Previous | Session 28 | Next
E. Zinner (Washington University)
Primitive meteorites contain tiny specks of stardust that can be isolated and analyzed in detail in the laboratory. The study of these presolar grains, in particular measurement of their isotopic compositions, has provided a wealth of information on their stellar sources. Several types of parent stars could be identified, including AGB stars, Type II supernovae, and novae, and various constraints have been obtained on models of nucleosynthesis for these stars. Recently, a new type of ion microprobe, the NanoSIMS, has allowed the isotopic analysis of sub-micron grains and led to results that could not have been obtained before. One example is the finding that the abundance of presolar spinel grains is much higher for submicron grains than for larger grains. Mg isotopic measurements of such spinel grains revealed large inferred 26Al/27Al ratios that are much higher than predicted from shell H burning in AGB stars and indicate extra mixing (cool bottom processing). Another example is the discovery of presolar silicate dust in interplanetary dust particles, Antarctic micrometeorites and primitive meteorites. These grains are sub-micron in size. Although their abundances are higher than those of most other presolar grain types identified so far, only the analysis of many thousands of grains by high-spatial-resolution isotopic imaging has made their identification among an overwhelming majority of isotopically normal silicate grains of solar-system origin possible. A last example is the analysis of a sub-type of presolar SiC grains believed to have originated in low-metallicity AGB stars. Titanium isotopic measurements confirm such an origin and provide information on the Galactic chemical evolution of the Ti isotopes.
Previous | Session 28 | Next
Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.