中川 貴雄

The far-infrared surveyor (FIS) is one of the focal-plane instruments on the ASTRO-F mission which will be launched in early 2004. The purpose of the FIS is to perform an all-sky survey in the wavelength range 50-200 μm. We are developing a suite of software that simulates the observations with this instrument to check the performance of the ASTRO-F/FIS as a whole and to prepare input data sets for the data analysis and reduction software prior to launch. The detection limit of the FIS is affected by many factors: the performance of the entire system, the brightness of sky and telescope emission, readout process, and the distribution of the celestial sources. The input model for FIS simulator consists of a catalogue of extragalactic point sources generated from the luminosity function at 60 μm, and a redshift distribution incorporating pure luminosity evolution (Ω =1, Λ=0). We present the expected source count results from the FIS survey and estimate the limiting redshift as ∼2.5 in the band at 50-110 μm and ∼3 in the band at 110-200 μm. © 2004 COSPAR. Published by Elsevier Ltd. All rights reserved. 0

We present the current status of the SPICA (space infrared telescope for cosmology and astrophysics, previously known as the HII/L2 mission). Onboard SPICA, a 3.5 m telescope cooled to 4.5 K provides an unprecedented combination of sensitivity and resolution for mid- to far-infrared observations (core wavelength between 5 and 200 μm). SPICA will make great contributions in many areas of astrophysics. We propose a "warm launch", cooled telescope concept for SPICA: the telescope is to be launched at ambient temperature and is to be cooled to 4.5 K in orbit by a modest mechanical cooler system with the assistance of effective radiative cooling. We have been working on development programs focusing on two key technical issues: reliable mechanical coolers and the light-weight telescope system. The target launch year of SPICA is around 2010. © 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

The features of HERSCHEL telescope being manufactured by EADS-ASTRIUM which will extend its technology to the SPICA Telescope, are discussed. HERSCHEL operates in the spectral range between 80 and 670 μ wavelength and is devoted to astronomical investigations in the far-infrared, sub-millimeter and millimeter wavelength range. the concept for the HERSCHEL telescope is based on an axisymetric, 3.5-m-diameter Cassegrain design. The main feature developed is the preliminary design of the SPICA telescope and the predicted performances which are taking advantage from the Silicone Carbide properties developed for HERSHEL telescope.

Ultimately, after the Single Aperture Far-IR (SAFIR) telescope, astrophysicists will need a far-IR observatory that provides angular resolution comparable to that of the Hubble Space Telescope. At such resolution galaxies at high redshift, protostars, and nascent planetary systems will be resolved, and theoretical models for galaxy, star, and planet formation and evolution can be subjected to important observational tests. This paper updates information provided in a 2000 SPIE paper on the scientific motivation and design concepts for interferometric missions SPIRIT (the Space Infrared Interferometric Telescope) and SPECS (the Submillimeter Probe of the Evolution of Cosmic Structure). SPECS is a kilometer baseline far-IR/submillimeter imaging and spectral interferometer that depends on formation flying, and SPIRIT is a highly-capable pathfinder interferometer on a boom with a maximum baseline in the 30 - 50 m range. We describe recent community planning activities, remind readers of the scientific rationale for space-based far-infrared imaging interferometry, present updated design concepts for the SPIRIT and SPECS missions, and describe the main issues currently under study. The engineering and technology requirements for SPIRIT and SPECS, additional design details, recent technology developments, and technology roadmaps are given in a companion paper in the Proceedings of the conference on New Frontiers in Stellar Interferometry.

We present pre-flight performance of a monolithic Ge:Ga array detector for Far-Infrared Surveyor (FIS) onboard the ASTRO-F satellite. The primary purpose of the ASTRO-F mission is to perform an all-sky survey in four photometric bands form 50-200 μm. For shorter half of this spectral range, 50-110 μm, we have developed the monolithic Ge:Ga array which is directly connected to a cryogenic readout electronics (CRE) with the indium-bump technology. In order to investigate the point-source detectability in the survey observation, we carry out a simulation experiment. The experiment was done by taking a image of moving pinholes located on the focal plane of the FIS optics. A clear image without any distortion was obtained, but the size of point source image is slightly larger than expected. We estimate the detection limit in the survey observation by taking account of all detector properties including the imaging performance. The results show that the detector sensitivity is sufficiently high to meet the requirement of the ASTRO-F mission.

