NTT follow-up observations of star cluster candidates from the FSR catalogue

TL;DR

This study uses deep near-infrared imaging to classify 14 star cluster candidates from the FSR catalogue, successfully identifying various types of clusters and demonstrating the effectiveness of combined density and colour analysis.

Contribution

It presents a new method combining star density maps and colour-magnitude diagrams for reliable classification of star cluster candidates.

Findings

Identified 2 young clusters with massive stars

Found 3 intermediate age open clusters

Disproved FSR1767 as a star cluster

Abstract

We are conducting a large program to classify newly discovered Milky Way star cluster candidates from the list of Froebrich, Scholz & Raftery (2007). Here we present deep NIR follow-up observations from ESO/NTT of 14 star cluster candidates. We show that the combined analysis of star density maps and colour-colour/magnitude diagrams derived from deep near-infrared imaging is a viable tool to reliably classify new stellar clusters. This allowed us to identify two young clusters with massive stars, three intermediate age open clusters, and two globular cluster candidates among our targets. The remaining seven objects are unlikely to be stellar clusters. Among them is the object FSR1767 which has previously been identified as a globular cluster using 2MASS data by Bonatto et al. (2007). Our new analysis shows that FSR1767 is not a star cluster. We also summarise the currently available follow-up analysis of the FSR candidates and conclude that this catalogue may contain a large number of new stellar clusters, probably dominated by old open clusters.