Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998m%26ps...33..549z&link_type=abstract
Meteoritics & Planetary Science, vol. 33, no. 4, pp. 549-564.
Astronomy and Astrophysics
Astronomy
12
Scientific paper
A series of trends can be discerned in the study of presolar dust grains from primitive meteorites and these trends might give us hints in which direction this new field of astronomy is developing. They include: 1) A focus on ever smaller components of meteorites. 2) A shift from the study of the elemental abundances in the solar system to the study of isotopic abundances. 3) A shift of emphasis from averages of the isotopic abundances as represented by the whole solar system to individual isotopic components preserved in circumstellar dust grains. 4) The preferential study of rare types of presolar dust grains. 5) The emergence of new technical capabilities for the study of individual presolar dust grains. Examples include isotopic imaging and resonance ionization mass spectrometry (RIMS). 6) A shift from a situation in which grain data confirm previously held theoretical ideas to a situation in which the experimental data impose new constraints on theoretical models of nucleosynthesis, stellar mixing and grain formation in stellar outflows. In other words, the data do not confirm but drive the theory. An example is the distribution of Si isotopic ratios in individual mainstream SiC grains for which many different theoretical explanations have been offered. There are still many unsolved problems posed by the grain data, the most difficult being the interpretation of the isotopic ratios of grains with a supernova signature (evidence for 44Ti and excesses in 28Si) in terms of theoretical models of nucleosynthesis and the mixing of supernova ejecta. Future progress is expected to come from the analysis of larger number of grains, the search for new types of presolar grains, the analysis of smaller grains and of more elements in a given grain, both made possible by increase of sensitivity of ion microprobes and the extended application of RIMS, from multi-dimensional models of stellar evolution with enlarged nuclear networks, and from new measurements of nuclear cross sections.
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