Simplified disk geometry with a surface layer and the disk interior. The panels a–d explain the four emission components we discuss in Sect. 3.2.2–3.2.5, respectively. The green arrows indicate scattering of the stellar light at the wavelength of the observations. The blue arrows indicate the stellar light responsible for heating the surface layer and the disk interior. The red arrows indicate thermal emission from the surface layer and the disk interior. In the top panel, β is the radial grazing angle of the disk surface with respect to the incident light from the central illuminating source; δ is the radial inclination angle of the disk surface with respect to the midplane; and θ is the scattering angle.