Placed on the L2 Lagrangian point, the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) will operate in the 5 to 200 μm wavelength range, at 4.5K. The large aperture telescope (3.5m diameter in a single piece) requires a strong manufacturing mastering, associated with high technical performances. The background acquired by EADS-Astrium (France) on the 3.5m Silicone Carbide Herschel Telescope is a key for the success of the SPICA development. EADS-Astrium has been awarded by the Japan Aerospace Exploration Agency (JAXA) and Sumitomo Heavy Industries to assess the feasibility of the 3.5m all SiC telescope through a design phase contract. The Telescope driving requirements are the large diameter of 3.5m especially critical for the manufacturing aspects, and the Wave Front Error which has to be kept below 350nm rms over a large temperature range from ambient to the operational temperature of 4.5K which requires a strong mastering of the distortions.

The SPICA (Space Infrared Telescope for Cosmology and Astrophysics), which is a Japanese astronomical infrared satellite project with a 3.5-m telescope, is scheduled for launch in early 2010s. The telescope is cooled down to 4.5 K in space by a combination of mechanical coolers with an efficient radiative cooling system. The SPICA telescope has requirements for its total weight to be lighter than 700 kg and for the imaging performance to be diffraction-limited at 5 μm at 4.5 K. Two candidate materials, silicon carbide (SiC) and carbon-fiber-reinforced SiC (C/SiC composite), are currently under investigation for the primary mirror. A monolithic mirror design will be adopted in both cases because of the technical feasibility and reliability. This paper reports the current design and status of the SPICA telescope together with some of our recent results on laboratory cryogenic tests for the SiC and C/SiC composite mirrors.

This paper describes that the feasibility of the next Japanese infrared astronomical SPICA mission is verified in thermal design by numerical analyses and developed technologies. In this advanced cryogenic mission, in order to cool the large primary mirror and focal plane instruments down to 4.5 K for 5 years or longer without cryogen, the mechanical cooling is employed with effective radiant cooling, which compensates the limited cooling capacity of the JT cryocooler for 4.5 K upgraded from that developed for the "JEM/SMILES" mission on the International Space Station. First, thermal design of the telescope is numerically discussed with thermal mathematical models. Some configurations of radiators, shields and solar-array paddles are investigated and compared in technical and mission feasibilities. Next, the development status of the He-JT circuit with the Stirling cryocooler for one detector operated at the lowest temperature of 1.7 K is reported. The recent results of experiments give that the breadboard model of the 1.7 K cryocooler successfully exceeds the required cooling capacity of 10mW at 1.7K with small power consumption. Finally, the heat rejection system from those cryocoolers is discussed. As a promising candidate, the loop heat pipe is chosen and suitably designed. 3

We report the surface structure and roughness of the mirrors made of carbon fiber reinforced silicon carbide (C/SiC) composite improved for the SPICA (Space Infrared telescope for Cosmology and Astrophysics) mission. The improved C/SiC is a candidate of material for the SPICA light weight mirrors because of its superior properties: high toughness, high stiffness, small thermal deformation, feasibility to make large single dish mirror, low cost, and short term for production. The surface of the bare C/SiC composite consists of carbon fiber, silicon carbide and silicon, each of which has different hardness, so it is difficult to polish this surface smoothly. Our improved polishing technique achieved the surface roughness of better than 20nm RMS for the C/SiC composite flat mirror, which satisfies the requirement of the SPICA mission. For curved bare surface of the C/SiC mirror, the roughness is larger than 30 nm and now under improving. The Change of Bidirectional reflectance distribution function (BRDF) of the bare C/SiC composite at cryogenic temperature was measured with 632.8nm lasar. No significant difference was found between the BRDFs at 95K and that at room temperature. In order to improve surface roughness further, we are planning to apply the SiSiC slurry coating on the surface of the improved C/SiC composite. This combination can realize the surface roughness well enough to be applied even for optical telescopes.

