$s$-Processing in AGB Stars Revisited. II. Enhanced $^{13}$C Production Through MHD-Induced Mixing

Understand

Slow neutron captures are responsible for the production of about $50\%$ of elements heavier than iron, mainly, occurring during the asymptotic giant branch phase of low-mass stars ($1$ $\lesssim M$/M$_{\odot}$ $\lesssim$ $3$), where the main neutron source is the $^{13}$C($\alpha$,n)$^{16}$O reaction.

• This last is activated from locally-produced $^{13}$C, formed by partial mixing of hydrogen into the He-rich layers.
• We present here the first attempt at describing a physical mechanism for the formation of the $^{13}$C reservoir, studying the mass circulation induced by magnetic buoyancy and without adding new free parameters to those already involved in stellar modelling.
• Our approach represents the application, to the stellar layers relevant for $s$-processing, of recent exact, analytical 2D and 3D models for magneto-hydrodynamic processes at the base of convective envelopes in evolved stars in order to promote downflows of envelope material for mass conservation, during the occurrence of a dredge-up phenomenon.