A far-infrared survey of bow shocks and detached shells around AGB stars
  and red supergiants
  Far-infrared Herschel/PACS images at 70 and 160 micron of a sample of 78
Galactic evolved stars are used to study the (dust) emission structures,
originating from stellar wind-ISM interaction. In addition, two-fluid
hydrodynamical simulations of the coupled gas and dust in wind-ISM interactions
are used to compare with the observations.
  Four distinct classes of wind-ISM interaction (i.e. "fermata", "eyes",
"irregular", and "rings") are identified and basic parameters affecting the
morphology are discussed. We detect bow shocks for ~40% of the sample and
detached rings for ~20%. De-projected stand-off distances (R_0) -- defined as
the distance between the central star and the nearest point of the interaction
region -- of the detected bow shocks ("fermata" and "eyes") are derived from
the PACS images and compared to previous results, model predictions and the
simulations. All observed bow shocks have stand-off distances smaller than 1
pc. Observed and theoretical stand-off distances are used together to
independently derive the local ISM density.
  Both theoretical (analytical) models and hydrodynamical simulations give
stand-off distances for adopted stellar properties that are in good agreement
with the measured de-projected stand-off distance of wind-ISM bow shocks. The
possible detection of a bow shock -- for the distance limited sample -- appears
to be governed by its physical size as set roughly by the stand-off distance.
In particular the star's peculiar space velocity and the density of the ISM
appear decisive in detecting emission from bow shocks or detached rings.
Tentatively, the "eyes" class objects are associated to (visual) binaries,
while the "rings" generally appear not to occur for M-type stars, only for C or
S-type objects that have experienced a thermal pulse.
