2008A&A...480L..29D

B[e] stars are expected to possess dusty circumstellar environments, which are responsible for a strong infrared (IR) excess. Using single-dish diffraction-limited imaging in the thermal infrared domain, we aim at measuring the angular extension of the dusty environment of the galactic B[e] MWC300. We obtained diffraction-limited images of MWC300 at 11.25µm using the BURST mode of the VLT/VISIR instrument. MWC300 is partially, but statistically significantly, resolved by VISIR so that we could measure the size of its dusty envelope for the first time. By assuming a 2D circular Gaussian intensity distribution and using different image analysis methods we measured a FWHM angular size of 69±10mas. For a distance of 1.8 kpc, we obtain a linear size of 125±18AU=(1.87±0.26)x10¹³m for the circumstellar dust emitting in the mid-IR. This measured size is shown to agree with a model that was calculated with our radiative radiative transfer code and constrained by previously reported SED data. Additionally, the flux of MWC300 at 11.25µm is estimated as 84.5±1.4Jy=(20.0±0.3)x10^–13W/m²/µm. The VLT/VISIR now offers the possibility of obtaining mid-IR diffraction-limited images with a high signal-to-noise ratio. The MWC300's size as directly measured in this work is compatible with the theoretical size of a nearly edge-on dusty disc estimated in previous works. Interferometric data at milliarcsec angular resolution are required to reveal details on this dusty envelope.