  We report mid-infrared observations of SGR 1806-20 and its environment - with
the highest spatial resolution in this domain to date - using ESO/VISIR in 2005
and 2006, and we retrieved Spitzer/IRAC-MIPS archival data of the same field.
  We aimed at studying the mid-infrared emission of the stars associated with
the same cluster as SGR 1806-20, to detect variations that could be due to the
high-energy activity of the magnetar through interaction with the dust. We also
aimed at studying the morphology of the cloud close to the centre of the
cluster.
  We performed broadband photometry of three stars - LBV 1806-20, a WC9 and an
O/B supergiant - on our VISIR images, as well as on the IRAC data. We then
built and fitted their broadband spectral energy distributions with a
combination of two absorbed black bodies, representing their stellar
components, as well as a possible mid-infrared excess, in order to derive their
physical parameters.
  We show that LBV 1806-20 and the WC9 star exhibit a mid-infrared excess,
likely because of the presence of circumstellar dust related to their winds. We
also show that only LBV 1806-20 had a variable flux over a period of two years,
variability which is due to its LBV nature rather than to a heating of the gas
and dust cloud by the high-energy emission of SGR 1806-20. Finally, differences
in the intrinsic absorptions of the three stars show an inhomogeneous structure
of the density of the gas and dust cloud in the massive star cluster.
