SIGNATURES OF THE s-PROCESS IN PRESOLAR SILICON CARBIDE GRAINS: BARIUM THROUGH HAFNIUM

Isotopic and elemental abundance signatures in the mass range Ba through Hf have been determined in a silicon carbide–rich sample of the Murchison carbonaceous chondrite, using inductively coupled plasma mass spectrometry (ICP-MS). Despite the problem of some isobaric interferences, useful results were obtained for a number of isotopes. Disagreements between astrophysical predictions and previous results for Ba and Nd obtained by thermal ionization mass spectrometry are confirmed. Our data for Dy are more in line with predictions, however. The s-process signatures for several other elements in the rare earth element (REE) mass range were observed for the first time and are also consistent with theoretical predictions. The elemental abundance pattern shows deficit relative to production ratios of the more volatile REE, notably Yb, and, to a lesser extent, Sm and Eu. This may allow estimating an average condensation temperature of trace elements into SiC. Subject headinggs: meteors, meteoroids — nuclear reactions, nucleosynthesis, abundances — stars: AGB and post-AGB — stars: carbon