Data analysis for L260. Warm Spitzer IRAC surface brightness maps (off-subtracted) at 3.6 and 4.5 μm (panels A), B)) and cold Spitzer map at 8 μm (panel C) in a 5.5′ × 5.5′ region around the core. The white square indicates the 1.1′ × 1.1′-region where surface brightness ratios have been measured. The optical depth for extinction of external radiation passing through the core and to the observer (directionally averaged) for a core with the overall properties of L260 is shown in panels D) and E) (3.6 and 4.5 μm). Panel F): horizontal (thick) and vertical (thin) cuts through the central 200 pixel in the two bands (black for 3.6 μm and green for 4.5 μm). Panel G): map of the ratio of the off-subtracted surface brightnesses R at 3.6 and 4.5 μm. Panel H) shows the R pixel number distribution within the white square (pixels affected by point sources or by the column-pulldown effect have been masked). Panel I): R_theo as a function of the maximum grain size a₂ (thick black), with the notation from Fig. 4. The observational R-distribution from panel H) is plotted and color-coded, and both the maximum value and the two half-maximum values are plotted as dashed lines. The horizontal black bar indicates the a₂ agreement range of R_theo and R_obs.