Star clusters forming in a low-metallicity starburst – rapid self-enrichment by (very) massive stars

Stellar winds of massive (9\, M_) and very massive (100\, M_) stars may play an important role in the metal-enrichment during the formation of star clusters. With novel high-resolution hydrodynamical griffin-project simulations, we investigate the rapid recycling of stellar wind-material during the formation of massive star clusters up to Mcluster~ 2× 10⁵\, M_ in a low-metallicity dwarf galaxy starburst. The simulation realizes new stars from a stellar initial mass function (IMF) between $0.08$ and ~ 400\, M_ and follows stellar winds, radiation and supernova-feedback of single massive stars with evolution tracks. Star clusters form on time-scales less than ∼5 Myr, and their supernova-material is very inefficiently recycled. Stellar wind-material, however, is trapped in massive clusters resulting in the formation of stars self-enriched in Na, Al, and N within only a few Myr. Wind-enriched (second population, 2P) stars can be centrally concentrated in the most massive clusters (10⁴\, M_) and the locked wind-material increases approximately as Mcluster². These trends resemble the characteristics of observed 2P stars in globular clusters (GCs). We fit scaling relations to the lognormal distributed wind-mass fractions and extrapolate to possible GC progenitors of Mcluster=10⁷\, M_ to investigate whether a dominant 2P could form. This can only happen if the IMF is well-sampled, single massive stars produce at least a factor of a few more enriched winds, for example, through a top-heavy IMF, and a significant fraction of the first population (unenriched) stars is lost during cluster evolution.