The synthesis of Ti44 and Ni56 in massive stars

Abstract

We discuss the influence of rotation on the combined synthesis of Ti44 and Ni56 in massive stars. While Ni56 is significantly produced by both the complete and incomplete explosive Si burning, Ti44 is mainly produced by the complete explosive Si burning, with a minor contribution (in standard non rotating models) from the incomplete explosive Si burning and the O burning (both explosive and hydrostatic). We find that, in most cases, the thickness of the region exposed to the incomplete explosive Si burning increases in rotating models (v_ini=300 km/s) and since Ni56 is significantly produced in this zone, the fraction of mass coming from the complete explosive Si burning zone, necessary to get the required amount of Ni56, reduces. Therefore the amount of Ti44 ejected for a given fixed amount of Ni56 decreases in rotating models. However, some rotating models at [Fe/H]=-1 develop a very extended O convective shell in which a consistent amount of Ti44 is formed, preserved and ejected in the interstellar medium. Hence a better modeling of the thermal instabilities (convection) in the advanced burning phases together with a critical analysis of the cross sections of the nuclear reactions operating in O burning are relevant for the understanding of the synthesis of Ti44.

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