1998A&A...337..808M

We report on a first attempt to detect Vega's disk through optical scattered light by using linear photopolarimetry. Polarization measurements on the aureole of Vega were carried out between 7'' and 30'' from the star with a 10'' diameter hole and down to polarization level of ∼10^–4. No signal reliably attributable to circumstellar dust was detected, and an upper limit to the polarized surface brightness of the disk is derived. This upper limit for Vega's disk is about 200 times lower than the polarized brightness observed around β Pic, at an angular offset of 15'' from the stars. The upper limit is also compared to a simple model, in which one assumes a plausible total dust mass of 2x10^–8M_☉, and a pole-on oriented disk with a typical radius of ∼20'' as favoured by far-infrared and submillimetric experiments. We also suppose that the grains are spherical (Mie) particles. Our analysis can exclude that a major part of dust mass would consist of grains of 0.01-0.3µm, as in the interstellar medium. If a single size is assumed, the observational upper limit favours radii of at least 5-10µm or larger. If a size distribution including large particles (∼300µm) is assumed, the data suggests that only a very small fraction (∼1/1000 ) of the dust mass is in 0.01-0.3µm grains.