The X-ray Source Population of the Metal-Rich Globular Cluster NGC 6528

TL;DR

This study investigates the X-ray sources in the metal-rich globular cluster NGC 6528, identifying 18 sources and classifying them, revealing insights into how metallicity and dynamical evolution influence X-ray populations.

Contribution

First detailed analysis of X-ray sources in NGC 6528, combining Chandra and Hubble data to classify sources and assess effects of metallicity and dynamical evolution.

Findings

Identified 18 X-ray sources within the cluster.

Classified sources as cataclysmic variables and active binaries.

High metallicity's X-ray enhancement is offset by dynamical effects.

Abstract

We present the first study of the X-ray sources in one of the most metal-rich globular clusters in the Galaxy, NGC 6528. Using relatively deep (66 ksec) archival imaging from the Chandra X-ray Observatory, we identify 18 sources within the half-light radius of the cluster, all in the range $L_X \sim 10^{31}$-$10^{32}$erg s$^{-1}$ (0.5-7 keV). By combining these data with photometry from the Hubble Space Telescope and other sources, we classify the X-ray sources as a likely mix of cataclysmic variables and active binaries, though one or more of the brighter objects could be a quiescent low-mass X-ray binary. For this cluster, it appears that the X-ray binary-enhancing effects of high metallicity are outweighed by the cluster's advanced dynamical evolution, leading to a relatively modest X-ray source population.