THE α-PROCESS IN SUPERNOVA PRESOLAR SiC GRAINS

and Karl-Ludwig Kratz, Department of Physics, University of Notre Dame, Notre Dame, IN 46556, USA, Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem 91904, Israel ([email protected]), Max-PlanckInstitut für Chemie (Otto-Hahn-Institut), D-55128 Mainz, Germany Introduction The rare presolar SiC grains from supernovae (SNe), called SiC of type X, make up only ∼ 1% of all presiolar SiC grains [1]. Identifying SNe as their source stars is based on enrichments in C (for most grains), N and Si. In addition, a large fraction of the grains bears evidence for in-situ decay of the SN produced short-lived radioisotopes Al (t1/2 = 7.1 × 10 yr), Ti (t1/2 = 60 yr) and V (t1/2 = 331 d) [1]. Two recent studies measured the isotopic composition of heavy elements in SiC X grains: Pellin et al. [2] measured the isotopic composition of Fe, Sr, Zr, Mo, Ru, and Ba, and Marhas et al. [3] measured the isotopic composition of Ba. Surprisingly, none of the heavy elements measured showed the expected composition of the r-process. The Zr in 3 of the 4 measured grains was characterized by large enrichments in Zr, while Mo in 6 of the 8 measured grains had a peculiar large enrichment in Mo and Mo. The neutron burst model of Meyer et al. [4] explained these Zr and Mo compositions very well qualitatively [2], and as was shown by Marhas et al. [3], mixing of neutron burst end member and solar composition could account for the compositions of most of the grains. However, the Ba isotopic composition could not be explained by the neutron burst [3], as well as the Mo compsition of grain 153-8, which is solar within uncertainties for all isotopes, but depleted in Mo. Here we present preliminary results of the new High Entropy Wind (HEW) model for the nucleosynthetic α-process that can explain the Mo isotopic compositions of most grains, including that of grain 153-8. This is an alternative mechanism to the neutron burst model.