Production of Carbon-rich Presolar Grains from Massive Stars
Abstract
About a year after core-collapse supernova, dust starts to condense in the ejecta. In meteorites, a fraction of C-rich presolar grains (e.g., silicon carbide (SiC) grains of Type-X and low density graphites) are identified as relics of these events, according to the anomalous isotopic abundances. Several features of these abundances remain unexplained and challenge the understanding of core-collapse supernovae explosions and nucleosynthesis. We show, for the first time, that most of the measured C-rich grain abundances can be accounted for in the C-rich material from explosive He burning in core-collapse supernovae with high shock velocities and consequent high temperatures. The inefficiency of the 12C(α, γ)16O reaction relative to the rest of the α-capture chain at T > 3.5 × 108 K causes the deepest He-shell material to be carbon-rich and silicon-rich, and depleted in oxygen. The isotopic ratio predictions in part of this material, defined here as the C/Si zone, are in agreement with the grain data. The high-temperature explosive conditions that our models reach at the bottom of the He shell can also be representative of the nucleosynthesis in hypernovae or in the high-temperature tail of a distribution of conditions in asymmetric supernovae. Finally, our predictions are consistent with the observation of large 44Ca/40Ca observed in the grains. This is due to the production of 44Ti together with 40Ca in the C/Si zone and/or to the strong depletion of 40Ca by neutron captures.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 2013
- DOI:
- 10.1088/2041-8205/767/2/L22
- arXiv:
- arXiv:1303.3374
- Bibcode:
- 2013ApJ...767L..22P
- Keywords:
-
- stars: abundances;
- stars: evolution;
- stars: interiors;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 13 pages, 4 figures, The Astrophysical Journal Letters, accepted