2007AJ....133.2061W

We present 13 band CCD intermediate-band spectrophotometry of a field centered on the open cluster NGC 7789 from 400 to nearly 1000 nm, taken with the Beijing-Arizona-Taiwan-Connecticut (BATC) Multi-Color Survey photometric system. By comparing observed spectral energy distributions of NGC 7789 stars with theoretical ones, the fundamental parameters of this cluster are derived: an age of 1.4±0.1 Gyr, a distance modulus (m-M)₀=11.27±0.04, a reddening E(B-V)=0.28±0.02, and a metallicity with the solar composition Z=0.019. When the surface density profile for member stars with limiting magnitudes of 19.0 in the BATC e band (λ_eff=4925 Å) is fitted by a King model, a core radius R_c=7.52' and a tidal radius R_t=28.84' are derived for NGC 7789. The observed mass function (MF) for main-sequence (MS) stars of NGC 7789 with masses from 0.95 to 1.85 M_☉ is fitted with a power-law function φ(m)∝m^α, and a slope α=-0.96 is derived. Strong mass segregation in NGC 7789 is reflected in the significant variation of the concentration parameters C₀=log(R_t/R_c) for member stars of NGC 7789 within different mass ranges: C₀=1.02 for the most massive stars and C₀=0.37 for the lowest mass MS stars. Strong mass segregation in NGC 7789 is also indicated in the significant variation of the slopes α in different spatial regions of the cluster: the MF for stars within the core region has α=-0.71, much flatter than that for stars in external regions of the cluster (α=-1.20).