AKARI/IRC observations of heavily obscured oxygen-rich AGB and post-AGB stars

TL;DR

This study uses AKARI/IRC observations to analyze heavily obscured oxygen-rich AGB and post-AGB stars, revealing differences in dust composition and spectral features between the two types.

Contribution

It provides the first detailed spectral energy distribution modeling of heavily obscured oxygen-rich AGB and post-AGB stars using AKARI data, highlighting dust composition variations.

Findings

OH/IR stars show strong silicate absorption features.

Post-AGB stars have redder continua with weaker silicate absorption.

Modeling indicates different dust compositions in AGB and post-AGB stars.

Abstract

We present AKARI/IRC observations of a sample of six extremely red IRAS sources, of which three are variable OH/IR stars and the rest are early post-AGB stars. The OH/IR stars show a red continuum with the expected strong 10 micron silicate absorption feature, while the post-AGB stars show an even redder continuum accompanied with a comparably weak silicate absorption. We modelled the spectral energy distributions with DUSTY. While for the OH/IR stars a reasonable fit can be obtained with almost pure silicate dust, the post-AGB stars require a mixture of silicate and carbon-rich dust. We assume that in the latter objects the inner dust shell is carbon-rich, while the outer shells are still oxygen-rich.