Low-temperature optical properties of silicate particles in the far-infrared region

The far-infrared absorption spectra of crystalline circumstellar dust analo gues (orthoenstatite? clinoenstatite, diopside, and forsterite) were measur ed at room temperature (295 K) and liquid-helium temperature (4.2 K). The w avelength ranges of the measurements were 20-80 mum and 30-80 Irm at 295 K and 4.2 K, respectively. The absorption bands were detected very clearly no t only at room temperature, but also at liquid-helium temperature. The temp erature effects were clearly observed at liquid-helium temperature, such as (1) an increase in the spectral index of the continuum, (2) an enhancement in the absorption band strength, (3) a decrease in the band width, and (4) the absorption peaks of all bands of all samples shifted toward a shorter wavelength. These re suits suggest that a reconsideration of the identifica tion should be required for some absorption bands which have been recognize d as unidentified bands because of a disagreement in the peak position betw een the observed data and the laboratory data obtained at room temperature. Our experimental data can be obtained from the web-site (http://www.kyoto- phu.ac.jp/labo/butsuri/).