  The aim of this paper is to investigate how the new imaging Polarimeter and
Coronograph (PolCor) at the Nordic Optical Telescope (NOT) can be used in the
study of circumstellar structures around AGB stars, with the purpose of
preparing for a study of a larger sample. We have observed two types of AGB
stars using the PolCor instrument on the NOT: the binary S-type star W Aql and
two carbon stars with detached shells, U Cam and DR Ser. The polarized light
traces the dust distribution around the stars. From the polarimeter images the
polarized intensity, the polarization degree, and the polarization angle over
the images are calculated. The location and extent of dust structures are
examined in the images. The total dust mass and the dust-to-gas ratios of the
detached shells are also calculated. The images of the circumstellar envelope
of W Aql show what seems to be an elongated structure in the south-west
direction. The detached shells of U Cam and DR Ser are clearly seen in the
images. This is the first time the detached shell around DR Ser has been
imaged. The radii and widths of the shells are determined and found to be 7.9"
and 7.6", and 0.9" and 1.2", for U Cam and DR Ser, respectively. This is
consistent with previous results. The dust masses of the feature south-west of
W Aql, and in the shells of U Cam and DR Ser are also estimated and found to be
1x10^-6, 5x10^-7, and 2x10^-6 Msun, respectively. W Aql is a known binary and
the shape of the circumstellar envelope seems to be in line with what could be
expected from binary interaction on these scales. For the shells, the results
are in agreement with previous investigations. Ages and formation time-scales
are also estimated for the detached shells and found to be consistent with the
thermal-pulse-formation scenario.
