Theoretical Distributions of Short-lived Radionuclides for Star Formation in Molecular Clouds

1Marco Fatuzzo,2,3Fred C. Adams
The Astrophysical Journal 925 56 Open Access Link to Article [DOI 10.3847/1538-4357/ac38a7]
1Department of Physics, Xavier University, Cincinnati, OH 45207, USA; fatuzzo@xavier.edu
2Department of Physics, University of Michigan, MI 48109, USA
3Department of Astronomy, University of Michigan, MI 48109, USA; fca@umich.edu

Short-lived radioactive nuclei (half-life τ1/2 ∼ 1 Myr) influence the formation of stars and planetary systems by providing sources of heating and ionization. Whereas many previous studies have focused on the possible nuclear enrichment of our own solar system, the goal of this paper is to estimate the distributions of short-lived radionuclides (SLRs) for the entire population of stars forming within a molecular cloud. Here we focus on the nuclear species 60Fe and 26Al, which have the largest impact due to their relatively high abundances. We construct molecular-cloud models and include nuclear contributions from both supernovae and stellar winds. The resulting distributions of SLRs are time dependent with widths of ∼3 orders of magnitude and mass fractions ρSLR/ρ* ∼ 10−11–10−8. Over the range of scenarios explored herein, the SLR distributions show only modest variations with the choice of cloud structure (fractal dimension), star formation history, and cluster distribution. The most important variation arises from the diffusion length scale for the transport of SLRs within the cloud. The expected SLR distributions are wide enough to include values inferred for the abundances in our solar system, although most of the stars are predicted to have smaller enrichment levels. In addition, the ratio of 60Fe/26Al is predicted to be greater than unity, on average, in contrast to solar system results. One explanation for this finding is the presence of an additional source for the 26Al isotope.

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