Probing FSR star cluster candidates in bulge/disk directions with 2MASS colour-magnitude diagrams

TL;DR

This study investigates 20 star cluster candidates in the Galactic bulge and disk directions using 2MASS colour-magnitude diagrams and radial density profiles, confirming some as real clusters and identifying others as field fluctuations.

Contribution

It applies a decontamination method to distinguish genuine star clusters from field fluctuations in dense Galactic regions, confirming 6 clusters and classifying others as uncertain or non-clusters.

Findings

Confirmed 6 star clusters in the sample.

Identified 5 uncertain cases needing further observation.

Recognized 9 objects as likely field density fluctuations.

Abstract

We analyse 20 star cluster candidates projected mostly in the bulge direction ($|\ell|<60^\circ$). The sample contains all candidates in that sector classified by \citet{FSRcat} with quality flags denoting high probability of being star clusters. Bulge contamination in the colour-magnitude diagrams (CMDs) is in general important, while at lower Galactic latitudes disk stars contribute as well. Properties of the candidates are investigated with 2MASS CMDs and stellar radial density profiles (RDPs) built with field star decontaminated photometry. To uncover the nature of the structures we decontaminate the CMDs from field stars using tools that we previously developed to deal with objects in dense fields. We confirm in all cases excesses in the RDPs with respect to the background level, as expected from the method the candidates were originally selected. CMDs and RDPs taken together revealed 6 open clusters, 5 uncertain cases that require deeper observations, while 9 objects are possibly field density fluctuations.