Narrow-band infrared photometry of α Ori

Abstract

Broad-band infrared photometry of cool giants and supergiants shows that many of these stars have appreciable excess emission at 10 and 22 μm (N and Q magnitudes brighter than expected from the temperatures deduced from shorter wavelengths). Gillett, Low and Stein showed that the 10 μm excess in several stars, including α Ori (M5Ia), was confined to a band peaking at about 10 μm. Woolf and Ney suggested that this emission peak corresponds to a peak in the emittance of silicate materials and that circumstellar dust composed of silicate produces the excess emission by thermal reradiation of starlight. In order to provide an additional experimental test of this hypothesis we have made a series of narrow-band photometric observations of the star α Ori, extending out to 24.5 μm. The spectral emittance of silicates is known to have a second peak near 20 μm which should be even more diagnostic than the 10 μm peak.