A transmission electron microscopy study of presolar hibonite

Abstract

We report isotopic and microstructural data on five presolar hibonite grains identified in an acid residue of the Krymka LL3.1 ordinary chondrite. Isotopic measurements by secondary ion mass spectrometry (SIMS) verified a presolar circumstellar origin for the grains. Transmission electron microscopy (TEM) examination of the crystal structure and chemistry of the grains was enabled by in situ sectioning and lift-out with a focused-ion-beam scanning-electron microscope. Comparisons of isotopic compositions with models indicate that four of the five grains formed in low-mass stars that evolved through the red-giant/asymptotic-giant branches, whereas one grain formed in the ejecta of a Type II supernova. Selected-area electron-diffraction patterns show that all grains are single crystals of hibonite. Some grains contain stacking faults and small spreads in orientation that can be attributed to a combination of growth defects and mechanical processing by grain-grain collisions. The similar structure of the supernova grain to those from RGB/AGB stars indicates a similarity in the formation conditions. Radiation damage, if present, occurs below our detection limit. Of the five grains we studied, only one has the pure hibonite composition of CaAl12O19. All others contain minor amounts of Mg, Si, Ti, and Fe. The microstructural data are generally consistent with theoretical predictions, which constrain the circumstellar condensation temperature to a range of 1480 K to 1743 K, assuming a corresponding total gas pressure between 1 x 10-3 and 1 x 10-6 atm. The TEM data were used to develop a calibration for SIMS determination of Ti contents in oxide grains. Grains with extreme 18O depletions, indicating deep mixing has occurred in their parent AGB stars, are slightly Ti-enriched compared to grains from stars without deep mixing, most likely reflecting differences in grain condensation conditions.

References in corpus (5)

• Aluminum-, Calcium- And Titanium-Rich Oxide Stardust In Ordinary Chondrite Meteorites
• Can Extra Mixing in RGB and AGB Stars Be Attributed to Magnetic Mechanisms?
• Coordinated Analyses of Presolar Grains in the Allan Hills 77307 and Queen Elizabeth Range 99177 Meteorites
• Magnetic Mixing in Red Giant and Asymptotic Giant Branch Stars
• Automated NanoSIMS Measurements of Spinel Stardust from the Murray Meteorite

Cited by in corpus (3)

• High Abundances of Presolar Grains and ${}^{15}$N-rich Organic Matter in CO3.0 Chondrite Dominion Range 08006
• High-temperature Dust Condensation around an AGB Star: Evidence from a Highly Pristine Presolar Corundum
• TEM analyses of in situ presolar grains from unequilibrated ordinary chondrite LL3.0 Semarkona