Diagnosing the Stellar Population and Tidal Structure of the Blanco 1 Star Cluster

We present the stellar population, using Gaia DR2 parallax, kinematics, and photometry, of the young (∼100 Myr), nearby (∼230 pc) open cluster, Blanco 1. A total of 644 member candidates are identified via the unsupervised machine learning method StarGO to find the clustering in the five-dimensional position and proper motion parameter (X, Y, Z, ${\mu }_{\alpha }\cos \delta $ , μ_δ) space. Within the tidal radius of 10.0 ± 0.3 pc, there are 488 member candidates, 3 times more than those outside. A leading tail and a trailing tail, each of 50-60 pc in the Galactic plane, are found for the first time for this cluster, with stars further from the cluster center streaming away faster, manifest stellar stripping. Blanco 1 has a total detected mass of 285 ± 32 M_⊙ with a mass function consistent with a slope of α = 1.35 ± 0.2 in the sense of ${dN}/{dm}\propto {m}^{-\alpha }$ , in the mass range of 0.25-2.51 M_⊙, where N is the number of members and m is stellar mass. A minimum spanning tree (Λ_MSR) analysis shows the cluster to be moderately mass segregated among the most massive members (≳1.4 M_⊙), suggesting an early stage of dynamical disintegration.