The Transition from AGB to Post-AGB Evolution as Observed by AKARI and Spitzer

Engels, D.; García-Lario, P.; Bunzel, F.; García-Hernández, D. A.; Perea-Calderón, J. V.
Referencia bibliográfica

AKARI, a Light to Illuminate the Misty Universe ASP Conference Series, Vol. 418, proceedings of a conference held 16-19 February 2009 at the University of Tokyo, Tokyo, Japan. Edited by Takashi Onaka, Glenn J. White, Takao Nakagawa, and Issei Yamamura. San Francisco: Astronomical Society of the Pacific, 2009, p.159

Fecha de publicación:
12
2009
Número de autores
5
Número de autores del IAC
0
Número de citas
1
Número de citas referidas
1
Descripción
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.