2024MNRAS.527.6406L

The photometric and spectroscopic studies of three contact binaries, ASASSN-V J052036.28+144711.0, ASASSN-V J064846.22+241709.9, and ASASSN-V J073441.02+555833.0 were performed for the first time. The periods of all the three targets are longer than 0.5 d, and we discovered that their mass ratios are all smaller than 0.25. So, they are long-period low mass-ratio contact binaries. ASASSN-V J052036.28+144711.0 and ASASSN-V J064846.22+241709.9 are medium contact binaries. ASASSN-V J073441.02+555833.0 is a deep contact binary, which is also the only one existing O'Connell effect. We attached a dark spot on its secondary component for a better fit of light curves featuring asymmetry. From orbital period analysis, two of the three targets are believed to demonstrate a secular period increase, while one shows no long-term variation. We employed the spectral subtraction approach to investigate the LAMOST spectra, while all of the three binaries show no H α emission line, implying no chromospheric activity. Their initial masses, current average densities, and mass transfer rates between the two components were calculated. We obtained that the three targets are stable for the moment.