SIMBAD references

We have re-analysed the IRAS pointed observations of Vega. We find that the 60 µm emission of Vega is as extended as 35 ± 5 arcsec. This is much larger than the generally accepted 23 arcsec (Aumann et al. 1984). Adopting a distance for Vega of 8.1 pc, the IR emission must be originating from a dust shell with a radius of 140 AU. This implies that a significant fraction of the dust grains is larger than 0.1 µm, but smaller than 10 µm. Thus, to explain the 60 µm emission of Vega the presence of grains larger than 10 µm is not necessary. However, as the smallest grains (a < 10 µm) are blown away due to the radiation pressure, and the remaining small grains (a < 1 mm) have spiralled into the star due to the Poynting-Robertson effect, a continuous production of small grains must be going on.