Far-infrared surveyor: Design, operation, and performance

The Far-Infrared Surveyor (FIS) is a focal plane instrument of the ASTRO-F satellite, and is designed primarily to achieve far-infrared all sky survey with four photometric bands in wavelength range of 50mum to 200mum. Compared to IRAS, the FIS has higher sensitivity, higher spatial resolution, and longer wavelength coverage. The FIS also has spectroscopic capability with a Fourier transform spectrometer (FTS). In order to assemble these two kinds of instrument into a small and light body, we have developed new compact detector arrays and adopt the unique optical design. In the first half year of the ASTRO-F mission, the all sky survey is performed intensively, and is completed in the following half year. In addition to this survey, the telescope can be kept to a specific direction during 10 minutes for pointing observations. In pointing observations, we can take deep photometric images by using the photometric mode, or can take spectra by using the FTS. According to the laboratory calibration, it is expected that the detection limit of the all sky survey is almost one order of magnitude better than the IRAS one. The FTS could take spectra with full spectral resolution of 0.18cm(-1) for about two orders of magnitude brighter sources than the detection limit of the all sky survey for one pointing observation. Due to the imaging FTS, the observing efficiency is much improved for the extended sources. The FIS will provide us unique and valuable observational data in the far-infrared wavelength region.