Abstract
presence of dust grains in the circumstellar envelopes of many stars is known primarily from their effect on infrared energy distributions. The early development of wideband photometry in the infrared was motivated by a desire to improve the effective temperature scale for cool stars and to study the interstellar reddening law; the phenomenon of circuinstellar dust complicated both of these efforts considerably. With the use of narrower bandpasses, the emission from circumstellar grains became an interesting subject of study in itself, as the grains around oxygen-rich and carbon-rich stars were found to have different spectral signatures. Data from the IRAS Low-Resolution Spectrometer have allowed several thousand circumstellar shells to be classified according to thickness and grain chemistry.
