Short-lived radioisotopic enrichment from AGB interlopers in low-mass star-forming regions

ABSTRACT The decay of short-lived radioisotopes (SLRs) can be a significant source of heating early in protoplanetary systems, though how a protoplanetary disc becomes enriched with these SLRs far above the galactic background level remains an open question. Observational evidence suggests that this enrichment occurs during the period from when the disc forms to when it progresses into a protoplanetary system, and is homogenous throughout the resultant planetary system. Whilst SLRs such as $^{26}\text{Al}$ and $^{60}\text{Fe}$ can be injected into discs through interaction with Wolf–Rayet winds and supernovae, these outflows can disrupt discs, and in the case of low-mass star-forming regions high-mass stars may not form at all. Recent research has determined the existence of AGB ‘interlopers’, asymptotic giant branch stars that pass close to or through star-forming regions that could be an alternative source of SLR enrichment to Wolf-Rayet (WR) winds and supernovae. In this paper, we study the effect of AGB interlopers on star-forming regions from a dynamical perspective, determining the enrichment amount of $^{26}\text{Al}$ and $^{60}\text{Fe}$ in discs within small clusters via numerous N-body simulations via a parameter space exploration. We find that enrichment is widespread from AGB stars, with efficient enrichment dependent on the time at which the interloper intersects the star-forming region. Velocity is a factor, though interlopers travelling at 30 km s$^{-1}$ are capable of enriching many discs in a star-forming region assuming they encounter a disc when the interloper is more evolved.