Far-infrared observations of the peculiar variable star R Aquarii.

The first results on the peculiar Mira variable star R Aquarii obtained by the IRAS satellite in the far-infrared region are presented. A simple model in terms of circumstellar dust emission is given to interpret the far-infrared excess. A two-dust shell model with silicate grains of size 1 μm at temperatures 800±80K and 87±8K seems to fit the observations remarkably well in addition to the stellar emission at 2800K. It is shown that this model explains the near and mid-infrared fluxes as well. In comparison, another Mira variable U Ori also showed two dust shells but with lower temperatures and smaller grain sizes. Implications of these results on the nature of R Aquarii are discussed.