A study of nine extreme low mass ratio contact binary systems

TL;DR

This study identifies and analyzes nine low mass ratio contact binary systems, providing new physical parameters, exploring their stability, and investigating their evolutionary origins, thus enhancing understanding of these rare stellar configurations.

Contribution

The paper reports the discovery of seven new totally eclipsing low mass ratio binaries and analyzes their stability and progenitors using new observational data and advanced modeling techniques.

Findings

All nine systems have extreme mass ratios from 0.09 to 0.16.

LMR systems tend to have warmer, more massive primaries.

Higher-mass progenitors are more common for low-mass ratio systems.

Abstract

Low mass ratio systems (LMR) are a very interesting class of contact eclipsing binaries challenging the theoretical models of stability. These systems are also considered possible progenitors of the rare low-mass optical transients called red novae. In this study, we present the identification of 7 new totally eclipsing LMR systems from Catalina Sky Surveys (CSS) and 77 LMR candidates from the All Sky Automated Survey (ASAS$-$3). Using the available CSS light curves and new multiband observations for CSS$\_$J210228.3$-$031048 and CSS$\_$J231513.$+$345335 with the 2.3 m Aristarchos telescope at Helmos Observatory, we estimate their physical and absolute parameters and investigate their stability and their progenitors. The light curves are analyzed by performing a 2$-$dimension scan on the mass ratio $-$ inclination plane with Phoebe$-$0.31 scripter while the errors are estimated using Monte-Carlo simulations and heuristic scanning of the parameter space. Our analysis revealed that all 9 CSS systems have extreme mass ratios from 0.09 to 0.16. Our statistical analysis of well$-$studied LMR contact binaries shows that LMR systems tend to have warmer and more massive primaries. The investigation of the progenitors of both low and higher-mass ratio systems reveals a trend for the former to originate from higher-mass ancestors. Finally, we investigate the stability condition by calculating the ratio of spin angular momentum to orbital angular momentum and other stability indicators in the context of the reliability of the solutions.