2021RAA....21..225P

We present the first photometric analysis of three totally-eclipsing W UMa binaries, NSVS 2443858, NSVS 780649 and V1098 Her. The absolute astrophysical parameters of the stellar components were determined by means of Gaia distances and light curve solutions. The results show that: (i) Two of the systems, NSVS 2443858 and V1098 Her, are of A subtype while the obtained temperature of the secondary component of NSVS 780649 indicates that it is a W-subtype system; (ii) The estimated mass ratios approach the lower limit of the mass ratio assumed by researchers in recent years so our targets could be classified as extreme mass ratio binary (EMRB) systems; (iii) All the systems have deep contact configurations, so they also are deep low mass ratio (DLMR) systems; (iv) The components of our systems are stars of F and G spectral type and undergo total eclipses; (v) The sum 0.871 M☉ of the component masses of NSVS 780649 is below the mass limit of 1.0-1.2 M☉ assumed for the known contact binary stars.