  Barium stars are extrinsic Asymptotic Giant Branch (AGB) stars. They present
the s-enhancement characteristic for AGB and post-AGB stars, but are in an
earlier evolutionary stage (main sequence dwarfs, subgiants, red giants). They
are believed to form in binary systems, where a more massive companion evolved
faster, produced the s-elements during its AGB phase, polluted the present
barium star through stellar winds and became a white dwarf. The samples of
barium stars of Allen & Barbuy (2006) and of Smiljanic et al. (2007) are
analysed here. Spectra of both samples were obtained at high-resolution and
high S/N. We compare these observations with AGB nucleosynthesis models using
different initial masses and a spread of 13C-pocket efficiencies. Once a
consistent solution is found for the whole elemental distribution of
abundances, a proper dilution factor is applied. This dilution is explained by
the fact that the s-rich material transferred from the AGB to the nowadays
observed stars is mixed with the envelope of the accretor. We also analyse the
mass transfer process, and obtain the wind velocity for giants and subgiants
with known orbital period. We find evidence that thermohaline mixing is acting
inside main sequence dwarfs and we present a method for estimating its depth.
