USNO-B1.0 1452-0049820 and ASAS J102556+2049.3: Two W UMa Binaries Close to the Lower Mass-ratio Limit

Photometric observations of the W UMa binaries USNO-B1.0 1452-0049820 and ASAS J102556+2049.3 are presented. The results from the light curve solutions are as follows: (i) the component temperatures are T ₁ = 6400 K and T ₂ = 6300 K for USNO-B1.0 1452-0049820 and T ₁ = 6000 K and T ₂ = 5930 K for ASAS J102556+2049; (ii) the photometric mass ratios are well determined because the targets undergo total eclipses; (iii) both mass ratios are close to the lower mass-ratio limit (0.111 and 0.131 correspondingly); (iv) the fillout factors of the two targets are unexpectedly small (0.045 and 0.243, respectively) for their mass ratios. The global parameters of the target components were estimated on the basis of the empirical relationship “period-total mass” for low mass-ratio binaries. We established a period decrease for ASAS J102556+2049.3 of dP/dt = -3.39 × 10^-6 day yr^-1.