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تسجيل مستخدم جديدPhysical parameter study of eight W Ursae Majoris-type contact binaries in NGC 188
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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)0V = 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 clusters 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)0V = 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 clusters age.
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