, it was observed that the rate of decrease in OP varied over a wider range than the rate of increase in OP. Additionally, Hertzsprung–Russell (HR), logM$_{tot}$$-$logJ, and q$-$J$_{s}$/J$_{o}$ diagrams were generated to explore the evolutionary states of the candidate systems. These results provide compelling evidence that LMRCBs may represent dynamically unstable configurations, offering crucial insights into the late evolutionary stages of close binary systems.