We used the newly commissioned 50 cm Binocular Network ( 50BiN ) telescope at Qinghai Station of Purple Mountain Observatory ( Chinese Academy of Sciences ) to observe the old open cluster NGC 188 in V and R as part of a search for variable objects .
Our time-series data span a total of 36 days .
Radial-velocity and proper-motion selection resulted in a sample of 532 genuine cluster members .
Isochrone fitting was applied to the cleaned cluster sequence , yielding a distance modulus of ( m - M ) _ { V } ^ { 0 } = 11.35 \pm 0.10 mag and a total foreground reddening of E ( V - R ) = 0.062 \pm 0.002 mag .
Light-curve solutions were obtained for eight W Ursae Majoris eclipsing-binary systems ( W UMas ) and their orbital parameters were estimated .
Using the latter parameters , we estimate a distance to the W UMas which is independent of the host cluster ’ s physical properties .
Based on combined fits to six of the W UMas ( EP Cep , EQ Cep , ES Cep , V369 Cep , and—for the first time—V370 Cep and V782 Cep ) , we obtain an average distance modulus of ( m - M ) _ { V } ^ { 0 } = 11.31 \pm 0.08 mag , which is comparable with that resulting from our isochrone fits .
These six W UMas exhibit an obvious period–luminosity relation .
We derive more accurate physical parameters for the W UMa systems and discuss their initial masses and ages .
The former show that these W UMa systems have likely undergone angular-momentum evolution within a convective envelope ( W-type evolution ) .
The ages of the W UMa systems agree well with the cluster ’ s age .