Discovery of Abundant In Situ Silicate and Spinel Grains from Red Giant Stars in a Primtive Meteorite

The Astrophysical Journal (Impact Factor: 5.99). 10/2004; 613(2). DOI: 10.1086/424842
Source: OAI


We report the discovery of 12 in situ presolar silicate and spinel grains, 140-590 nm in size, in the Acfer 094 meteorite. These grains represent a matrix-normalized abundance of presolar O-rich dust of 170 parts per million. Among the 10 silicate grains are three olivines, four pyroxenes, and three grains with glasslike composition. Eleven grains have large excesses in 17O with 17O/16O ratios of up to 2.9 times the solar ratio and slightly lower than or close-to-solar 18O/16O ratios. These grains most likely formed in 1.5-1.65 Msolar red giant branch (RGB) or asymptotic giant branch (AGB) stars with close-to-solar metallicity. One pyroxene grain has close-to-solar 17O/16O and 18O/16O of 3.8 times solar. Silicon- and Fe-isotopic ratios of this grain are suggestive of the formation in an RGB or AGB star, probably with higher-than-solar metallicity. 29Si/28Si and 30Si/28Si ratios of the silicate grains vary by ~16%, are positively correlated with one another, and fall to the 30Si-poor side of the Si mainstream line characteristic for presolar SiC from AGB stars. This gives independent confirmation for the view that the Si mainstream line reflects the Galactic chemical evolution of the Si isotopes, except for a small shift due to dredge-up of matter from the He shell in AGB stars.

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Available from: Smail Mostefaoui, Oct 05, 2015
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    • "Presolar silicates: One of the most important discoveries in the field of presolar grain research in recent years was the identification of presolar silicates, first in an IDP (Messenger et al. 2003) and later also in primitive meteorites (Mostefaoui and Hoppe 2004, Nguyen and Zinner 2004) by NanoSIMS oxygen ion imaging (see Ion imaging and Figure 5). Presolar silicates were also identified in the IMS1270 ion probe equipped with a SCAPS detector (Nagashima et al. 2004); however, because of lower spatial resolution, this technique reliably identifies only the largest presolar grains (> 500 nm) or those with comparatively large isotope anomalies for which contributions from surrounding isotopically normal matter do not completely erase the isotope anomaly. "
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    ABSTRACT: The NanoSIMS ion probe is a new-generation SIMS instrument, characterised by superior spatial resolution, high sensitivity and multi-collection capability. Isotope studies of certain elements can be conducted with 50–100 nm resolution, making the NanoSIMS an indispensable tool in many research fields. We review technical aspects of the NanoSIMS ion probe and present examples of applications in cosmochemistry and biological geochemistry. This includes isotope studies of presolar (stardust) grains from primitive meteorites and of extraterrestrial organics, the search for extinct radioactive nuclides in meteoritic materials, the study of lunar samples, as well as applications in environmental microbiology, cell biology, plant and soil science, and biomineralisation.
    Geostandards and Geoanalytical Research 06/2013; 37(2). DOI:10.1111/j.1751-908X.2013.00239.x · 3.21 Impact Factor
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    • "They reveal large isotopic variations of up to several orders of magnitude that distinguish them from solar material and trace individual grains back to their specific sources. Diamond and recently discovered silicates are most abundant among presolar grains, with concentrations of more than 100 ppm in primitive meteorites and interplanetary dust particles (Anders and Zinner 1993; Nguyen and Zinner 2004; Mostefaoui and Hoppe 2004; Floss et al. 2006). The presolar SiC grains, typically making up a few ppm of the host meteorite, are separated into seven groups: types A, B, X, Y, Z, and mainstream grains and a small population of nova grains. "
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    ABSTRACT: Abstract— Thirteen presolar silicon carbide grains—three of supernova (SN) origin and ten of asymptotic giant branch (AGB) star origin—were examined with time-of-flight-secondary ion mass spectrometry (TOF-SIMS). The grains had been extracted from two different meteorites—Murchison and Tieschitz—using different acid residue methods. At high lateral resolution of ∼300 nm, isotopic and elemental heterogeneities within the micrometer-sized grains were detected. The trace elemental abundances, when displayed in two-element correlation plots, of Li, Mg, K, and Ca show a clear distinction between the two different meteoritic sources. The different concentrations might be attributed to differences of the host meteorites and/or of extraction methods whereas the stellar source seems to be less decisive. In one SN grain with 26Mg-enrichment from extinct 26Al, the acid treatment, as part of the grain separation procedure, affected the Mg/Al ratio in the outer rim and therefore the inferred initial 26Al/27Al ratio. A second SN grain exhibits a lateral heterogeneity in 26Al/27Al, which either is due to residual Al-rich contamination on the grain surface or to the condensation chemistry in the SN ejecta.
    01/2010; 42(7‐8):1121 - 1134. DOI:10.1111/j.1945-5100.2007.tb00564.x
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    • "The crystallinity of IDPs indicates that like CI material, some fraction of their constituents has been thermally processed. Also, presolar GEMS-like objects have been found in chondrite matrices (e.g., Mostefaoui and Hoppe 2004; Nguyen et al. 2005). "
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    ABSTRACT: Abstract— The matrices of all primitive chondrites contain presolar materials (circumstellar grains and interstellar organics) in roughly CI abundances, suggesting that all chondrites accreted matrix that is dominated by a CI-like component. The matrix-normalized abundances of the more volatile elements (condensation temperatures <750–800 K) in carbonaceous and ordinary chondrites are also at or slightly above CI levels. The modest excesses may be due to low levels of these elements in chondrules and associated metal. Subtraction of a CI-like matrix component from a bulk ordinary chondrite composition closely matches the average composition of chondrules determined by instrumental neutron activation analysis (INAA) if some Fe-metal is added to the chondrule composition.Measured matrix compositions are not CI-like. Sampling bias and secondary redistribution of elements may have played a role, but the best explanation is that ˜10–30% of refractory-rich, volatile depleted material was added to matrix.If most of the more volatile elements are in a CI-dominated matrix, the major and volatile element fractionations must be largely carried by chondrules. There is both direct and indirect evidence for evaporation during chondrule formation. Type IIA and type B chondrules could have formed from a mixture of CI material and material evaporated from type IA chondrules. The Mg-Si-Fe fractionations in the ordinary chondrites can be reproduced with the loss of type IA chondrule material and associated metal. The loss of evaporated material from the chondrules could explain the volatile element fractionations. Mechanisms for how these fractionations occurred are necessarily speculative, but two possibilities are briefly explored.
    01/2010; 40(7):943 - 965. DOI:10.1111/j.1945-5100.2005.tb00166.x
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