Dust from oxygen-rich stars

Details Dust from oxygen-rich stars Dust from oxygen-rich stars

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29q.512n&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 512

Physics

2

Chondrites, Interstellar Matter, Isotopic Enrichment, Meteoritic Composition, Oxygen Isotopes, Anomalies, Chemical Composition, Metallicity, Particle Size Distribution, Phase Transformations, Stellar Atmospheres

Scientific paper

We have previously reported the identification of 8 presolar Al-rich oxide grains out of 2000 measured in an acid residue of the Tieschitz ordinary chondrite. Continued ion imaging searches for particles with unusual O-16/O-18 ratios have located 13 more isotopically anomalous oxide grains out of an additional 4000 Tieschitz grains. This brings the number of interstellar oxide grains isolated from meteorites to date to 24 (21 from Tieschitz and 1 each from Murchison, Orgueil, and Bishunpur) and extends the study of presolar grains to samples from a range of O-rich stars. We have divided the grains into three groups on the basis of their O-isotopic ratios. Group 1 grains are characterized by large enrichments in O-17 and modest O-18 depletions, similar to spectroscopic observations of O-rich red giant stars. Group 2 grains have O-18 depletions orders of magnitude larger than those that have been observed in stellar atmospheres, as well as large enrichments in Al-26 and O-17. The stellar source(s) for the (17)O-depleted group 3 grains is difficult to ascertain. Estimates of dust production in the galaxy indicate that O-rich phases should be as abundant as C-rich phases. The abundance of demonstrably interstellar aluminum oxide grains found to date in meteorites is far less than the abundance of isotopically anomalous SiC grains or even the abundance of the less common interstellar graphite component. This is especially surprising since reduced phases should be less stable than O-rich ones in the oxidizing conditions of the solar nebula. One possible explanation for the apparent paucity of interstellar oxides is that they have a finer grain-size distribution than the reduced phases and thus may have largely escaped detection. Measurements in progress on aggregates of fine-grained Tieschitz oxides may settle this issue. Ion imaging searches of physically separated 1-2 microns Tieschitz silicate grains are currently underway.

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