The Far-Infrared Surveyor (FIS) for AKARI

TLDR

The Far‑Infrared Surveyor (FIS) is one of two focal‑plane instruments on the AKARI satellite. The paper reports the in‑flight technical and operational performance of the FIS. FIS employs four photometric bands (65, 90, 140, 160 µm) with two array detector types and optics that scan the sky at high spatial resolution, and it also offers a Fourier‑transform spectrometer that uses the same detectors to produce simultaneous spectral maps. In orbit, FIS achieves a scan width over eight arcminutes, a pixel pitch at the diffraction limit, and PSFs matching the optical model except for a 30 % excess in the tails, while all functions perform well except the two longest‑wavelength bands, which fall short of laboratory expectations.

Abstract

Abstract The Far-Infrared Surveyor (FIS) is one of two focal-plane instruments on the AKARI satellite. FIS has four photometric bands at 65, 90, 140, and 160 $\mu \rm m$, and uses two kinds of array detectors. The FIS arrays and optics are designed to sweep the sky with high spatial resolution and redundancy. The actual scan width is more than eight arcminutes, and the pixel pitch matches the diffraction limit of the telescope. Derived point-spread functions (PSFs) from observations of asteroids are similar to those given by the optical model. Significant excesses, however, are clearly seen around tails of the PSFs, whose contributions are about 30% of the total power. All FIS functions are operating well in orbit, and the performance meets the laboratory characterizations, except for the two longer wavelength bands, which are not performing as well as characterized. Furthermore, the FIS has a spectroscopic capability using a Fourier transform spectrometer (FTS). Because the FTS takes advantage of the optics and detectors of the photometer, it can simultaneously make a spectral map. This paper summarizes the in-flight technical and operational performance of the FIS.