SED slope between the 12 and 70 μm (α₁₂₋₇₀) as a function of the SED slope between the Ks-band and 12 μm (α_Ks − 12). Transitional disks from the literature meeting the selection criterion are marked as red dots, green downward arrows are those for which only upper limits could be estimated. Class II objects are black dots. Blue squares are pretransitional disks from Espaillat et al. (2011). There is a clear separation between Class II and transitional disks due to the different shape of their SED. The single black dot with α > 0 is ESO-Hα 559, an edge-on disk. This diagram shows the potential for transitional disk classification using the 70 μm band.