S-PROCESS ZIRCONIUM IN PRESOLAR SILICON-CARBIDE GRAINS

The isotopic composition of zirconium in silicon carbide grains from t he Murchison meteorite was measured by resonant ionization mass spectr ometry of laser-ablated neutral atoms. These grains are condensates fr om the atmospheres of red giant stars that existed before the formatio n of our sun and solar system, and they contain records of nucleosynth esis in these stars. The r-process-dominated isotope zirconium-96 was depleted by more than a factor of 2 compared with the s-process-domina ted isotopes zirconium-90, zirconium-91, zirconium-92, and zirconium-9 4, in agreement with expectations for neutron capture nucleosynthesis in asymptotic giant branch stars.