Issei Yamamura

ASTRO-F is the second Japanese infrared space mission to be launched in early 2004. One of its focal-plane instruments, the Far-Infrared Surveyor (FIS), will carry out the whole sky survey in four-wavelength bands ranging from 50 to 200 μm. To evaluate the instrument performance and to prepare the data reduction system prior to the launch, we have developed a program to simulate the ASTRO-F/FIS sky survey, considering the basic instrumental proerties such as the diffraction pattern of the telescope, the detector pixel shape, and the readout electronics. In this paper, we focus on the validation of the hardware design of two long-wavelength (LW) bands covering 110-200 μm and 150-200μm. The stressed Ge:Ga detector arrays of 3x5 and 2x15 pixels are used for these two LW bands, respectively, In order to improve he spatial sampling frequency in the cross-scan direction, we tilted the FIS detector arrays by 26.5 degrees with respect to the scan direction. We demonstrate that this configuration actually provides better spatial information in the cross-scan direction. We evaluate the effective resolution of the FIS for the object with the different spectral energy distributions (SEDs). Since the full width at half maximum (FWHM) and the peak power of the images of point sources change significantly depending on the wavelength, color correction should be considered especially for the wide band in the data reduction processes. We scan a point ource locating at different relative positions from the scanning path, and examine how well we can determine the position and the power of the source. We assume an ideal situation; no noise, constant background, and monochromatic light. We find that fitting by the point spread function (PSF) is indispensable for the accurate measurement of the source flux and position. Since PSF changes with the color of the object, the shape of the PSF itself would be a fitting parameter. We find that second scan improves the reliability of the PSF fit.

Structure of the extended atmosphere in AGB stars has been investigated by analyzingH2O bands in the near-infrared region. Based on simple model analysis, we concluded that the time variation in the H2O bands with the variability phase can be attributed to the variation in the physical structure of the extended atmosphere, possibly caused by the shocks in the inner region. High wavelength/spatial resolution observations are crucial for further investigation of thestructure.