Partial mixing and formation of the 13C pocket by internal gravity waves in asymptotic giant branch stars

We show that mixing by weak turbulence induced by internal gravity waves generated by turbulent gas motions near the base of the convective envelope presents a good alternative to convective overshooting and rotation-driven instabilities as a mechanism for partial mixing in thermally pulsing asymptotic giant branch (AGB) stars. Such mixing ingests protons into the He/C-rich zone which leads to formation of the C-13 pocket, a necessary ingredient of the current theory of the s-process under radiative conditions in low-mass AGB stars. We demonstrate that with appropriately chosen, physically reasonable parameters partial mixing by internal gravity waves may produce a much wider C-13 pocket than convective overshooting limited to an extent compatible with observations.