Brightness temperature T_B in function of the wavelength for the nine sample stars between 5 μm and 7 cm. The full line indicates the brightness temperatures derived from the theoretical model, the asterisks show the brightness temperatures derived from the observations. A reversed triangle represents an upper limit. The error bars on the observational data take the uncertainty on the observations and on the angular diameter into account. The PACS and SPIRE wavelength ranges are indicated by a dotted line, to facilitate comparison to the wavelength region were a flux excess is seen.