We have developed the imaging Fourier Transform Spectrometer (FTS) for the FIS (Far-Infrared Surveyor) onboard the ASTRO-F satellite. A Martin-Puplett interferometer is adopted to achieve high optical efficiency in a wide wavelength range. The total optical efficiency of this spectrometer is achieved 40-80% of the ideal value which is 25% of the incident flux. The wavelength range of 50-200μm is covered with two kinds of detector; the monolithic Ge: Ga photoconductor array for short wavelength (50-110μm) and the stressed Ge:Ga photoconductor array for long wavelength (110-200μm). The spectral resolution expected from the maximum optical path difference is 0.18cm . In order to evaluate the spectral resolution of the FTS, we measured absorption lines of H O in atmosphere using the optics of the FTS with a bolometer at the room temperature. The measured line widths are consistent with the expected instrumental resolution of 0.18 cm . Some spectral measurements at the cryogenic temperature were carried out by using cold blackbody sources whose temperatures are controlled in a range from 20 to 50 K. The derived spectra considering with the spectral response of the system are consistent with expected ones. Spectroscopic observations with the FTS will provide a lot of astronomical information; SED of galaxies detected in the all sky survey and the physical diagnostics of the interstellar matter by using the excited atomic or molecular lines. -1 -1 2

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 50μm to 200μm. 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 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. -1

One of the key technologies for next generation space telescope with a large-scale reflector is a material having high specific strength, high specific stiffness, low coefficient of thermal expansion and high coefficient of thermal conductivity. Several candidates such as fused silica, beryllium, silicon carbide and carbon fiber reinforced composites have been evaluated. Pitch-based carbon fiber reinforced SiC composites were developed for the SPICA space telescope mirror to comply with such requirements. Mechanical performance such as bending stiffness, bending strength and fracture toughness was significantly improved. Evaluation procedures of thermal expansion and thermal conductivity behavior at cryogenic temperatures (as low as 4.5K) were established and excellent performance for the SPICA mirror was demonstrated.

We present the first results of an observational programme undertaken to map the fine structure line emission of singly ionized carbon ([CII] 157.7409 μm) over extended regions using a Fabry Perot spectrometer newly installed at the focal plane of a 100 cm balloon-borne far-infrared telescope. This new combination of instruments has a velocity resolution of ∼200 km s and an angular resolution of 1′.5. During the first flight, an area of 30′ × 15′ in Orion A was mapped. These observations extend over a larger area than previous observations, the map is fully sampled and the spectral scanning method used enables reliable estimation of the continuum emission at frequencies adjacent to the [CII] line. The total [CII] line luminosity, calculated by considering up to 20% of the maximum line intensity is 0.04% of the luminosity of the far-infrared continuum. We have compared the [CII] intensity distribution with the velocity-integrated intensity distributions of CO(1-0), CI(1-0) and CO(3-2) from the literature. Comparison of the [CII], [CI] and the radio continuum intensity distributions indicates that the largescale [CII] emission originates mainly from the neutral gas, except at the position of M 43, where no [CI] emission corresponding to the [CII] emission is seen. Substantial part of the [CII] emission from here originates from the ionized gas. The observed line intensities and ratios have been analyzed using the PDR models by Kaufman et al. (1999) to derive the incident UV flux and volume density at a few selected positions. The models reproduce the observations reasonably well at most positions excepting the [CII] peak (which coincides with the position of θ Ori C). Possible reason for the failure could be the simplifying assumption of a homogeneous plane parallel slab in place of a more complicated geometry. -1 13 1

Two types of gallium-doped germanium (Ge:Ga) detector arrays, stressed and unstressed, are to be on-board ASTRO-F, the next Japanese infrared astronomical satellite. Prior to prelaunch calibration of such detector arrays, we investigated transient properties of a one-element stressed Ge:Ga detector. In order to obtain calibration data for ASTRO-F, we measured the response under wide ranges of signal and background photon influxes. For the purpose of estimating effects of cosmic-ray impacts, we have also performed γ-ray irradiation of the detector by radioactive sources Co and Cs, and investigated differences in detector performance before and after the irradiation. 60 137

