Context . The fraction of binary stars is an important ingredient to interpret globular cluster dynamical evolution and their stellar population . Aims . We investigate the properties of main-sequence binaries measured in a uniform photometric sample of 59 Galactic globular clusters that were observed by HST WFC/ACS as a part of the Globular Cluster Treasury project . Methods . We measured the fraction of binaries and the distribution of mass-ratio as a function of radial location within the cluster , from the central core to beyond the half-mass radius .
We studied the radial distribution of binary stars , and the distribution of stellar mass ratios .
We investigated monovariate relations between the fraction of binaries and the main parameters of their host clusters . Results . We found that in nearly all the clusters , the total fraction of binaries is significantly smaller than the fraction of binaries in the field , with a few exceptions only .
Binary stars are significantly more centrally concentrated than single MS stars in most of the clusters studied in this paper .
The distribution of the mass ratio is generally flat ( for mass-ratio parameter q > 0.5 ) .
We found a significant anti-correlation between the binary fraction in a cluster and its absolute luminosity ( mass ) .
Some , less significant correlation with the collisional parameter , the central stellar density , and the central velocity dispersion are present .
There is no statistically significant relation between the binary fraction and other cluster parameters .
We confirm the correlation between the binary fraction and the fraction of blue stragglers in the cluster .