LAUSR

Abstract Photometric observations of the W UMa binaries PY Boo and NSVS 7328383 with periods of around 0.27 d are presented. The light curve solutions reveal that the components of both targets are stars of K type (temperatures T1=4770 K, T2=5080 K and T1=5146 K, T2=5056 K, respectively,) and undergo total eclipses (both orbital inclinations are  ∼ 78°). The well-determined mass ratios of 0.20 and 0.22 put PY Boo and NSVS 7328383 in the list of binaries with the smallest mass ratio whose number is less than 50. Both target configurations have fillout factor 0.17. The light curve distortions were reproduced by cool spots on the side of their primaries with angular size of 15°. Our observations confirmed the period decrease of PY Boo and we estimated its rate as –7.186  ×  10 − 7 d yr − 1 . The period of NSVS 7328383 was improved and the new value is smaller than the previous one by 0.19 s. The target global parameters were estimated by the empirical relation “period – total mass” of low mass-ratio binaries. The calculated distance d = 228 ± 21 pc of PY Boo is within the errors of the value determined by GAIA(DR2) of 209 ± 20 pc. PY Boo and NSVS 7328383 turned out similar W UMa binaries in period, orbital inclination, magnitude, temperature of the components, mass ratio, fillout factor, and even in size and location of the spots.