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 a whole sky survey in four wavelength bands covering between 50 and 200 μm. To evaluate the instrument specifications and to prepare input data for the reduction system, to construct them and to check their quality prior to the launch, we have developed a program to simulate the ASTRO-F/FIS sky survey, considering the basic instrumental properties such as diffraction pattern of the telescope, detector pixel shapes, and the data acquisition system. We evaluate the effective resolution of the FIS for objects with different spectra. Since full width at half maximum and the peak power of the images of point sources changes depending on the wavelength, colour correction should be taken into account, especially for the wide bands, in the data reduction processes.

To our knowledge, we are the first to successfully report a direct hybrid two-dimensional (2D) detector array in the far-infrared region. Gallium-doped germanium (Ge:Ga) has been used extensively to produce sensitive far-infrared detectors with a cutoff wavelength of 110 μm (2.7 THz). It is widely used in the fields of astronomy and molecular and solid spectroscopy. However, Ge:Ga photoconductors must be cooled below 4.2 K to reduce thermal noise, and this operating condition makes it difficult to develop a large format array because of the need for a warm amplifier. Development of Ge:Ga photoconductor arrays to take 2D terahertz images is now an important target in such research fields as space astronomy. We present the design of a 20 × 3 Ge:Ga far-infrared photoconductor array directly hybridized to a Si p-type metal-oxide-semiconductor readout integrated circuit using indium-bump technology. The main obstacles in creating this 2D array were (1) fabricating a monolithic Ge:Ga 2D array with a longitudinal configuration, (2) developing a cryogenic capacitive transimpedance amplifier, and (3) developing a technology for connecting the detector to the electronics. With this technology, a prototype Ge:Ga photoconductor with a direct hybrid structure has shown a responsivity as high as 14.6 A/W and a minimum detectable power of 5.6 × 10 W for an integration time of 0.14 s when it was cooled to 2.1 K. Its noise is limited by the readout circuit with 20 μV/Hz at 1 Hz. Vibration and cooling tests demonstrated that this direct hybrid structure is strong enough for spaceborne instruments. This detector array will be installed on the Japanese infrared satellite ASTRO-F. © 2003 Optical Society of America. -17 1/2

The IRTS data archive has been in public since 2002. IRTS surveyed about 7 per cent of the whole sky with four instruments, which covered from 1.4 to 700 μm. Presently the archive includes the near- and mid-infrared low resolution spectral catalogues of point sources, and image maps in five wavelength bands in the far-infrared. The point source catalogues contains over 14 000 (near-infrared) and 500 (mid-infrared) sources. The majority of detected sources are late-type stars. These large samples of uniform spectra are especially useful for statistical studies of infrared properties of stars. The far infrared image maps are obtained for the 158 μm [C II] line, and continuum bands at 155, 250, 400, and 700 μm. Radiation from the diffuse interstellar components has been studied with these data. More data products will be available in a few year time-scale. The IRTS data can be accessed via ISAS's data archive service DARTS, URL: http://www.darts.isas.ac.jp/.

This paper describes the thermal design of the space infrared telescope "SPICA". This advanced astronomical mission has innovative features in sensitivity and resolution. The performance of telescope is realized by the primary mirror of 3.5 m diameter and optical instruments cooled to 4.5 K or below. Thus, the cryogenic telescope requires efficient cooling system consisting of efficient radiators and mechanical cryocoolers. First, the configuration of radiators, shields and solararray- paddles are analyzed to estimate the mission feasibility in view of thermal design. Secondly, the developed mechanical cryocoolers are described. The BBM of He-JT cryocooler for 1.7 K successfully reaches the required cooling capacity of 10mW@1.7K in ground experiments. Finally, the loop heat pipe is numerically designed as the heat rejection system. Specifications and configurations of the LHP are shown. © 2003 by H. Sugita. Published by the American Institute of Aeronautics and Astronautics, Inc. 3

