2025AJ....170..172P

The outer Galaxy presents a distinctive environment for investigating star formation. This study develops a novel approach to identify true cluster members based on unsupervised clustering using astrometry with significant uncertainties. As a proof of concept, we analyze three outer Galactic young stellar object (YSO) clusters at different distances and densities within 65^∘ < l < 265^∘, each known to contain >100 members based on the Star Formation in Outer Galaxy (SFOG; E. Winston et al. catalog. The 618 YSO clusters in the SFOG data set were based on 2D clustering. In this contribution, we apply the Hierarchical Density-Based Spatial Clustering of Applications with Noise (HDBSCAN^*) algorithm to the precise Gaia DR3 astrometry to assign YSO cluster membership. A Monte Carlo simulation coupled with the HDBSCAN^* (HDBSCAN-MC algorithm) addresses YSO astrometric uncertainties through 5D clustering. We introduce the Generation Of cLuster anD FIeld STar (GOLDFIST) simulation to enable robust membership determination, performing an unsupervised clustering analysis in higher-dimensional feature space while accommodating measurement errors. In this study, we extended our approach to distant outer galaxy YSOs and clusters with larger astrometric uncertainties. The results include the discovery of new members in the previously identified clusters. We also analyze the known stars in the clusters and confirm their membership. The derived membership probabilities are included in the provided cluster catalogs. The more accurately predicted simulation distance estimates closely agree, within uncertainty limits, with the median distance estimates derived from Gaia data, and are compared with the kinematic distances from the Wide-field Infrared Survey Explorer H II survey.