Gaia DR2 5856528760997169536 , the SIMBAD biblio

Membership determination of open clusters in high-noise environments is still an open question. This paper aims to evaluate the effectiveness of the Gaussian mixture model (GMM) in segregating likely cluster members of open clusters in high-noise environments. We use the GMM method to segregate likely cluster members of four low Galactic latitude open clusters: NGC 2112, NGC 2477, NGC 7789, and Collinder 261, based on the high-precision astrometric data of the Gaia Data Release 2 (Gaia-DR2). The GMM method is used to calculate the membership probabilities of the stars in the field of each cluster; five astrometric parameters (positions, parallaxes, and proper motions) are taken into account. We quantitatively evaluate the goodness of the cluster-field segregation for each cluster, and find that the GMM method is effective for segregating likely cluster members of these clusters, even if these clusters suffer from heavy field star contamination. We estimate the distances and absolute proper motions of these clusters using reliable cluster members; our results suggest the existence of a significant zero-point offset in Gaia-DR2 parallaxes. NGC 2112, NGC 2477, NGC 7789, and Collinder 261 are found to have a mean distance of <D>=1104±4,1437±2,2067±4 and 2802 ± 21 pc, respectively. Mean proper motions of (<µ_αcosδ>, <µ_δ>)=(-2.714±0.012,4.272±0.012), (-2.449 ± 0.006,0.876 ± 0.006), (-0.919 ± 0.004,-1.938 ± 0.004), and (-6.348 ± 0.006,-2.714 ± 0.006) mas/yr are determined for NGC 2112, NGC 2477, NGC 7789, and Collinder 261, respectively.