NanoSIMS STUDIES OF SMALL PRESOLAR SiC GRAINS: NEW INSIGHTS INTO SUPERNOVA NUCLEOSYNTHESIS, CHEMISTRY, AND DUST FORMATION
- Max Planck Institute for Chemistry, Particle Chemistry Department, P.O. Box 3060, 55020 Mainz (Germany)
- Department of Physics and Astronomy, Clemson University, Clemson, SC 29634-0978 (United States)
- Washington University, Laboratory for Space Sciences and the Physics Department, One Brookings Drive, St. Louis, MO 63130 (United States)
We have studied more than 2000 presolar silicon carbide (SiC) grains from the Murchison CM2 chondrite in the size range 0.2-0.5 {mu}m for C- and Si-isotopic compositions. In a subset of these grains, we also measured N-, Mg-Al-, S-, and Ca-Ti-isotopic compositions as well as trace element concentrations. The overall picture emerging from the isotope data is quite comparable with that of larger grains, except for the abundances of grains from Type II supernovae (SNeII) and low-metallicity asymptotic giant branch (AGB) stars. Especially, the latter are much more abundant among submicrometer-sized grains than among micrometer-sized grains. This implies that SiC grains from lower-than-solar-metallicity AGB stars are on average smaller than those from solar metallicity AGB stars which provided the majority of presolar SiC grains. We identified five grains with large enrichments in {sup 29}Si (up to 3.5x solar) and {sup 30}Si (up to 3.9x solar in three of these grains). These grains are most likely from SNeII. The isotopically light S ({sup 32}S/{sup 34}S of 2x solar) together with the heavy Si in one of these grains suggests that molecule formation precedes macroscopic mixing and dust formation in SNII ejecta. This adds to the complexity of SN mixing calculations and should be considered in future studies. In total, about 2% of the presolar SiC grains in the size range 0.2-0.5 {mu}m appear to come from SNeII. This is about a factor of 2 higher than for micrometer-sized grains and suggests that SNeII, on average, produce smaller SiC grains than solar metallicity AGB stars. The high {sup 29}Si/{sup 30}Si ratio in one of the SN grains suggests that current SN models underestimate the {sup 29}Si production in the C- and Ne-burning regions by about a factor of 2. It is shown that with this adjustment the solar {sup 29}Si/{sup 28}Si ratio can be well reproduced in Galactic chemical evolution models and that a merger of our Galaxy with a low-metallicity satellite some 1.5 Gyr before solar system formation could account for the slope 1.3 of the Si mainstream line.
- OSTI ID:
- 21457095
- Journal Information:
- Astrophysical Journal, Vol. 719, Issue 2; Other Information: DOI: 10.1088/0004-637X/719/2/1370; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
ABUNDANCE
CHONDRITES
DUSTS
GALACTIC EVOLUTION
GALAXIES
INTERSTELLAR GRAINS
ISOTOPE RATIO
NUCLEAR REACTIONS
NUCLEOSYNTHESIS
SILICON 28
SILICON 29
SILICON 30
SILICON CARBIDES
SOLAR SYSTEM
SUPERNOVAE
BINARY STARS
CARBIDES
CARBON COMPOUNDS
DIMENSIONLESS NUMBERS
ERUPTIVE VARIABLE STARS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
EVOLUTION
ISOTOPES
LIGHT NUCLEI
METEORITES
NUCLEI
PARTICLES
SILICON COMPOUNDS
SILICON ISOTOPES
STABLE ISOTOPES
STARS
STONE METEORITES
SYNTHESIS
VARIABLE STARS