The recent activity in balloon-borne infrared observations in Japan is reviewed. Following this, the new balloon-borne telescope project is described. Near- and far-infrared diffuse emissions from the galaxy were firstly surveyed by the balloon telescopes of Japanese groups. In addition to this, the wide area survey of [CII] 158 micron line emission was extensively executed. Those results revealed the large-scale structures of stars and the interstellar medium of the Galaxy. The new project, FIRBE (Far-Infrared Balloon-Borne Experiment), is a successor of them. The FIRBE project is focused on mapping of the far-infrared emission from the Galaxy and external galaxies with the same spatial resolution as that of the IRAS. This is an on-going project, and we are making balloon flights in Japan and in India. © 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

We describe the development of a stressed Ge:Ga array detector with a large pixel format but a compact mechanical structure. The detector will be deployed in IRIS, a Japanese satellite to be launched in 2004, which will conduct an all-sky, far-infrared survey as well as spectroscopic observations of specific objects. The array has a 5 × 15 pixel format. Three of the five rows are for the 100 - 200 μm band, and the other two are for the 150 - 200 μm band. In the focal plane of the IRIS telescope, each pixel corresponds to a field of view of 50″ × 50″. A uniaxial mechanical stress is applied to the detector chips in each row using a single stressing mechanism. This results in a compact focal-plane array. Light pipes with entrance apertures of 0.9 × 0.9 mm size are distributed with a pitch of 1 mm. A charge-integrating amplifier (CIA) circuit is used as the readout. Bare-chip amplifiers and multiplexers are placed behind the Ge:Ga chips and are cooled to 1.8 K. The entire system, including chips and readouts, weighs 300 grams. We have thus-succeeded in building a compact array detector suitable for a satellite payload. © 2002 Published by Elsevier Science Ltd on behalf of COSPAR.

The spectral characteristics of the diffuse galactic mid- and far infrared emission at λ = 10 - 60 μm are investigated using the IRTS and IRAS data. We estimate the grain temperature, total far-infrared intensity (FIR) and radiation density from the emission of the large grains at λ > 100 μm, assuming that the spectrum has a single temperature Planck function with a λ emissivity law. We found that the spectral energy distribution of the diffuse galactic emission at wavelengths from 10 μm to 1 mm changed as a function of the dust temperature. In addition, we found clear correlation for the intensity of emissions at 12, 25, and 60 μm. The 12 μm intensity is proportional to FIR, and the ratios of the 25 and 60 μm intensities to FIR are proportional to the strength of the interstellar radiation field. These correlations are consistent with those found in the data of seven H II regions with various physical conditions. This suggests that the emitters of the emission at 12-60 μm are well mixed with large grains radiating at wavelength greater than 100 μm and implies that the ratio of the mass of these emitters to the mass of the large grains is constant in interstellar space. We conclude that the 12 μm emission is largely due to unidentified infrared features and that the 25 and 60 μm emission arises from very small grains transiently heated by multiple-photon © 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved. -2

We have successfully developed a low-power, low-noise silicon p-channel MOSFET working at 1.8 K. This MOSFET was produced by a standard 0.5μm BiCMOS process. From the typical current-voltage characteristics of this p-channel MOSFET at 1.8K, we obtained that the drain resistance r is ∼2MΩ, the transconductance g is ∼35μS, and the input referred noise voltage is as low as ∼2μV / √Hz at 1Hz under low-drain current condition (∼1μA). No "kink" like behavior was observed within the nominal operation range (-1.5V < V <0V). These results are acceptable for the application to cryogenic electronics. The purpose of the present work is to develop the capacitive transimpedance amplifiers (CTIA) for the Far-infrared Surveyor (FIS) on board the Japanese infrared astronomical satellite, ASTRO-F. The cryogenic amplifier that is essential for CTIAs was successfully made by employing this p-channel MOSFET. The open-loop gain was ∼1000, and the power consumption was less than 10μW at 4.2K. We have finally demonstrated that the CTIA consisting of this cryogenic amplifier worked well at 4.2K. © 2002 Published by Elsevier Science Ltd on behalf of COSPAR. d m ds

