TEM studies of circumstellar dust

Abstract

In recent years the development of special chemical separation techniques has permitted the isolation of material from primitive meteorites that can be unambiguously identified as pre-solar grains-that is, solids that condensed in the atmospheres of ancient stars and later became incorporated into the cloud of gas and dust which gave rise to our solar system. This identification is made possible in part by development of sophisticated mass spectrometry techniques for the analysis of ensembles of these grains and in part by ion microprobe techniques for determining the isotopic structures in single micron-sized grains. In particular, meteoritic grains which have isotopic compositions radically different from the solar system average can be assigned a pre-solar origin. In some cases, plausible astrophysical sites can be identified: for example, isotopic structures of Kr, Xe, Ba, and Nd in some grains resemble those expected to be produced by s-process nucleosynthesis in asymptotic giant branch (AGB) stars.