TRACKING THE DISTRIBUTION OF 26 Al AND 60 Fe DURING THE EARLY PHASES OF STAR AND DISK EVOLUTION

Abstract

The short-lived 26 Al and 60 Fe radionuclides are synthesized and expelled into the interstellar medium by core-collapse supernova events. The solar system’s first solids, calcium–aluminum refractory inclusions (CAIs), contain evidence for the former presence of the 26 Al nuclide defining the canonical 26 Al/ 27 Al ratio of . A different class of objects temporally related to canonical CAIs are CAIs with fractionation and unidentified nuclear effects (FUN CAIs), which record a low initial 26 Al/ 27 Al of 10 −6 . The contrasting level of 26 Al between these objects is often interpreted as reflecting the admixing of the 26 Al nuclides during the early formative phase of the Sun. We use giant molecular cloud scale adaptive mesh-refinement numerical simulations to trace the abundance of 26 Al and 60 Fe in star-forming gas during the early stages of accretion of individual low-mass protostars. We find that the 26 Al/ 27 Al and 60 Fe/ 56 Fe ratios of accreting gas within a vicinity of 1000 au of the stars follow the predicted decay curves of the initial abundances at the time of star formation without evidence of spatial or temporal heterogeneities for the first 100 kyr of star formation. Therefore, the observed differences in 26 Al/ 27 Al ratios between FUN and canonical CAIs are likely not caused by admixing of supernova material during the early evolution of the proto-Sun. Selective thermal processing of dust grains is a more viable scenario to account for the heterogeneity in 26 Al/ 27 Al ratios at the time of solar system formation.