The Far-Infrared Line Mapper (FILM) onboard the Infrared Telescope in Space (IRTS) made a survey for the far-infrared [C II] 158 μm line emission with high sensitivity and moderate spatial resolution. We have found that diffuse [C II] line emission extends to high Galactic latitude regions. The [C II] line intensity at |b| ∼ 60° ranges from 2 × 10 to 1.5 × 10 erg cm s sr . Comparisons of the distribution of the [C II] line emission with those of the H I column density and far-infrared radiation show some correlations, but the [C II] line emission differs from the far-IR and HI emission at high Galactic latitudes. These differences suggest that the [C II] line primarily comes from ionized gas in the high-latitude regions. The intensities of the [C II] line emission on the southern side (b < 0°) of the Galactic plane are systematically larger than those on the northern side (b > 0°). We infer from this difference that there is a displacement of the Sun with respect to the center of interstellar medium from which the [C II] line comes. When an exponential distribution is assumed for the [C II] emitting gas, it is expected that the Sun is located at the distance of about 17% of the scale height above the center of the gas. This is consistent with the previously reported displacement of the Sun from the Galactic plane. -7 -6 -2 -1 -1

Two types of gallium-doped germanium detector arrays, stressed and unstressed ones, are onboard ASTRO-F, the next Japanese infrared astronomical satellite. Prior to measurements of such detector arrays, we investigated the transient properties of a single-element stressed gallium-doped germanium detector. In order to obtain calibration data for ASTRO-F, our measurements cover wide ranges of signal and background photon flux levels. The current status of our experiment is described in this paper. © 2002 Published by Elsevier Science Ltd on behalf of COSPAR.

We review Japanese activities of balloon-borne far-infrared astronomical spectroscopic observations. Most of our experiments have focused on spectroscopic mapping observations of the far-infrared [C II] line at 158 μm, which is the dominant coolant of general interstellar gas and is a key tracer of interstellar energetics. We made two types of observations. One is large-scale survey observations with a dedicated system which has an offset low-emissivity telescope. The other is detailed observations of individual sources with a multi-purpose 50 cm telescope. In addition to the conventional spatial chopping method, we used spectral modulation techniques with a Fabry-Perot spectrometer in these experiments to make efficient mappings of spatially extended sources. Major scientific results of these experiments are briefly reviewed. New collaborative project with TIFR, India started in 1998, to make high-resolution spectroscopic mapping observations of star-forming regions with the TIFR 1 m telescope and the Japanese Fabry-Perot spectrometer. © 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

We present the concept of the SPICA (Space Infrared Telescope for Cosmology and Astrophysics, previously known as HII/L2) mission, which incorporates a 3.5 m telescope cooled to 4.5 K. SPICA will focus on high-resolution mid- to far-infrared observations with unprecedented sensitivity. It will make great contributions to our understanding of basic astronomical questions, such as the history of star-formation in the universe, the birth and evolution of Active Galactic Nuclei (AGN), the formation of planets in extrasolar systems, and the history of our solar system. We propose a "warm launch" cooled telescope concept for SPICA; the telescope is to be launched at ambient temperature and is to be cooled in orbit to 4.5 K by a modest mechanical cooler system with the assistance of effective radiative cooling. SPICA is proposed to be launched into a halo orbit around one (L2) of the Sun-Earth libration points in 2010. © 2002 Published by Elsevier Science Ltd on behalf of COSPAR.

ASTRO-F is a Japanese infrared satellite, which is scheduled for launch in early 2004. Far-infrared instrument that will be onboard ASTRO-F, Far-Infrared Surveyor (FIS), will perform the four-color all sky survey in the 50-200 μm wavelength range with the diffraction-limited spatial resolution for 67-cm diameter telescope. For short-wave photometric bands of 50-110 μm, we have developed a monolithic Ge:Ga two-dimensional array detector with no light cavity. This top-illumination type array design is promising for making future large-format array. The monolithic Ge:Ga is directly attached onto cryogenic readout electronics, capacitive trans-impedance amplifier composed of silicon p-MOSFETs, designed specially for low-temperature use. Results of the detector measurements show that the device works properly and sensitive enough for astronomical applications. Complex behavior of the detector, such as non-linearity of the integration ramp, transient response, non-uniform responsivity in the array, and cross-talk response, which may cause systematic error in the photometry, have been found. But, these effects are ∼10% of major part of the signal and correctable with accuracy of a few %.

