Gaia structural parameters of 256 open clusters

In order to study the extended structure beyond the core radius of the cluster (~10pc), based on Gaia Early Data Release 3, taking up to 50pc as the searching radius, we use the pyUPMASK algorithm to redetermine the member stars of the open cluster within 1-2kpc.

We obtain the member stars of 256 open clusters, especially those located in the outer halo region of open clusters. Furthermore, we find that the radial density profile in the outer region for most open clusters deviates from the Kings profile. In order to better describe the internal and external structural characteristics of open clusters, we propose a two-component model: a core component with a King model distribution and an outer halo component with a logarithmic Gaussian distribution, and then suggest using four radii (rc, rt, ro, re) for describing the structure and distribution profile of star clusters, where rt and re represent the boundaries of the core component and outer halo component, respectively.