2019MNRAS.486.5405G

In this paper, we investigate membership and fundamental astrophysical parameters of the nearby, intermediate-age Praesepe star cluster (M44) based on the Gaia data release 2 (Gaia-DR2). Based on 54 425 stars within a sky area of 5.5° radius, we identify 1111 likely cluster members (>=0.6) in an 11D parameter space based on a combined machine-learning method. Of these cluster members, 1052 stars are identified as high-probability (>0.8) members. We identify 13 white dwarf (WD) candidates and one M dwarf candidate in the cluster, one of the 13 WD candidates has never been reported before. The updated member list with high-precision astrometric and photometric data allows us to more precisely determine the fundamental astrophysical parameters of the cluster. We find significant correlations between the parallaxes and proper motions of the cluster members, which may be caused by the depth effect along the line-of-sight direction. We also find clear evidence for the existence of mass segregation in the cluster. Using a Monte Carlo simulation technique, the most likely distance, proper motion, and radial velocity of the cluster are determined to be <D> = 187.0 ± 0.2 pc, (<µ_αcosδ> , <µ_δ> ) = (-36.136 ± 0.020, -12.950 ± 0.014) mas yr^–1, and <RV> = + 35.0 ± 0.1 km s^–1, respectively. The core and limiting radius of the cluster are determined to be 29.9 ± 1.5 (1.6 pc) and 208.1 ± 12.6 arcmin (11.3 pc), respectively. We find that the low-mass MD candidate may be escaping from the cluster according to its present spatial positions and velocity. In addition, the total mass of the cluster within the limiting radius is determined to be 568 ± 105 M_☉ using the Monte Carlo simulation technique.