2017MNRAS.464.4318N

The presence and abundance of short-lived radioisotopes ²⁶Al and ⁶⁰Fe in chondritic meteorites implies that the Sun formed in the vicinity of one or more massive stars that exploded as supernovae (SNe). Massive stars are more likely to form in massive star clusters (>1000 M_☉) than lower mass clusters. However, photoevaporation of protoplanetary discs from massive stars and dynamical interactions with passing stars can inhibit planet formation in clusters with radii of ∼1 pc. We investigate whether low-mass (50-200 M_☉) star clusters containing one or two massive stars are a more likely avenue for early Solar system enrichment as they are more dynamically quiescent. We analyse N-body simulations of the evolution of these low-mass clusters and find that a similar fraction of stars experience SN enrichment than in high-mass clusters, despite their lower densities. This is due to two-body relaxation, which causes a significant expansion before the first SN even in clusters with relatively low (100 stars pc^–3) initial densities. However, because of the high number of low-mass clusters containing one or two massive stars, the absolute number of enriched stars is the same, if not higher than for more populous clusters. Our results show that direct enrichment of protoplanetary discs from SNe occurs as frequently in low-mass clusters containing one or two massive stars (>20 M_☉) as in more populous star clusters (1000 M_☉). This relaxes the constraints on the direct enrichment scenario and therefore the birth environment of the Solar system.