Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd..11e..26o&link_type=abstract
Pre-Solar Grains as Astrophysical Tools, 26th meeting of the IAU, Joint Discussion 11, 21 August 2006, Prague, Czech Republic, J
Astronomy and Astrophysics
Astrophysics
Scientific paper
It is almost twenty years since the first discovery in 1987 of surviving pre-solar minerals (diamond and silicon carbide) in primitive meteorites, followed by others (graphite, refractory oxides and nitrides, and finally silicates) in the years since. Pre-solar grains occur in even higher abundance in interplanetary dust particles (IDPs). The result is a kind of "new astronomy" based on the study of circum-stellar condensates with all the methods available to modern analytical laboratories. Central to the identification of circum-stellar minerals is the determination of isotopic compositions, which in some elements strongly deviate from the normal (Solar System) composition. While for the rarest elements still only "bulk analysis" of extracted pre-solar materials is possible, modern tools (e.g., Nano-SIMS) allow the isotopic analysis of many elements in individual sub-µm size grains, sometimes even "in situ" without extraction from the host meteorites or IDPs. The results from isotopic studies are also those that bear strongest on astrophysics. For one, they allow to pinpoint the grains' stellar sources among which Red Giants play a prominent role. In addition, given the precision of the laboratory isotopic analyses, which far exceed whatever can be hoped for in remote analyses, they allow conclusions with regard to details of nucleosynthesis and mixing in the parent stars as well as Galactic Chemical Evolution. They have borne strong on, e.g. the need for an extra mixing process (cool bottom processing) in Red Giants and provide detailed constraints on the operation of the s-process in AGB stars. A non-standard neutron capture process ("neutron burst") may be implied by the SiC-X grains from supernovae. The progress in analytical techniques promises more important results in the near future. Other astrophysical aspects, for which the study of the grains has been less fully exploited, concern the process and time scale of grain formation around the parent stars as well the constraints on interstellar dust dynamics implied by the apparently young age of the grains at the time they entered the Solar System.
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