Extinct Technetium in Silicon Carbide Stardust Grains: Implications for Stellar Nucleosynthesis

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Abstract
The isotopic composition of ruthenium (Ru) in individual presolar silicon carbide (SiC) stardust grains bears the signature of s -process nucleosynthesis in asymptotic giant branch stars, plus an anomaly in 99 Ru that is explained by the in situ decay of technetium isotope 99 Tc in the grains. This finding, coupled with the observation of Tc spectral lines in certain stars, shows that the majority of presolar SiC grains come from low-mass asymptotic giant branch stars, and that the amount of 99 Tc produced in such stars is insufficient to have left a detectable 99 Ru anomaly in early solar system materials.