Cluster aggregates surrounding Pismis 5 in the Vela molecular ridge

Abstract

Context. In the Gaia era, the precision of astrometric data is unprecedented. High-quality data make it easier to find more cluster aggregates and gather further confirmation of these open clusters. Aims. We use Gaia Data Release 3 (DR3) to redetermine the open clusters surrounding Pismis 5 in the Vela molecular ridge (VMR). We also investigate the basic properties of these clusters. Methods. We applied two clustering algorithms (STARGO and pyUPMASK) to identify the open-cluster members in five-dimensional space with α, δ, ϖ, μαcos δ, and μδ. Results. We identify eight open clusters surrounding Pismis 5 in the VMR. The open cluster QZ 1 is newly discovered. As a result of our investigation of the comprehensive properties of the clusters, we present one open binary cluster candidate (Alessi 43 and Collinder 197) and one triple open-cluster candidate (Pismis 5, Pismis 5A, and Pismis 5B). Conclusions. We identify binary and triple open-cluster candidates as potential primordial aggregates based on their similar age, position, and motion. According to kinematic speculations, the two aggregate candidates will gradually separate, and their interiors will slowly disintegrate.