Measurements of presolar grains

Abstract

Primitive solar system materials contain nanometerto micrometer-sized presolar grains that formed in the winds of evolved stars or in the ejecta of stellar explosions. Laboratory studies of individual presolar grains have provided a wealth of astrophysical information, such as on stellar nucleosynthesis and evolution, mixing in stars, Galactic chemical evolution, grain formation in stellar environments, chemical and physical processes in the ISM, and on the types of stars that contributed dust to the Solar System. Among the identified presolar minerals are silicon carbide (SiC), graphite, silicon nitride, refractory oxides, and silicates. The isotopic ratios of the major and minor elements in presolar grains range over many orders of magnitude, indicative of contributions from different stellar sources. Most presolar SiC (>90 %) and oxide/silicate (ca. 90 %) grains apparently formed in the winds of lowto intermediate-mass AGB stars, as inferred mainly from heavy element isotopic compositions (SiC) and, respectively, O-isotopic ratios (oxides/silicates). Although less abundant than grains from AGB stars, grains from Type II supernovae (SNe) are of particular importance. These grains incorporated matter from the outer H-rich zone down to the innermost Ni-rich zone in variable proportions, as indicated by specific isotopic fingerprints. A couple of recent findings have advanced our understanding of SN grains, providing new insights into SN nucleosynthesis, chemistry, and dust formation.