The infrared excess of alpha Lyrae.

A simple model is presented to explain IRAS and KAO far-infrared data of Alpha Lyrae in the 12-193 micron region in terms of dust grains of 10-micron size and temperatures of 130 + or - 15 and 40 + or - 5 K. It is suggested that silicates are constituents of the dust envelope, and that the far-IR flux varies as lambda exp(-beta), with beta = 3.0-3.8, in contrast with the usual indices considered. The results support the interpretation of Alpha Lyrae's far-IR excess as emission from a circumstellar shell of large size grains, though the model will not support grains larger than 10 microns size.