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[49.06] Observational Evidence for Presolar Grains around Oxygen-rich Evolved Stars

A. K. Speck (University of Missouri - Columbia), A. M. Hofmeister (Washington University, St Louis)

Many presolar grain types have been found in meteorites since the discovery of presolar silicon carbide (SiC) grains in the Murray meteorite. Initially these were mostly limited to carbon-rich grains. However, more recently, oxygen-rich presolar grains have been isolated: corundum (Al₂O₃), spinel (MgAl₂O₄), hibonite(CaAl₁₂O₁₉) and rutile (TiO₂). The majority of these O-rich grains, like the SiC grains, have isotopic compositions indicative of formation around asymptotic giant branch (AGB) stars.

There is very little observational evidence for most of these presolar grains around AGB stars, and what little evidence does exist is generally misinterpreted. We present the observational evidence (or lack thereof) for these oxide grains, and discuss the discrepancies between meteoritic and astronomical results, as well as the problems of interpreting dust features in astronomical spectra.

At present, the only O-rich presolar grain type for which the observational evidence is not (currently) disputed is (amorphous) Al₂O₃. In order to progress further in matching these presolar grains and the grains currently forming around AGBs stars we need to know more details about these grains: e.g.\ polytypes, the level of crystallinity/amorphousness in the grains, the size distributions, etc. With this information we place more constraints on the IR spectral feature we should be looking for. Further observational constraints are also required, such as spatial correlations between related IR spectral features.

The author(s) of this abstract have provided an email address for comments about the abstract: speckan@missouri.edu

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.