Assessing the physical reality of Milky Way open cluster candidates

TL;DR

This study analyzes eleven Milky Way open cluster candidates using statistical models to determine their properties, revealing they are likely sparse star groups rather than true clusters.

Contribution

The paper introduces a method employing extreme deconvolution Gaussian mixture models to assess the physical reality of open cluster candidates.

Findings

Intrinsic age dispersions are larger than typical open clusters.

Candidates show star gathering in proper motion plane.

They are likely sparse star groups, not true clusters.

Abstract

We report results on the analysis of eleven new Milky Way open cluster candidates, recently discovered from the detection of stellar overdensities in the Vector Point diagram, by employing extreme deconvolution Gaussian mixture models. We treated these objects as real open clusters and derived their fundamental properties with their associated intrinsic dispersions by exploring the parameter space through the minimization of likelihood functions on generated synthetic colour-magnitude diagrams (CMDs). The intrinsic dispersions of the resulting ages turned out to be much larger than those usually obtained for open clusters. Indeed, they resemble those of ages and metallicities of composite star field populations. We also traced their stellar number density profiles and mass functions, derived their total masses, Jacobi and tidal radii, which helped us as criteria while assessing their physical nature as real open clusters. Because the eleven candidates show a clear gathering of stars in the proper motion plane and some hint for similar distances, we concluded that they are possibly sparse groups of stars.