2001ApJ...550.1000K

With the Infrared Space Observatory, we conducted 3x3 pixel imaging photometry of 12 luminosity class III stars, which were previously presumed to have dust particles around them, at far-infrared wavelengths (60 and 90 µm). Eleven out of 12 targets show a peak of excess (above photosphere) far-infrared emission at the location of the star, implying that the dust particles are truly associated with stars. To estimate the size of the excess emission source, the flux ratio of center to boundary pixels of the 3x3 array was examined. The radius of the dust emission is found to be ∼3000 to ∼10,000 AU for a thin shell distribution and ∼5000 to ∼25,000 AU for a uniform distribution. We consider three models for the origin of the dust: disintegration of comets, sporadic dust ejection from the star, and emission from nearby interstellar cirrus. The data seem to rule out the first model (as far as the ``Kuiper belt-like'' particles are assumed to be large blackbody grains) but do not enable us to choose between the other two models.