MOCCA: Effects of pristine gas accretion and cluster migration on globular cluster evolution, global parameters, and multiple stellar populations

Abstract

Using the MOCCA code, we study the evolution of globular clusters (GCs) with multiple stellar populations. For this purpose, the MOCCA code has been significantly extended to take into account the formation of an enriched population of stars from re-accreted gas with a time delay after the formation of the pristine population of stars. The possibility of cluster migration in the host galaxy and the fact that the pristine population can be described by a model not in virial equilibrium are also taken into account. Gas re-accretion and cluster migration have a decisive impact on the observational parameters of clusters and the ratio of the number of objects between the pristine and enriched populations. The obtained results, together with observational data, suggest a speculative refinement of the AGB scenario that makes it possible to explain some observational data, such as the ratio of the pristine to the enriched populations, the observational fact that for some GCs the pristine population is more concentrated than the enriched one, and possibly a correlation between the ratio of the number of enriched stars to the total number of stars and the mass of the cluster. In this scenario, it is important to take into account the environment in which the cluster lives, the conditions in the galaxy when it formed, and the fact that a significant part of the GCs associated with the Galaxy come from dwarf galaxies that merged with the Milky Way. The initial conditions of GCs in our simulations differ from the widely used typical models, as they require GCs to fill the Roche lobe rather than being highly concentrated within it, imposing strong constraints on their formation locations within the galaxy.