Halo contribution (left) and half-flux radius (right) of the best-fit ring model in the K band as afunction of the luminosity of the central star. The color codes the amount of halo contribution and the numbers refer to Table 2. On the right plot, the sublimation radius is computed for a grain sublimation temperature between 1500 K and 2000 K (shaded area). Different grain population models as computed in Pinte et al. (2008) are reported: Model A (amorphous silicate grains smaller than 1 μm) at 1500 K (dashed line) and 2000 K (solid line), and Model D (amorphous silicate and carbon grains smaller than 1 mm; dash-dotted line). All of these models include the scattered light processing.