The fraction of binary systems in the core of thirteen low-density Galactic globular clusters

TL;DR

This study measures the binary star fraction in thirteen low-density Galactic globular clusters using HST data, revealing a minimum of 6% and a range up to 50%, with evidence of binary disruption over time.

Contribution

It provides the first detailed measurement of binary fractions in low-density globular clusters and shows their dependence on cluster age and dynamical evolution.

Findings

All clusters have at least 6% binary fraction in the core.

Binary fractions range from 10% to 50% across clusters.

Binary disruption correlates with cluster age.

Abstract

We used deep observations collected with ACS@HST to derive the fraction of binary systems in a sample of thirteen low-density Galactic globular clusters. By analysing the color distribution of Main Sequence stars we derived the minimum fraction of binary systems required to reproduce the observed color-magnitude diagram morphologies. We found that all the analysed globular clusters contain a minimum binary fraction larger than 6% within the core radius. The estimated global fractions of binary systems range from 10% to 50% depending on the cluster. A dependence of the relative fraction of binary systems on the cluster age has been detected, suggesting that the binary disruption process within the cluster core is active and can significantly reduce the binary content in time.