Aluminum-26 production from a stellar evolutionary sequence.

The nucleosynthesis occurring in the carbon shell of a massive star with a helium core mass of 12 solar masses is examined with emphasis on the production of Al-26. The conditions in the shell are taken directly from stellar evolutionary calculations and contain no adjusted parameters. The nucleosynthesis is characterized by incomplete burning of C-12 in a hydrostatic convective shell at high temperature (about 1.0 to 1.3 billion K). Only about 10% of the material in this shell is subjected to significant explosive nucleosynthesis following the passage of the supernova shock wave. The postshock conditions are calculated explicitly for conditions taken from the hydrodynamic models. The nuclei whose origins are normally ascribed to explosive carbon burning are produced in this evolution along with Al-26 at a level where the Al-26/Al-27 ratio is approximately 0.001 to 0.002. This production ratio is sufficient, in most models, to account for the magnesium anomalies detected in the Allende meteorite.