Polymorphism in Presolar Al 2 O 3 Grains from Asymptotic Giant Branch Stars
Abstract
We report microstructural and isotopic analyses of two presolar Al 2 O 3 grains. Aluminum oxide is important cosmically, because its presence has been detected in the infrared spectra of the circumstellar envelopes of O-rich asymptotic giant branch stars and because it is predicted to be the first solid to condense in these stellar environments. The two grain structures, one corundum and the other amorphous, confirm that asymptotic giant branch stars produce both phases. The variation in structure and Ti content demonstrates that Al 2 O 3 can condense in the absence of TiO 2 seed clusters but that Ti may be important in determining the crystal structure.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Sep 03, 2004
- Source ID
- 10.1126/science.1101099
Entities
People
- Conel M. O’d. Alexander
- Larry R. Nittler
- Rhonda Stroud
Organizations
- Carnegie Institution for Science
- United States Naval Research Laboratory