Takao Nakagawa

Experimental studies are carried out to clarify the structures and erosive properties of rectangular cavitating jets. The jet is supplied from a high pressure pump and injected through a rectangular nozzle of aspect ratio of two or four. It discharges into a test cell at specified constant pressure and impinges against a test specimen of aluminum alloy. The structures of the jets are observed by instantaneous photographs and high-speed movies. The erosion tests are conducted at the injection pressure of 18 MPa and the cavitation number of 0.01, 0.02, and 0.03. It is shown that the structures of the cavitating jets issuing from the rectangular nozzles are completely different from those of circular cavitating jets. Corresponding to the jet structures, the erosive properties of the rectangular cavitating jets are different from those of the circular cavitating jets.

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.

The Far-Infrared Surveyor (FIS) is one of the on-board instruments on the ASTRO-Fsatellite, which will be launched in early 2004. The first a half year of its mission period of 500days is dedicated to an all sky survey in four bands between 50 and 200μm. On the basis of thepresent hardware specfications and configurations of the FIS, we have written a computer programto simulate the FIS. The program can be used to evaluate the performance of the instrument aswell as to produce input for the data reduction system. In this paper, we describe the currentstatus of the program. As an example of the usage of the simulation program, we present theexpected observing data for three different detector sampling rates. The functions which shouldbe implemented into the program, in the future, are enumerated.

Current idea of focal plane instruments onboard HII/L2 (SPICA) mission is described.To squeeze out maximum scientific output, the instruments cover 2-200 μm in both imaging modeand spectroscopic mode.

Gallium-doped germanium (Ge:Ga) extrinsic semiconductors have been used as sensitive far-infrared detectors with a cutoff wavelength of 110μm (3 THz), especially in the fields of astronomy, the spectroscopy of molecules and solids, and plasma diagnostics. Developing Ge:Ga photoconductor arrays to take two-dimensional THz images is now an important target for such research fields as the space astronomy. We are developing Ge:Ga far-infrared photoconductor direct hybrid arrays for use as focal-plane detectors in the Far Infrared Surveyor (FIS), one of the two main instruments of the Infrared Imaging Surveyor (IRIS) satelite that will be launched in 2003. In this paper, we report on the basic idea of a 20×3 Ge:Ga far-infrared photoconductor array directly hybridized to a Si p-MOS readbut integrated circuit (IC) using indium bump technology, and give the results of vibration and cooling tests conducted to confirm the strength of the direct hybrid structure.