Normalized flux contributions as a function of β for the ALMA observations. The red line shows the contributions derived from the cross-section model. The open symbols show the contributions of the β intervals for the best fit model when relaxing the assumption on the grain size distribution. The values that are below 2.5 × 10⁻² are considered as upper limits, and are represented by downward triangles. The horizontal bars show the width of the β intervals, and the vertical bars are the lσ confidence interval. The other solid lines show the contributions for models that account for the optical properties of the particles (see text for details).