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0242598024
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note
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These grains are identified as "circumstellar" or equivalently "stardust," because their O isotopic compositions establish their origins as stellar ejecta. These grains must also have traversed the interstellar medium before their incorporation into the nascent solar nebula, and could also be considered "interstellar dust."
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11
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0242513288
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note
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GEMS grains are a major component of cometary/anhydrous IDPs, occasionally exceeding 50 weight % of the IDP mass. They are typically 01 to 0.5 μm in size, have approximately chondritic elemental abundances (with the exception of C), and have optical properties consistent with those observed for interstellar amorphous silicates (13). GEMS have also been observed within isotopically anomalous (H and N) organic matter thought to be of presolar origin (12).
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12
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39449086671
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0242429892
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note
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- peak was less than 1%o, with a mass-resolving power of at least 9000 (Cameca definition), or ∼6000 in the conventional definition. Image acquisition times ranged from 3 to 10 hours, consuming 30 to 100 nm of surface material. The magnetic field was controlled with a nuclear magnetic resonance probe, which kept peak positions stable to ΔM/M < 5 ppm. Thin sections were coated with 50 Å of Au or C to avoid sample charging.
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20
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0242681840
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note
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The IDP L2036 C4 was extracted from the ion probe mount by carving a section of the Au substrate measuring 200 x 200 μm by hand with a scalpel. The extracted section was glued to a flattened epoxy bullet with a cyanoacrylate adhesive. The Au was trimmed with a glass knife on an ultramicrotome, leaving a 30-μm plateau containing the IDP. The IDP was then embedded in resin, and after curing several days was sliced with a diamond knife into 50-nm sections. The sections were transferred to a 1-mm-aperture grid coated with Formvar. After TEM analysis, the entire mount (Formvar with seven sections) was transferred to a preformed Au plateau, where the sections were subsequently imaged in the NanoSIMS.
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21
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0242429888
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note
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The data were analyzed with custom software written in the Interactive Data Language. In most cases, a range of image layers (5 to 10) was selected, discarding the first low-intensity images and the final images, which for the TEM sections were often compromised by rapid erosion of the epoxy or carbon substrate. Candidate grains were manually defined and semiautomatically redefined in subsequent layers, with the particle positions and outlines being checked in each image layer.
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23
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0242513285
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note
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18O = 498.7). The standard deviations of the isotopic compositions of these "standard subgrains" were taken into account in the determination of the final measurement uncertainty. Final isotopic ratios and uncertainties were determined according to standard procedures. Grains that have O isotopic compositions that deviate from solar compositions by at least 3σ are identified as stardust.
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24
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21744457528
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27
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0242681839
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note
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We used a JEOL 2000FX TEM equipped with an Oxford instruments energy-dispersive x-ray (EDX) spectrometer to analyze ultramicrotome thin sections of the IDPs. The mineralogy and composition of grains >200 nm in diameter were determined with a combination of electron diffraction and quantitative EDX analysis and dark-field imaging.
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28
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0242513287
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note
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standard - 1) × 1000.
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29
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0242681838
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note
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18O < 20%o), 49 have solar O isotopic ratios within 2σ, and one is a circumstellar grain. We achieved the highest precision isotopic measurements on ultramicrotome thin sections deposited onto Au substrates. This mounting technique offers very flat conducting samples. Images acquired from TEM grid sections were limited by the sputtering lifetime of the epoxy and were compromised by stretching and tearing of holes in the epoxy and C substrate during the measurements.
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31
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0003347213
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Disks, and Regoliths, M. L. Sitko, A. L. Sprague, D. V. Lynch, Eds. (Astronomical Society of the Pacific, San Francisco, CA)
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37
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0242681836
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note
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Although the nanodiamonds are abundant in meteorites (up to 1000 ppm), it is possible that only a small fraction are presolar in origin, because the bulk C isotopic composition is solar and the anomalous Xe and N have low abundances.
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0242429885
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in preparation
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É. Zinner et al., in preparation.
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Zinner, É.1
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45
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0242598020
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note
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Supported by NASA grants NAGS-9801 and RTOP 344-31-40-07. This work was enabled by the revolutionary NanoSIMS ion microprobe, which was designed by G. Slodzian at the University of Orsay, Paris.
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