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The AKARI and Spitzer satellites provided an unique opportunity to observe avariety of stars, which are considered as departing from the Asymptotic GiantBranch (AGB) and have started their post-AGB evolution recently. Most of thesestars are absent optically and are bright in the mid-IR wavelength range.Spectra of close to 200 objects have been obtained. For all of them the 1-60micron spectral energy distribution has been constructed using photometric datafrom various surveys. We report here on the results of Spitzer observations of88 IRAS selected post-AGB candidates and discuss them in comparison to theresults of the AKARI observations of post-AGB candidates reported elsewhere inthese proceedings. The dust compositions can be divided broadly in oxygen- andcarbon-rich types, but a variety of intermediate types have been found. Amongthe oxygen-rich stars amorphous dust prevails, but a few sources show emissionfeatures from crystalline dust. The spectra from carbon-rich shells may becompletely featureless, may show emission features from PAHs or a molecularabsorption line from C2H2. We found also sources with a neon emission line at12.8 micron. More than a third of all sources show a near-infrared excess at <5 micron and almost all of them show evidence of C-rich dust in their shells.We postulate that the emerging post-AGB wind after the end of AGB evolutioncontains always carbon-rich dust irrespective of the chemistry of the formerAGB star.

The transition from AGB to post-AGB evolution as observed by AKARI and Spitzer