Trends in ⁴⁴Ti and ⁵⁶Ni from core-collapse supernovae

We compare the yields of ⁴⁴Ti and ⁵⁶Ni 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 ⁴⁴Ti and ⁵⁶Ni yields for different mass elements. The ⁴⁴Ti and ⁵⁶Ni 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 ⁴⁴Ti and ⁵⁶Ni 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 ⁴⁴Ti and ⁵⁶Ni abundance evolution. Reactions that affect all yields globally are the 3α, p(e^-, υ_e)n and n(e⁺, υ_e)p. The rest of the reactions are ranked according to their degree of impact on the synthesis of ⁴⁴Ti. The primary ones include ⁴⁴Ti(α, p) ⁴⁷V, ⁴⁰Ca(α, γ)⁴⁴Ti, ⁴⁵V(p, γ)⁴⁶Cr, ⁴⁰Ca(α, p) ⁴³Sc, ¹⁷F(α, p)²⁰Ne, ²¹Na(α, p)²⁴Mg, ⁴¹Sc(p, γ) ⁴²Ti, ⁴³Sc(p, γ)⁴⁴Ti, ⁴⁴Ti(p, γ)⁴⁵V, and ⁵⁷Ni(p, γ)⁵⁸Cu, along with numerous weak reactions. Our analysis suggests that not all ⁴⁴Ti need to be produced in an α-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 ⁴⁴Ti observed in supernova remnants.