The formation of the C-13 pocket in Asymptotic Giant Branch stars and related nucleosynthesis

摘要

We present new tests for the formation of the C-13 pocket in AGE stars. Using the Schwarzschild criterion for convection in the framework of the FRANEC stellar evolutionary code, the inclusion of an exponentially decaying velocity profile below the base of the convective envelope allows a small amount of protons to diffuse into the C- and He-rich intershell during the occurrence of the third dredge up. At H reignition, a consistent amount of C-13 (and N-14) is formed in the top layers of the He intershell. The C-13 pocket extends over regions where the abundance of N-14 is small. In the interpulse period, all C-13 nuclei are consumed by the C-13(alpha ,n)O-16 reaction, providing an efficient source for the s-process nucleosynthesis. The penetration of the envelope convection into the He- and C-rich layers during the third dredge up is extremely sensitive to the dumping parameter that describes the efficiency of the velocity profile. Note that such parameter cannot be derived (at present) from numerical simulations of stellar convection. [References: 14]