Radiation from the central sources. Top: The spectral energy distributions. The crosses show the observations; the dotted curves show fittings; and the solid curves show those corrected for foreground extinction. Middle: Cumulative fraction of the integrations used in Eqs. (38), (40) and (45). The horizontal axis is the maximum wavelength for integration up to λ=15 μm. Bottom: Same as the middle panels but for the integrations used in Eq. (39).