Constraints on blue straggler formation mechanisms in Galactic globular clusters from proper motion velocity distributions

For a sample of 38 Galactic globular clusters(GCs), we confront the observed distributions of blue straggler(BS) proper motionsand masses (derived from isochronefitting) from the BS catalog of Simunovic & Puzia with theoretical predictions for each of the two main competing BS formation mechanisms. These are mass transfer from an evolved donor on to a main-sequence(MS) star in a close binary system, and direct collisions involving MS stars during binary encounters. We use the \texttt{FEWBODY} code to perform simulations of single-binary and binary-binary interactions. This provides collisionalvelocity and mass distributionsfor comparison to the observed distributions. Most clusters are consistent with BSs derived from a dynamically relaxedpopulation, supportive of the binary mass-transfer scenario. In a few clusters, including all the post-core collapse clusters in our sample, the collisionalvelocities provide the best fit.