The Japanese infrared astronomical satellite, ASTRO-F, employs the Far-Infrared Surveyor (FIS) for all sky survey. The FIS has two detector arrays; one covers from 50 to 110 μm wavelength, the other covers from 110 to 200 μm. Each of them uses Ge:Ga operating at 2K. We have developed and evaluated the preamplifiers for these detector arrays. The preamplifiers are required to work at 2K with low noise and low power dissipation. In this paper, we report on the development and evaluation of these cryogenic preamplifiers.

Far-Infrared Surveyor (FIS) is one of the two focal plane instruments of ASTRO-F which is a Japanese infrared astronomical satellite and is planned to launch in 2004. The FIS has spectroscopic capability by a Fourier transform spectrometer (FTS) covering 50-200 cm with spectral resolution of 0.2-0.33 cm in addition to the primary purpose of FIS (an all-sky photometric survey). The Martin-Puplett interferometer is adopted as the method for spectroscopy in order to achieve high optical efficiency in a wide wavelength range. The most important issue of the FTS is the development of driving mechanism in order to scan a moving mirror with high optical performances. By the present we succeed to develop the driving mechanism satisfying a lot of limitations and requirements as a instrument onboard satellite. Furthermore the wire-grid polarizers are evaluated in optical performance, these are usable for polarized interferomter. We also measure FIR spectrum using Spectroscopy mode of FIS, and many absorption lines of H O are detected on continuum spectrum of atmosphere. And the interferogram and spectrum are derived at low temperature (2K) that is practically used in space. The spectrum resembles expected one which are considered with optical components for flight model. The detection limit are estimated combining performances of optical components and detectors, the FISP has sufficient performance to archive objective sciences. FTS will provide a lot of astronomical information; determination of the SED in high-z objects detected by the survey observation of ASTRO-F, the redshift of such objects, and the physical conditions that are hard to be derived by optical/NIR-MIR observations, from FIR lines. -1 -1 2

The telescope onboard Japanese infrared astronomical satellite, ASTRO-F, forms an F/6 Ritchey-Chretien system with a primary mirror of 670 mm in diameter, the total weight of which is about 42 kg. The primary and secondary mirrors are made of a sandwich-type SiC material, consisting of right porous core and dense CVD coat of SiC. The whole system will be cooled down to 5.8 K with a combined use of super-fluid liquid helium and mechanical coolers on orbit. In order to estimate optical performance of the flight-model telescope at operating cryogenic temperatures, the primary mirror alone was first cooled and tested, and then the whole telescope assembly was tested at cryogenic temperatures. In both cases, the changes in the surface figure were measured from outside the cryostat by an interferometer for the temperature range of 10 K to 300 K. As a result, non-negligible degradation in wave-front errors of the primary mirror and the telescope assembly was detected at low temperatures. The deformation of the primary mirror was found to be mainly due to the thermal contraction of support structures and heat anchors, and degradation by the SiC mirror itself was much smaller. The observed wave-front error of the telescope assembly at 13 K, which was found to originate mainly from the distortion of the primary mirror, marginally meets the requirement to achieve the diffraction-limited performance at 5 microns. This paper summarizes the optical performances thus achieved at cryogenic temperatures for the ASTRO-F telescope.

We analyzed ASCA data of 28 luminous infrared galaxies including 16 ultraluminous infrared galaxies (ULIRGs) to study the nature of the AGN and to reveal the energy source of their far infrared luminosity. Our primary conclusion is that the circumnuclear starburst activity is the main energy source of most ULIRGs. We also found that the ULIRGs with unabsorbed AGN tend to have a narrow-line Seyfert I nucleus.

