Binary Frequencies in Globular Clusters
  Binary stars are predicted to have an important role in the evolution of
globular clusters, so we obtained binary fractions for 35 globular clusters
that were imaged in the F606W and F814W with the ACS on the Hubble Space
Telescope. When compared to the values of prior efforts (Sollima et al. 2007;
Milone et al. 2012), we find significant discrepancies, despite each group
correcting for contamination effects and having performed the appropriate
reliability tests. The most reliable binary fractions are obtained when
restricting the binary fraction to q > 0.5. Our analysis indicates that the
range of the binary fractions is nearly an order of magnitude for the lowest
dynamical ages, suggesting that there is a broad distribution in the binary
fraction at globular cluster formation. Dynamical effects also appears to
decrease the core binary fractions by a factor of two over a Hubble time, but
this is a weak relationship. We confirm a correlation from previous work that
the binary fraction within the core radius decreases with cluster age,
indicating that younger clusters formed with higher binary fractions. The
strong radial gradient in the binary fraction with cluster radius appears to be
a consequence of dynamical interactions. It is often not present in dynamically
young clusters but nearly always present in dynamically old clusters.
