Letter to the Editor

High-resolution thermal infrared imaging of MWC300^*

VLT/VISIR observations in BURST mode

¹ Lab. H. Fizeau, CNRS UMR 6525, Univ. de Nice-Sophia Antipolis, Observatoire de la Côte d'Azur, 06108 Nice Cedex 2, France e-mail: Armando.Domiciano@unice.fr
² LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France

Received: 4 December 2007
Accepted: 24 January 2008

Abstract

Context.B[e] stars are expected to possess dusty circumstellar environments, which are responsible for a strong infrared (IR) excess.

Aims.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] MWC 300.

Methods.We obtained diffraction-limited images of MWC 300 at 11.25 μm using the BURST mode of the VLT/VISIR instrument.

Results.MWC 300 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 ± 10 mas. For a distance of 1.8 kpc, we obtain a linear size of 125±18 AU = (1.87±0.26) 10¹³ m 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 MWC 300 at 11.25 μm is estimated as 84.5±1.4 Jy = (20.0±0.3) 10^-13 W/m²/μm.

Conclusions.The VLT/VISIR now offers the possibility of obtaining mid-IR diffraction-limited images with a high signal-to-noise ratio. The MWC 300'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.