The study of 11 contact binaries with mass ratios less than 0.1

Multi-band photometric observations of 11 totally eclipsing contact binaries were carried out. Applying the Wilson-Devinney program, photometric solutions were obtained. There are two W-subtype systems, which are CRTS J133031.1+161202 and CRTS J154254.0+324652, and the rest of the systems are A-subtype systems. CRTS J154254.0 + 324652 has the highest fill-out factor with 94.3 per cent, and the lowest object is CRTS J155009.2 + 493639 with only 18.9 per cent. The mass ratios of the 11 systems are all less than 0.1, which means that they are extremely low-mass ratio binary systems. We performed period variation investigation and found that the orbital periods of three systems decrease slowly, which may be caused by the angular momentum loss, and those of six systems increase slowly, which indicates that the materials may transfer from the secondary component to the primary component. LAMOST low-resolution spectra of four objects were analysed, and using the spectral subtraction technique, H alpha emission line was detected, which means that the four objects exhibit chromospheric activity. In order to understand their evolutionary status, the mass-luminosity and mass-radius diagrams were plotted. The two diagrams indicate that the primary component is in the main sequence evolution stage, and the secondary component is above TAMS, indicating that they are over-luminous. To determine whether the 11 systems are in a stable state, the ratio of spin angular momentum to orbital angular momentum (J(s)/J(o)) and the instability parameters were calculated, and we argued that CRTS J234634.7 + 222824 is on the verge of a merger.

Automated summary

Multi-band photometric observations of 11 totally eclipsing contact binaries were conducted, and photometric solutions were obtained using the Wilson-Devinney program. Among them, two systems are of W subtype, namely CRTS J133031.1+161202 and CRTS J154254.0+324652, while the others are of A subtype. The mass ratios of all 11 systems are less than 0.1, indicating extremely low-mass ratio binary systems. The study revealed period variations in the systems, with three systems showing slow decrease in orbital periods possibly due to angular momentum loss, and six systems showing slow increase in orbital periods indicating material transfer from secondary to primary component. Analysis of LAMOST low-resolution spectra detected H alpha emission line in four objects, suggesting chromospheric activity. Mass-luminosity and mass-radius diagrams were plotted to understand their evolutionary status, showing the primary component in main sequence evolution stage and the secondary component above TAMS, indicating over-luminosity. The stability of the 11 systems were evaluated using the ratio of spin angular momentum to orbital angular momentum and instability parameters, suggesting CRTS J234634.7 + 222824 is on the verge of a merger.