Nuclear evolution as a function of temperature during expansion and cooling. Left: evolution of the mass fractions of ⁵⁵Co (solid lines), ⁵²Fe (dashed lines), and α (dot-dashed lines), for six different sets of parameters, as given in Table 3. The dotted lines show the quantity f, defined in Eq. (16). Right: evolution of the molar fluxes of the main reactions contributing to the abundance of ⁵⁵Co for the same set of parameters as in Fig. 2. Reactions building ⁵⁵Co are drawn as solid lines, reactions destroying it are drawn as dashed lines, and the absolute value of the net rate of dY(⁵⁵Co)/dt is drawn as a dotted line. Upper curves are for the reactions ⁵⁴Fe + p ⇆ ⁵⁵Co + γ, in which both line types are nearly indistinguishable. The middle curves are for the reactions ⁵⁶Ni + γ ⇆ ⁵⁵Co + p. Finally, the bottom curves are for the reactions ⁵⁵Fe + p ⇆ ⁵⁵Co + n.