New low mass ratio contact binaries in the Catalina Sky Survey

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>50 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 (q_(inst)) relation. CSS__J075848.2+125656, with q/q_(inst) = 1.23 ± 0.23, and CSS__J093010.1−021624, with q/q_(inst) = 1.25 ± 0.23, can be considered as merger candidates.