(Top) Relation between τ₂₅₀ and τ_J. The line length shows the τ_J range used in the total least squares fitting. The slopes (k) of the fits are indicated on the plot with the same colour as the fitted line. The ranges used are 0–2.5 (black), 0.25–2.5 (red), 0.5–2.5 (blue), 0.5–1 (green), and 1–2.5 (cyan). (Middle) Relation between τ₂₅₀ (with resolution 40″) and τ_J of individual stars, using a limit Δτ_J < 0.95. (Bottom) Relation between τ₂₅₀ and τ_J. The data of each region are fitted separately. The slope k and the mean error bars are indicated on the plots. The colour scales in the top and bottom panels correspond to the logarithmic density of points.