# The origin of discrete multiple stellar populations in globular clusters

## TL;DR

This paper presents a new model explaining the discrete multiple stellar populations in globular clusters, linking star formation episodes to supernova feedback and AGB ejecta, consistent with recent observations of Mg-Al anti-correlations.

## Contribution

The study introduces a one-zone GC formation model where the maximum stellar mass depends on SFR, explaining the origin of discrete populations and their dependence on cluster mass.

## Key findings

- Discrete stellar populations arise from episodic star formation cycles.
- Low-mass GCs are less likely to have multiple populations.
- Young massive clusters may lack massive OB stars due to low m_max.

## Abstract

Recent observations have revealed that at least several old globular clusters (GCs) in the Galaxy have discrete distributions of stars along the Mg-Al anti-correlation. In order to discuss this recent observation, we construct a new one-zone GC formation model in which the maximum stellar mass (m_max) in the initial mass function (IMF) of stars in a forming GC depends on the star formation rate (SFR), as deduced from independent observations. We investigate the star formation histories of forming GCs. The principal results are as follows. About 30 Myr after the formation of the first generation (1G) of stars within a particular GC, new stars can be formed from ejecta from asymptotic giant branch (AGB) stars of 1G. However, the formation of this second generation (2G) of stars can last only for [10-20] Myr, because the most massive SNe of 2G expel all of the remaining gas. The third generation (3G) of stars are then formed from AGB ejecta ~ 30$ Myr after the truncation of 2G star formation. This cycle of star formation followed by its truncation by SNe can continue until all AGB ejecta is removed from the GC by some physical process. Thus, it is inevitable that GCs have discrete multiple stellar populations in the [Mg/Fe]-[Al/Fe] diagram. Our model predicts that low-mass GCs are unlikely to have discrete multiple stellar populations, and young massive clusters may not have massive OB stars owing to low m_max ([20-30] M_sun) during the secondary star formation.