HST survey of Magellanic Cloud star clusters

We derived MFs accounting for unresolved binaries and identified candidate BS populations from color-magnitude diagrams. The fraction of binaries with q>0.7 ranges from 5% in NGC 2121 up to 13% in NGC 2173, with a mass-ratio distribution that is consistent with being flat on average. By combining our results with literature data, we confirm a clear anticorrelation between the core binary fraction and cluster mass, while no significant dependence on cluster age is found.

The clusters follow the established relation between age and core radius, although with substantial scatter at fixed age. Within the narrow age range explored here, clusters exhibiting steeper MFs are found to have smaller core radii. We find no evidence of a correlation between the fractions of binaries and BS fractions.

These findings are consistent with a scenario in which dynamical evolution plays a primary role in the formation of binary populations. The connection between MF slope and structural parameters provides new constraints on cluster evolution and suggests a link between MF slope and structural evolution.