Probing S-Process Yields of Field Carbon Stars by the Analysis of 21micron Post-AGB Stars

The observational data guiding the theoretical chemical evolutionary models of AGB stars come mainly from the analysis of intrinsic and extrinsic s-process enriched objects. The first are the stars of the M-MS-S-SC-C star sequence which is thought to reflect, at least partly, the evolution on the AGB of a single star towards an increasing C/O ratio. The second are all binaries with excess abundances acquired by mass-transfer from the companion which is now a white dwarf. In this contribution we present a homogeneous abundance analysis of 21micron objects, which are carbon-rich probably single post-AGB stars. With their F to G spectral types a wide variety of chemical species can be studied quantitatively by using photospheric atomic lines. These objects are among the most s-process enriched objects known so far. We focus on the s-process distribution and the related neutron irradiation and compare the results with the enrichments observed in both intrinsic and extrinsic objects.