Imaging the circumstellar dust distribution around AGB stars

TL;DR

This study uses polarized light imaging with the PolCor instrument to map dust distributions around AGB stars, revealing asymmetries and detached shells that inform understanding of stellar evolution into planetary nebulae.

Contribution

First high-resolution polarized imaging of dust around multiple AGB stars, revealing asymmetries and detached shells with implications for stellar evolution.

Findings

Bi-polar dust distribution around W Aql

Detection of detached shells in DR Ser and U Cam

Insights into mass-loss symmetry and evolution

Abstract

Stellar light from an AGB star is scattered by the circumstellar dust and polarized in the direction perpendicular to the source. Therefore, images of circumstellar envelopes around AGB stars in polarized light traces the dust distribution and can be used to search for asymmetries, and to achieve a better understanding of the mechanisms at play when AGB stars are transformed into planetary nebulae. The PolCor instrument is a combined imager, polarimeter, and coronograph providing images with an angular resolution down to 0.2". We have used it to map the dust distribution around three AGB stars: W Aql, and the detached shell sources DR Ser, and U Cam. W Aql is a binary and we find indications of a bi-polar dust distribution around the star. The observations of the latter two sources clearly reveal the detached shells, likely the result of a brief, strongly enhanced mass-loss rate during the late evolution of these stars. Mapping the detached shells gives us clues to the symmetry of the mass loss and important evolutionary processes.