TRANSMISSION ELECTRON MICROSCOPY OF Al-RICH SILICATE STARDUST FROM ASYMPTOTIC GIANT BRANCH STARS
- Institute for Mineralogy, University of Muenster, Correnssstr. 24, D-48149 Muenster (Germany)
- Max Planck Institute for Chemistry, Particle Chemistry Department, Hahn-Meitner-Weg 1, D-55128 Mainz (Germany)
We report on transmission electron microscopy (TEM) investigations of two mineralogically unusual stardust silicates to constrain their circumstellar condensation conditions. Both grains were identified by high spatial resolution nano secondary ion mass spectrometry (NanoSIMS) in the Acfer 094 meteorite, one of the most pristine carbonaceous chondrites available for study. One grain is a highly crystalline, highly refractory (Fe content < 0.5 at%), structurally undisturbed orthopyroxene (MgSiO{sub 3}) with an unusually high Al content (1.8 {+-} 0.5 at%). This is the first TEM documentation of a single crystal pyroxene within the complete stardust silicate data set. We interpret the microstructure and chemistry of this grain as being a direct condensate from a gas of locally non-solar composition (i.e., with a higher-than-solar Al content and most likely also a lower-than-solar Mg/Si ratio) at (near)-equilibrium conditions. From the overabundance of crystalline olivine (six reported grains to date) compared to crystalline pyroxene (only documented as a single crystal in this work) we infer that formation of olivine over pyroxene is favored in circumstellar environments, in agreement with expectations from condensation theory and experiments. The second stardust silicate consists of an amorphous Ca-Si rich material which lacks any crystallinity based on TEM observations in which tiny (<20 nm) hibonite nanocrystallites are embedded. This complex assemblage therefore attests to the fast cooling and rapidly changing chemical environments under which dust grains in circumstellar shells form.
- OSTI ID:
- 22126597
- Journal Information:
- Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 769; ISSN ASJOAB; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
AN INVESTIGATION INTO THE ORIGIN OF Fe-RICH PRESOLAR SILICATES IN ACFER 094
The abundance of presolar grains in comet 81P/WILD 2
Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
79 ASTRONOMY AND ASTROPHYSICS
ASYMPTOTIC SOLUTIONS
CHONDRITES
CONDENSATES
COOLING
DUSTS
EQUILIBRIUM
MAGNESIUM SILICATES
MASS SPECTROSCOPY
METEOROIDS
MICROSTRUCTURE
MONOCRYSTALS
REFRACTORIES
SPATIAL RESOLUTION
STARS
TRANSMISSION ELECTRON MICROSCOPY