Investigating Galactic binary cluster candidates with Gaia EDR3

TL;DR

This study uses Gaia EDR3 data to identify and analyze stellar open cluster pairs in the Milky Way, revealing their physical states, interactions, and structural properties, and providing insights into cluster pair formation and evolution.

Contribution

First comprehensive analysis of open cluster pairs in Gaia EDR3, characterizing their physical and dynamical properties and interactions in the Milky Way.

Findings

Identified 4 gravitationally bound cluster pairs.

Found 2 interacting but unbound cluster pairs.

Clusters in bound pairs show larger half-light to tidal radius ratios.

Abstract

A number of stellar open cluster (OC) pairs in the Milky Way occupy similar positions in the phase space (coordinates, parallax and proper motions) and therefore may constitute physically interacting systems. The characterization of such objects based on observational data is a fundamental step towards a proper understanding of their physical status and to investigate cluster pair formation in the Galaxy. In this work, we employed Gaia EDR3 data to investigate a set of 16 OCs distributed as seven stellar aggregates. We determined structural parameters and applied a decontamination technique that allowed to obtain unambiguous lists of member stars. The studied OCs span Galactocentric distances and ages in the ranges ~7 < $R_G$ (kpc) < ~11 and 7.3 <= log t <= 9.2. Eight OCs were found to constitute 4 gravitationally bound pairs (NGC5617-Trumpler22, Collinder394-NGC6716, Ruprecht100-Ruprecht101, NGC659-NGC663, the latter being a dynamically unevolved binary) and other 4 clusters constitute 2 interacting, but gravitationally unbound, pairs (King16-Berkeley4, NGC2383-NGC2384, the latter being a dissolving OC). Other 4 OCs (Dias1, Pismis19, Czernik20, NGC1857) seem not associated to any stellar aggregates. Apparently, clusters within bound and dynamically evolved pairs tend to present ratios of half-light to tidal radius larger than single clusters located at similar $R_G$, suggesting that mutual tidal interactions may possibly affect their structural parameters. Unbound or dynamically unevolved systems seems to present less noticeable signature of tidal forces on their structure. Moreover, the core radius seems more importantly correlated with the clusters' internal dynamical relaxation process.