Correlated molybdenum, ruthenium, and barium isotope anomalies in high-density presolar graphite grains

Abstract We have analyzed molybdenum, ruthenium, and barium isotopes simultaneously in 21 individual high-density presolar graphite grains from the Murchison CM2 meteorite using the Chicago Instrument for Laser Ionization (CHILI). While all grains clearly suffered from contamination with molybdenum of solar composition, probably from the parent asteroid of the host meteorite, six grains showed s -process enrichments in at least one of the elements analyzed, pointing toward an AGB star origin of these grains. For one of the grains, we found almost pure s -process ruthenium, challenging existing AGB star models that assume full homogenization of freshly produced s -process material in the convective AGB star envelope prior to grain condensation. Furthermore, our results indicate that these grains condensed before about half of the 99 Tc decayed to 99 Ru and that technetium did not condense into the grains.