TRENDS IN 44Ti AND 56Ni FROM CORE-COLLAPSE SUPERNOVAE

We compare the yields of Ti-44 and Ni-56 produced from post-processing the thermodynamic trajectories from three different core-collapse models-a Cassiopeia A progenitor, a double shock hypernova progenitor, and a rotating two-dimensional explosion-with the yields from exponential and power-law trajectories. The peak temperatures and densities achieved in these core-collapse models span several of the distinct nucleosynthesis regions we identify, resulting in different trends in the Ti-44 and Ni-56 yields for different mass elements. The Ti-44 and Ni-56 mass fraction profiles from the exponential and power-law profiles generally explain the tendencies of the post-processed yields, depending on which regions are traversed by the model. We find that integrated yields of Ti-44 and Ni-56 from the exponential and power-law trajectories are generally within a factor two or less of the post-process yields. We also analyze the influence of specific nuclear reactions on the Ti-44 and Ni-56 abundance evolution. Reactions that affect all yields globally are the 3 alpha, p(e(-),nu(e))n and n(e(+), (nu(e)) over bar )p. The rest of the reactions are ranked according to their degree of impact on the synthesis of Ti-44. The primary ones include Ti-44(alpha, p)V-47, Ca-40(alpha, gamma)Ti-44, V-45(p, gamma)Cr-46, Ca-40(alpha, p)Sc-43, F-17(alpha, p)Ne-20, Na-21(alpha, p)Mg-24, Sc-41(p, gamma)Ti-42, Sc-43(p, gamma)Ti-44, Ti-44(p, gamma)V-45, and Ni-57(p, gamma)Cu-58, along with numerous weak reactions. Our analysis suggests that not all Ti-44 need to be produced in an alpha-rich freeze-out in core-collapse events, and that reaction rate equilibria in combination with timescale effects for the expansion profile may account for the paucity of Ti-44 observed in supernova remnants.