Presolar grains oxides

The discovery happened by accident. Lewis and Anders were frustrated by their failure to find the carrier of anomalous xenon in carbonaceous chondrites. They decided to try an extreme treatment to see if they could dissolve the carrier. They treated a sample of the colloidal fraction of an Allende residue with the harshest chemical oxidant known, hot perchloric acid. The black residue turned white, and to their surprise, when they measured it, the anomalous xenon was still there The residue consisted entirely of carbon, and when they performed electron diffraction measurements on it, they found that it consisted of tiny (nanometer sized) diamonds. After a detailed characterization that included chemical, structural, and isotopic studies, they reported the discovery of presolar diamond in early 1987 (Lewis et al., 1987). The 23-year search for the carrier of CCFXe (Xe-HL) was over, and the study of presolar grains had begun. 

Matrix minerals are complex mixtures of silicates (especially olivine and pyroxene), oxides, sulfides, metal, phyllosilicates, and carbonates. The bulk chemical composition of matrix is broadly chondritic, and richer in volatile elements than the other chondrite components. Some chondrules have rims of adhering matrix that appear to have been accreted onto them prior to final assembly of the meteorite. Small lumps of matrix also occur in many chondrites. Presolar grains, described in Chapter 5, occur in the matrix. 

There is clear evidence that live 26A1 was incorporated into presolar silicon carbide and aluminum oxide grains (see Chapter 5). These grains acquired their 26 Al in the atmospheres of the dying stars in which they formed. It had almost certainly decayed away long before the grains reached the solar system. In presolar grains,26 Al serves as a probe of nucleosynthesis in the parent stars. 

Compared to carbonaceous presolar grains much less isotope information, mostly for the major elements, is available for O-rich presolar dust (Lodders Amari 2005 Zinner 2007). This has several reasons. Other than presolar SiC and graphite, presolar oxides have only low trace-element concentrations. Moreover, it is not possible to produce chemical separates that consist mostly of presolar oxide grains. Presolar silicates can be found only in situ by ion imaging (see Appendix 2), a time-consuming task. The O-isotopic data of refractory oxides (corundum and other... 

Presolar stardust grains diamond, graphite, carbides and oxides... 

Most presolar silicon carbide and oxide grains and a significant fraction of presolar silicate grains found in meteorites come from low- to intermediate-mass stars in the asymptotic giant branch (AGB) phase (see Chapter 3). Evidence for this conclusion derives from two sources (1) spectroscopic observations of the envelopes of these stars and (2) comparison... 

Oxygen isotopic compositions of presolar oxide grains compared with those of red giant stars. Stellar data are shown without error bars, which are large on this scale. Both data sets are characterized by higher 170/160 ratios and lower 180/160 ratios compared to solar oxygen. Stellar data from Smith and Lambert (1990). 

Nittler, L. R. (1997) Pre solar oxide grains in meteorites. In Astrophysical Implications of the Laboratory Study of Presolar Materials, T. J. Bematowicz E. K. Zinner, Eds., pp. 59-84. AIP Conf. Proc. 402. 

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