MOCCA: dynamics and evolution of single and binary stars of multiple stellar populations in tidally filling and underfilling globular star clusters

We present an upgraded version of the MOCCA code for the study of dynamical evolution of globular clusters (GCs) and its first application to the study of evolution of multiple stellar populations. We explore initial conditions spanning different structural parameters for the first (FG) and second generation of stars (SG) and we analyse their effect on the binary dynamics and survival. Here, we focus on the number ratio of FG and SG binaries, their spatial variation, and the way their abundances are affected by various cluster initial properties. We find that present-day SG stars are more abundant in clusters that were initially tidally filling. Conversely, FG stars stay more abundant in clusters that were initially tidally underfilling. We find that the ratio between binary fractions is not affected by the way we calculate these fractions [e.g. only main-sequence binaries (MS) or observational binaries, i.e. MS stars >0.4 M-circle dot mass ratios >0.5]. This implies that the MS stars themselves are a very good proxy for probing entire populations of FG and SG. We also discuss how it relates to the observations of Milky Way GCs. We show that MOCCA models are able to reproduce the observed range of SG fractions for Milky Way GCs for which we know these fractions. We show how the SG fractions depend on the initial conditions and provide some constraints for the initial conditions to have more numerous FG or SG stars at the Hubble time.

Automated summary

We present an upgraded version of the MOCCA code for the study of dynamical evolution of globular clusters and its first application to the study of evolution of multiple stellar populations. The study explores the effects of different initial conditions on binary dynamics and survival, focusing on the number ratio and spatial variation of binaries, as well as their abundances. The findings highlight the abundance differences between first generation (FG) and second generation (SG) stars and demonstrate that MS stars can serve as proxies for the entire populations of FG and SG.