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Paper: Imaging the Circumstellar Dust Distribution around AGB Stars with the NOT/PolCor Instrument
Volume: 445, Why Galaxies Care about AGB Stars II: Shining Examples and Common Inhabitants
Page: 367
Authors: Ramstedt, S.; Maercker, M.; Olofsson, G.; Olofsson, H.; Schöier, F. L.
Abstract: Stellar light from an AGB star is scattered by circumstellar dust and polarized in the direction perpendicular to the source. Therefore, images of circumstellar envelopes around AGB stars in polarized light trace 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: the S star W Aql, and the detached shell carbon stars 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.
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