Influence of the total disk mass on the re-emitted flux of an unperturbed circumstellar disk. A comparison between a linear model (dotted line) that is useful for very low mass disks, a model on the basis of the Rayleigh-Jeans-law (solid line), and the flux simulated in the radiative transfer (dashed line) is shown. Every disk has an inner radius of R_in = 38 AU and an outer radius of R_out = 171 AU, and the hosting star is a G type star (Sect. 3). The disk consists of large dust grains.