Dust in AGB wind-ISM interaction regions
  We aim to constrain the dust mass and grain sizes in the interaction regions
between the stellar winds and the ISM around asymptotic giant branch stars. By
describing the dust in these regions, we aim to shed light on the role of low
mass evolved stars in the origin of dust in galaxies. We use images in the
far-infrared at 70 micron and 160 micron to derive dust temperatures and dust
masses in the wind-ISM interaction regions around a sample of carbon-rich and
oxygen-rich asymptotic giant branch (AGB) stars. The dust temperature and mass
are determined in two ways. First directly from the data using the ratio of the
measured fluxes and assuming opacities for dust with a constant grain size of
0.1 micron. We then perform 3D dust-radiative transfer models spatially
constrained by the observations to consistently calculate the temperature and
mass. For the radiative transfer models each model contains one constant grain
size, which is varied between 0.01 micron to 5.0 micron. We find that the
observed dust mass in the wind-ISM interaction regions is consistent with mass
accumulated from the stellar winds. For the carbon-rich sources adding the
spatial constraints in the radiative transfer models results in preferentially
larger grain sizes (approx. 2 micron). For the oxygen-rich sources the spatial
constraints result in too high temperatures in the models, making it impossible
to fit the observed far-infrared ratio irrespective of the grain size used,
indicating a more complex interplay of grain properties and the stellar
radiation field. The results have implications for how likely it is for the
grains to survive the transition into the ISM, and the properties of dust
particles that later act as seeds for grain growth in the ISM. However, the
results for the oxygen-rich sources show that the derivation of dust properties
is not straight forward, requiring more complex modelling
