Parallax distribution of core member candidates selected by the proper motion criteria. Left panel: histogram of parallax ϖ that can be fitted by a single Gaussian profile. The distribution of relative deviation of ϖ is shown in the central panel; the red dashed curve represents the acceptable maximum σ_ϖ/ϖ boundary, which includes 68% of the candidates in the histogram. Right panel: the parallax criteria is indicated with the red dashed curve.