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| Paper: |
The Transition from AGB to Post-AGB Evolution as Observed by AKARI and Spitzer |
| Volume: |
418, AKARI, a Light to Illuminate the Misty Universe |
| Page: |
159 |
| Authors: |
Engels, D.; García-Lario, P.; Bunzel, F.; García-Hernández, D. A.; Perea-Calderón, J. V. |
| Abstract: |
The AKARI and Spitzer satellites provided an unique opportunity to observe a variety of stars, which are considered as departing from the Asymptotic Giant Branch (AGB) and have started their post-AGB evolution recently. Most of these stars 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 1–60 μm spectral energy distribution has been constructed using photometric data from various surveys. We report here on the results of Spitzer observations of 88 IRAS selected post-AGB candidates and discuss them in comparison to the results of the AKARI observations of post-AGB candidates reported elsewhere in these proceedings. The dust compositions can be divided broadly in oxygen- and carbon-rich types, but a variety of intermediate types have been found. Among the oxygen-rich stars amorphous dust prevails, but a few sources show emission features from crystalline dust. The spectra from carbon-rich shells may be completely featureless, may show emission features from PAHs or a molecular absorption line from C2H2. We found also sources with a neon emission line at 12.8 μm. More than a third of all sources show a near-infrared excess at λ < 5 μm 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 evolution contains always carbon-rich dust irrespective of the chemistry of the former AGB star. |
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