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

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 ⁹⁹Ru that is explained by the in situ decay of technetium isotope ⁹⁹Tc 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 ⁹⁹Tc produced in such stars is insufficient to have left a detectable ⁹⁹Ru anomaly in early solar system materials.