A. P. Milone, G. Piotto, L. R. Bedin, A. Aparicio, J. Anderson, A. Sarajedini, A. F. Marino, A. Moretti, M. B. Davies, B. Chaboyer, A. Dotter, M. Hempel, A. Marin-Franch, S. Majewski, N. E. Q. Paust, I. N. Reid, A. Rosenberg, M. Siegel
The fraction of binary stars is an important ingredient to interpret globular
cluster dynamical evolution and their stellar population. 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. 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. 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.
View original:
http://arxiv.org/abs/1111.0552
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