|
Microstructure of a presolar hibonite
grain
Stroud R. M., Nittler L. R., Alexander C. M. O'D.,
Stadermann F. J., and Zinner E. K. (2005) Meteorit.
Planet. Sci. 40, A148.
ABSTRACT
Thermodynamic equilibrium calculations of dust
condensation in oxygen-rich stellar outflows predict that
corundum (Al2O3) is the first phase to
condense, followed by hibonite
(CaAl12O19). Microstructural studies
of presolar grains provide the possibility to test these
predictions, and help constrain circumstellar condensation
conditions. For Al2O3, the available
structural data from two grains support the thermodynamic
models, but no data from CaAl12O19
grains have been available. Comparison of the range of
oxygen isotope values of the approximately 20 known presolar
CaAl12O19 grains to those of the
several hundred Al2O3 grains indicates
that the two grain populations sample similar stellar source
populations, and thus likely similar circumstellar
condensation conditions. We report herein the first
structural data from a presolar
CaAl12O19 grain and confirm the
structural phase identification as hibonite.
|