Abstract
ABSTRACT We present the identification and photometric analysis of 30 new low mass ratio (LMR) totally eclipsing contact binaries found in Catalina Sky Survey data. The LMR candidates are identified using Fourier coefficients and visual inspection. We perform a detailed scan in the parameter plane of mass ratio (q) versus inclination (i) using phoebe -0.31 scripter to derive the best (q, i) pair for the initial models. The relative physical parameters are determined from the final model of each system. A Monte Carlo approach was adopted to derive the parameter errors. The resulting parameters confirm the identification. The approximate absolute physical parameters of the systems are estimated based on the light-curve solutions and Gaia Early Data Release 3 distances. 12 out of 30 new systems have fill-out factors $f\gt 50{{\ \rm per\ cent}}$ and q ≤ 0.25 (deep contact LMR systems), and eight of them, to within errors, are extreme LMR deep systems with q ≤ 0.1. We discuss the evolutionary status of the 30 LMR systems in comparison with the most updated catalogue of LMR systems from the literature. The scenario of the LMR systems as pre-merger candidates forming fast rotating stars is investigated for all systems, new and old, based both on Hut’s stability criteria and critical instability mass ratio (qinst) relation. CSS$\_$J075848.2+125656, with q/qinst = 1.23 ± 0.23, and CSS$\_$J093010.1−021624, with q/qinst = 1.25 ± 0.23, can be considered as merger candidates. $$\begin{eqnarray} \_ \end{eqnarray}$$
Highlights
Eclipsing binary systems of EW light-curve type (EWs) with extreme low mass ratios challenge the current theoretical models since the latter predict coalescence into a single star (Robertson & Eggleton 1977; Eggleton 2010a, and references therein)
We present the identification and photometric analysis of 30 new low mass ratio (LMR) totally eclipsing contact binaries found in Catalina Sky Survey data
We find no trend in which ΔT increases with increasing temperature or with decreasing fill-out factor
Summary
Eclipsing binary systems of EW light-curve type (EWs) with extreme low mass ratios challenge the current theoretical models since the latter predict coalescence into a single star (Robertson & Eggleton 1977; Eggleton 2010a, and references therein). In at least one case, V1309 Sco, such a merger event has been directly observed (Nakano et al 2008) This defined a distinct new class of luminous red novae that was later attributed, upon analysis of archival photometric data from the Optical Gravitational Lensing Experiment (OGLE; Udalski 2003), to the merging components of a cool overcontact eclipsing binary system with a decreasing orbital period (Tylenda et al 2011).
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