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We report mid-infrared observations of SGR 1806-20 and its environment - withthe highest spatial resolution in this domain to date - using ESO/VISIR in 2005and 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 withthe same cluster as SGR 1806-20, to detect variations that could be due to thehigh-energy activity of the magnetar through interaction with the dust. We alsoaimed at studying the morphology of the cloud close to the centre of thecluster.  We performed broadband photometry of three stars - LBV 1806-20, a WC9 and anO/B supergiant - on our VISIR images, as well as on the IRAC data. We thenbuilt and fitted their broadband spectral energy distributions with acombination of two absorbed black bodies, representing their stellarcomponents, as well as a possible mid-infrared excess, in order to derive theirphysical 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. Wealso 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 gasand dust cloud by the high-energy emission of SGR 1806-20. Finally, differencesin the intrinsic absorptions of the three stars show an inhomogeneous structureof the density of the gas and dust cloud in the massive star cluster.

Mid-infrared VISIR and Spitzer observations of the surroundings of the magnetar SGR 1806-20