The Blue Straggler population in the globular cluster M53 (NGC5024): a combined HST, LBT, CFHT study

TL;DR

This study combines multi-telescope observations to analyze the Blue Straggler Star population in globular cluster M53, revealing a bimodal radial distribution and providing the most detailed star density profile for this cluster.

Contribution

It presents a comprehensive multi-wavelength analysis of M53's BSS population and offers the most extended star density profile, highlighting discrepancies in dynamical friction effects.

Findings

BSS population of nearly 200 stars identified

Bimodal radial distribution with a dip at ~60''

Star density profile fits a King Model with extended core

Abstract

We used a proper combination of multiband high-resolution and wide field multi-wavelength observations collected at three different telescopes (HST, LBT and CFHT) to probe Blue Straggler Star (BSS) populations in the globular cluster M53. Almost 200 BSS have been identified over the entire cluster extension. The radial distribution of these stars has been found to be bimodal (similarly to that of several other clusters) with a prominent dip at ~60'' (~2 r_c) from the cluster center. This value turns out to be a factor of two smaller than the radius of avoidance (r_avoid, the radius within which all the stars of ~1.2 M_sun have sunk to the core because of dynamical friction effects in an Hubble time). While in most of the clusters with a bimodal BSS radial distribution, r_avoid has been found to be located in the region of the observed minimum, this is the second case (after NGC6388) where this discrepancy is noted. This evidence suggests that in a few clusters the dynamical friction seems to be somehow less efficient than expected. We have also used this data base to construct the radial star density profile of the cluster: this is the most extended and accurate radial profile ever published for this cluster, including detailed star counts in the very inner region. The star density profile is reproduced by a standard King Model with an extended core (~25'') and a modest value of the concentration parameter (c=1.58). A deviation from the model is noted in the most external region of the cluster (at r>6.5' from the center). This feature needs to be further investigated in order to address the possible presence of a tidal tail in this cluster.