  We analyze a set of published elemental abundances from a sample of CH stars
which are based on high resolution spectral analysis of ELODIE and SUBARU/HDS
spectra. All the elemental abundances were derived from local thermodynamic
equilibrium analysis usingmodel atmospheres, and thus, they represent the
largest homogeneous abundance data available for CH stars up to date. For this
reason, we can use the set to constrain the physics and the nucleosynthesis
occurring in low mass AGB stars. CH stars have been polluted in the past from
an already extinct AGB companion and thus show s-process enriched surfaces. We
discuss the effects induced on the surface AGB s-process distributions by
different prescriptions for convection and rotation. Our reference theoretical
FRUITY set fits only part of the observations. Moreover, the s-process
observational spread for a fixed metallicity cannot be reproduced. At Fe/H]>-1,
a good fit is found when rotation and a different treatment of the inner border
of the convective envelope are simultaneously taken into account. In order to
increase the statistics at low metallicities, we include in our analysis a
selected number of CEMP stars and, therefore, we compute additional AGB models
down to [Fe/H]=-2.85. Our theoretical models are unable to attain the large
[hs/ls] ratios characterizing the surfaces of those objects. We speculate on
the reasons for such a discrepancy, discussing the possibility that the
observed distribution is a result of a proton mixing episode leading to a very
high neutron density (the so-called i-process)
