FIS: Far-Infrared Surveyor onboard ASTRO-F (IRIS)

The Far-Infrared Surveyor (FIS) is one of the focal plane instruments of ASTRO-F (IRIS: Infrared Imaging Surveyor) which is a Japanese infrared astronomical satellite and is planned to launch in 2003. The FIS is designed primarily to perform an all-sky survey with 4 photometric bands in wavelength range of 50-200 mu m by using unstressed and stressed Ge:Ga 2-D array detectors. The sensitivity of the FIS is 10-100 times higher than the IRAS (Infrared Astronomical Satellite) because of the improvement in detector performance based on recent advances in the device technology. The FIS also has spectroscopic capability by a Fourier spectrometer covering 50-200 cm(-1) in wavenumber with spectral resolution of 0.2 cm(-1). The same detector arrays for the all-sky survey are used, and these two functions are switched. The spectroscopic function is operated in the pointing mode. Spectral information can be used to estimate the redshifts of strange objects detected by the all-sky survey. Furthermore, many spectral lines in far-infrared wavelength can be detected from star forming region with its spectral resolving power. Hence the spectrometer is a powerful instrument to reveal the physical properties of galactic and proto-stellar sources. The ASTRO-F project is currently in its final stage of proto-model, which is constructed same as flight-model. Since instrumental goals of the FIS are unprecedented achivement of high sensitivity and high spatial resolution in far-infrared wavelength, the proto-model stage is important to prove the performance as the flight instrument. We mainly present here the latest optical, thermal, and mechanical properties of the proto-model of the FIS.