Spatial mixing of binary stars in multiple-population globular clusters.

We present the results of a study aimed at investigating the effects of dynamical evolution on the spatial distribution and mixing of primordial binary starsin multiple-population globular clusters. Multiple stellar populationformation models predict that second-generation ( SG) stars form segregated in the inner regions of a more extended first-generation (FG) cluster. Our study, based on the results of a survey of N-body simulations, shows that the spatial mixing process for binary starsis more complex than that of single stars since additional processes such as binary ionization, recoiland ejection following binary-single and binary-binary interactions play a key role in determining the spatial distribution of the population of surviving binaries. The efficiency and relative importance of these additional effects depends on the binary binding energy and determines the timescale of the spatial mixing of FG and SGbinaries. Our simulations illustrate the role of ionization, recoiland ejection combined with the effects of mass segregationdriven by two-body relaxation and show that the complex interplay of all these processes results in a significant extension of the time needed for the complete spatial mixing of FG and SGbinaries compared to that of single stars. Clustersin which FG and SGsingle stars have already reached complete spatial mixing might be characterized by a significant radial gradient in the ratio of the FG-to- SGbinary fraction. The implications of the delayed mixing of FG and SGbinaries for the differences between the kinematics of the two populations are discussed.