Physical parameter study of eight W Ursae Majoris-type contact binaries in NGC 188

Abstract

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 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)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 cluster's age.

28 pages, 7 figures, accepted by AJ

References in corpus (6)

• The Dartmouth Stellar Evolution Database
• The Distances to Open Clusters from Main-Sequence Fitting. IV. Galactic Cepheids, the LMC, and the Local Distance Scale
• Luminosity function of contact binaries based on the ASAS survey
• A search for open cluster Cepheids in the Galactic plane
• Temperature Differences in the Cepheid Instability Strip Require Differences in the Period-Luminosity Relation in Slope and Zero Point
• Bayesian Investigation of Isochrone Consistency Using the Old Open Cluster NGC 188

Cited by in corpus (5)

• The Zwicky Transient Facility Catalog of Periodic Variable Stars
• UVIT Open Cluster Study. II. Detection of extremely low mass white dwarfs and post-mass transfer binaries in M67
• Investigation of the Orbital Period and Mass Relations for W UMa-type Contact Systems
• Contact Binaries as Viable Distance Indicators: New, Competitive (V)JHKs Period-Luminosity Relations
• Case AD, AR, and AS binary evolution and their possible connections with W UMa binaries