2017PASP..129k4101W

In this paper, we analyze the open cluster NGC 1039. This young open cluster is observed as a part of Beijing-Arizona-Taiwan-Connecticut Multicolor Sky Survey. Combining our observations with the Sloan Digital Sky Survey photometric data, we employ the Padova stellar model and the zero-age main-sequence curve to the data to derive a reddening, E(B-V)=0.10±0.02, and a distance modulus, (m-M)₀=8.4±0.2, for NGC 1039. The photometric membership probabilities of stars in the region of NGC 1039 are derived using the spectral energy distribution-fitting method. According to the membership probabilities (P_SED) obtained here, 582 stars are cluster members with P_SED larger than 60%. In addition, we determine the structural parameters of NGC 1039 by fitting its radial density profile with the King model. These parameters are a core radius, R_c=4.44±1.31 pc; a tidal radius, R_t=13.57±4.85 pc; and a concentration parameter of C₀=log(R_t/R_c)=0.49±0.20. We also fit the observed mass function of NGC 1039 with masses from 0.3 M_☉ to 1.65 M_☉ with a power-law function Φ(m)∝m^α^ to derive its slopes of mass functions of different spatial regions. The results obtained here show that the slope of the mass function of NGC 1039 is flatter in the central regions (α = 0.117), becomes steeper at larger radii (α = -2.878), and breaks at m_break~0.80 M_☉. In particular, for the first time, our results show that the mass segregation appears in NGC 1039.