2025AJ....169...85X

We performed photometric and spectroscopic studies of three large amplitude contact binaries: NSVS 2418361, ATLAS J057.1170+31.2384, and NSVS 7377875. The amplitudes of these three systems' light curves are more than 0.7 mag. We analyzed the light curves using the Wilson-Devinney code to yield physical parameters. The photometric solutions suggested that NSVS 7377875 belongs to an A-subtype contact binary, while the others are classified as W-subtype ones. Furthermore, the mass ratio of NSVS 7377875 is higher than 0.72, so it belongs to H-subtype contact binaries. Since their light curves have unequal height at two maxima, which is called the O'Connell effect, a dark spot on the primary component for each target was required to get a better fit of the light curves. The orbital period investigation shows that the period of NSVS 2418361 is increasing, indicating a mass transfer from the the less massive component to the more massive one, while the other targets exhibit no long-term variation. Our spectral subtraction analysis of LAMOST spectra revealed excess emissions in the H_α line, indicating chromospheric activity in all the three targets. The Gaia distance was applied to estimate the absolute parameters of the three targets, and we obtained their evolutionary state. The relationships between the energy transfer parameter of 76 H-subtype contact binaries and their bolometric luminosity ratios, as well as their contact degree, were presented. We discovered that H-subtype systems have less efficient energy transfer rate, which corresponds to the conclusion proposed by Csizmadia & Klagyivik.