For a sample of RS CVn binaries Busso and collaborators (Busso et al., 1987, 1988; Busso and Scaltriti, 1990) compared the observed energy distribution from the UV to the near-IR (and to IRAS bandpasses for some objects) with those calculated from the known radii and spectral types of the stellar components. About 25% of the sample gave evidence of an IR excess up to 0.7 mag, generally starting from the I-band. The excess is significantly larger than observational error. These same authors ascribe the excess to a thin dust shell surrounding the binary. Using the “dirty silicates” model by Jones and Merrill (1976) they find for the shell a temperature range of 1500 K to 2000 K, an optical depth of about 0.01 at 10 micrometers in the shell, and a distance of the shell from the stars to be typically about 100 times the radius of the larger star.
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