The fraction of binary systems in the core of five Galactic open clusters

TL;DR

This study measures the binary star fraction in five Galactic open clusters, revealing higher binary proportions than globular clusters and suggesting cluster mass influences binary disruption rates.

Contribution

It provides the first detailed estimates of binary fractions in open clusters using deep photometry and analyzes their dependence on cluster mass.

Findings

Binary fractions range from 35% to 70% in the clusters.

All clusters have a minimum binary fraction above 11%.

Binary disruption correlates with cluster mass.

Abstract

We used deep wide field photometric observations to derive the fraction of binary systems in a sample of five high-latitude Galactic open 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 clusters contain a minimum binary fraction larger than 11% within the core radius. The estimated global fractions of binary systems range from 35% to 70% depending on the cluster. The comparison with homogeneous estimates performed in globular clusters indicates that open clusters hold a significantly higher fraction of binary systems, as predicted by theoretical models and N-body simulations. A dependence of the relative fraction of binary systems on the cluster mass has been detected, suggesting that the binary disruption within the cluster core is the dominant process that drives the fraction of binaries in stellar systems.