The dynamical state of the globular clusters Rup 106 and IC 4499

TL;DR

This study assesses the dynamical age of globular clusters Rup 106 and IC 4499 using Blue Straggler Stars and mass function slopes, revealing they are relatively young with early signs of mass segregation.

Contribution

It introduces observational methods using Blue Straggler distribution and mass function slopes to determine the dynamical age of globular clusters.

Findings

Both clusters are dynamically young with initial mass segregation.

Blue Straggler stars are more centrally concentrated than other stars.

Mass function slopes decrease with cluster-centric distance.

Abstract

The dynamical evolution of globular clusters is theoretically described by a series of well known events typical of N-body systems. Still, the identification of observational signatures able to empirically describe the stage of dynamical evolution of a stellar system of the density typical of a globular cluster, represents a challenge. In this paper we study the dynamical age of the globular clusters Rup 106 and IC 4499. To this aim, we study the radial distribution of the Blue Straggler Stars via the A+ parameter and of the slope of the Main Sequence Mass Function. Both tracers show that Rup 106 and IC 4499 are dynamically young clusters where dynamical friction has just started to segregate massive stars towards the clusters' centre. In fact, we observe that the Blue Straggler stars are more centrally concentrated in both clusters than the reference population. On the same line, we find that in both cases the slope of the mass function significantly decreases as a function of the cluster-centric distances. This result provides additional support for the use of the the radial distribution of the blue stragglers as a powerful observationally convenient indicator of the cluster dynamical age.