Dust shell models for infrared sources

Recent reviews have demonstrated that a wide ranging selection of objects emit a major proportion of their energy at wavelengths longer than 1 µ m, including such intrinsically different objects as late type stars, Be stars, F supergiants and novae. In the majority of cases the infrared radiation has been interpreted in terms of thermal radiation from a circumstellar shell of solid 'dust' particles. Any attempt at a detailed comparison of theoretical energy distributions with observed infrared photometry encounters the problems of uncertainties in the absolute calibration, and limited accuracy of the observations.