Abstract
Photometric observations in Sloan g' and i' bands of four eclipsing W UMa binaries are presented. They allowed the improvement of system ephemerides. The light curve solutions led to the following results: (i) CSS J071813.2+505000 is barely an overcontact system, NSVS 2459652 and NSVS 7377875 are overcontact binaries with an intermediate fillout factor, while NSVS 7178717 has a deep-contact configuration; (ii) NSVS 7178717 undergoes total eclipses while the other three targets exhibit partial eclipses; (iii) The components of each target are almost the same in temperature: those of CSS J071813.2+505000 are early G stars while those of the other three targets are of K spectral type; (iv) The targets with late components reveal spot activity; (v) NSVS 2459652 and NSVS 7377875 are W UMa binaries of H subtype; (vi) The relation mass ratio - luminosity ratio of our targets confirms the results from previous statistical analysis of W UMa systems.
