AN INVESTIGATION INTO THE ORIGIN OF Fe-RICH PRESOLAR SILICATES IN ACFER 094
Presolar silicate and oxide grains from primitive meteorites are recognized as 'stardust' on the basis of their extremely anomalous O isotopic compositions. We report data on 48 O-anomalous grains that were identified in grain size separates of the ungrouped carbonaceous chondrite Acfer 094. A majority of these grains exhibit high {sup 17}O/{sup 16}O isotopic ratios along with solar to sub-solar {sup 18}O/{sup 16}O ratios and may have originated in low-mass stars with close-to-solar metallicity. Four silicate grains that contain {sup 18}O enrichments were also measured for their Si isotopes. A comparison of their O and Si isotopic compositions with model predictions indicates that these {sup 18}O-rich grains may have formed in supernova ejecta. Four of the O-anomalous grains are oxides while the remaining 44 are silicates, based on elemental compositions determined by Auger spectroscopy. The presolar oxides include a TiO{sub 2} grain and a grain with spinel stoichiometry. The silicate grains largely exhibit ferromagnesian compositions, although a few grains also contain small amounts of Ca and/or Al. Stoichiometric silicates were further classified as either olivine-like or pyroxene-like, and in this study pyroxene-like grains are more abundant than olivine-like ones. The majority of silicates contain more Fe than Mg, including a few grains with Fe-rich end-member compositions. Spectroscopic observations indicate the presence of Mg-rich silicates in the atmospheres of stars and the interstellar medium. Mg-rich minerals such as forsterite and enstatite form by equilibrium condensation in stellar environments. However, non-equilibrium condensation can result in higher Fe contents and the occurrence of such processes in the outflows of stars may account for the Fe-rich grains. Alternatively, secondary processes may play a role in producing the Fe enrichments observed in the presolar silicate grains identified in the matrix of Acfer 094.
- OSTI ID:
- 21448807
- Journal Information:
- Astrophysical Journal, Vol. 714, Issue 2; Other Information: DOI: 10.1088/0004-637X/714/2/1624; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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COSMOLOGY AND ASTRONOMY
CHONDRITES
ENSTATITE
GRAIN SIZE
ISOTOPE RATIO
MATTER
OLIVINE
OXYGEN 16
OXYGEN 17
OXYGEN 18
SILICATES
SILICON ISOTOPES
SPECTROSCOPY
SPINELS
STELLAR ATMOSPHERES
STOICHIOMETRY
SUPERNOVAE
TITANIUM OXIDES
ATMOSPHERES
BINARY STARS
CHALCOGENIDES
DIMENSIONLESS NUMBERS
ERUPTIVE VARIABLE STARS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
ISOTOPES
LIGHT NUCLEI
METEORITES
MICROSTRUCTURE
MINERALS
NUCLEI
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
SILICATE MINERALS
SILICON COMPOUNDS
SIZE
STABLE ISOTOPES
STARS
STONE METEORITES
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
VARIABLE STARS