INFRARED PHOTOMETRY AND THE DETECTION OF CIRCUMSTELLAR DUST

The presence of dust grains in the circumstellar envelopes of many sta rs is known primarily from their effect on infrared energy distributio ns. The early development of wideband photometry in the infrared was m otivated by a desire to improve the effective temperature scale for co ol stars and to study the interstellar reddening law; the phenomenon o f circumstellar dust complicated both of these efforts considerably. W ith the use of narrower bandpasses, the emission from circumstellar gr ains became an interesting subject of study in itself, as the grains a round oxygen-rich and carbon-rich stars were found to have different s pectral signatures. Data from the IRAS Low-Resolution Spectrometer hav e allowed several thousand circumstellar shells to be classified accor ding to thickness and grain chemistry.