s Processing in post-AGB and CH stars at low metallicity

New computations of s processing in the Thermally Pulsing Asymptotic Giant Branch (TP-AGB) phases of Low Mass Stars (LMS) at different metallicities a re presented. The results are compared with the observed abundances of elem ents heavier than Fe in post-AGB supergiants and in CH stars (both giants a nd subgiants), which are the result of mass transfer episodes from AGE comp anions. Our models explain the observed integrated abundances of heavy and light s elements ('hs' and 'ls', respectively) down to very low metalliciti es ([Fe/H] = -3), indicating that an intrinsic dispersion in the neutron ca pture efficiency exists at any epoch. We also succeed in reproducing the de tailed photospheric composition in s elements in the stars where this is av ailable.