AKARI and Spitzer observations of heavily obscured C-rich AGB/post-AGB stars

TL;DR

This study uses AKARI and Spitzer infrared observations to analyze heavily obscured C-rich AGB and post-AGB stars, revealing their dust properties and evolutionary stage through spectral analysis.

Contribution

First detailed infrared spectral analysis of heavily obscured C-rich AGB/post-AGB stars using AKARI and Spitzer data, determining dust chemistry and evolutionary status.

Findings

Most sources are C-rich and extremely obscured.

Detected molecular absorptions like acetylene, indicating early post-AGB stage.

No PAH features observed in the spectra.

Abstract

We present AKARI/IRC and Spitzer/IRS observations of a selected sample of galactic IRAS sources considered to be heavily obscured AGB/post-AGB stars based on their characteristic IRAS colours. All of them are completely invisible in the optical range but extremely bright in the infrared. Based on AKARI and Spitzer spectroscopy and using DUSTY we are able to determine the dominant chemistry of their circumstellar shells as well as the properties of the dust grains contained in these shells. Most of the sources are found to be C-rich (being the reddest C-rich stars observed so far). We find only molecular absorptions (and no PAH features) such as acetylene (C2H2) at 13.7 micron, indicative of an early post-AGB stage. We shortly discuss our findings in the context of stellar evolution during the hidden "transition phase" from AGB stars to Planetary Nebulae.