The spatial variation of the unidentified infrared (UIR) emission bands at 6.2, 7.7, 8.6, and 11.2 mum has been investigated in relation to the Far-Infrared (FIR) emission by the IRTS and the ISO observations in a wide sky area of various environments. The UIR/FIR ratio is found to be fairly constant over a wide range of different environments except for ionized regions, where UIR/FIR shows a noticeable decrease. There may also be a slight increase in the UIR/FIR ratio in surrounding regions of the ionized gas or interface regions to molecular clouds, suggesting possible enhancement in the abundance of UIR band carriers. In spite of the variation in UIR/FIR, the relative band strengths of the UIR bands do not show any systematic variation with UIR/FIR, indicating that the UIR band carriers are quite stable species and do not alter their properties appreciably over a wide range of physical conditions.

Using the mid-infrared spectrometer on board the Infrared Telescope in Space and the low-resolution grating spectrometer (PHT-S) on board the Infrared Space Observatory, we obtained 820 mid-infrared (5-12 μm) spectra of the diffuse interstellar medium (DIM) in the Galactic center, W51, and Carina Nebula regions. These spectra indicate that the emission is dominated by the unidentified infrared (UIR) emission bands at 6.2, 7.7, 8.6, and 11.2 μm. The relative band intensities (6.2/7.7 μm, 8.6/7.7 μm, and 11.2/7.7 μm) were derived from these spectra, and no systematic variation in these ratios was found in our observed regions, in spite of the fact that the incident radiation intensity differs by a factor of 1500. Comparing our results with the polycyclic aromatic hydrocarbons (PAHs) model for the UIR band carriers, we find that PAHs in the DIM have no systematic variation in their size distribution, their degree of dehydrogenation is independent of the strength of UV radiation field, and they are mostly ionized. The finding that PAHs in the DIM with low UV radiation field strength are mostly ionized is incompatible with past theoretical studies, in which a large fraction of neutral PAHs is predicted in this kind of environment. A plausible resolution of this discrepancy is that the recombination coefficients for electron and large PAH positive ion are by at least an order of magnitude less than those adopted in past theoretical studies. Because of the very low population of neutral state molecules, photoelectric emission from interstellar PAHs is probably not the dominant source of heating of the diffuse interstellar gas. The present results imply constant physical and chemical properties of the carriers of the UIR emission bands in the DIM covering the central and disk regions of the Galaxy, which could help in the identification of the carriers.

The conceptual SPICA mission is ambitiously intended to make high-resolution infrared astronomical observations. The spacecraft is to be launched by the H-IIA rocket into a halo orbit around S-E L2. Long-term observation with a large mirror is realized by advanced cryogenic technologies. The primary mirror is to be cooled to 4.5 K by modern mechanical cryocoolers with the assistance of effective radiative cooling. In this paper, numerical 3-D analyses are carried out to study basic thermal characteristics of the infrared telescope system. As a result, technical requirements for the mission have become clear.

We present the concept of the SPICA (Space Infrared Telescope for Cosmology and Astrophysics) mission, which incorporates a 3.5 m telescope cooled to 4.5 K. SPICA will focus on high-resolution mid-to far-infrared observations with unprecedented sensitivity. It will make great contributions to our understanding of important astronomical questions, such as the history of star-formation in the universe, the birth and evolution of AGN, and the formation of planets in extrasolar systems. In order to reduce the total weight, we propose a "warm launch" cooled telescope concept; the telescope is to be launched at ambient temperature and is to be cooled in orbit to 4.5 K by a modest mechanical cooler system with the assistance of effective radiative cooling. SPICA is proposed to be launched into a halo orbit around S-E L2 in 2010.

We present a conceptual design of a future infrared astronomical satellite: the HII/L2 mission. Its telescope is to be launched at ambient temperature (warm launch) and is to be cooled to 4.5 K by effective radiative cooling and mechanical cryogenic coolers. The warm launch design reduces the total weight dramatically. A 3.5 m class telescope can be put into a halo orbit around S-E L2 by the Japanese H-IIA launching vehicle. This mission focuses on high-resolution mid-to far-infrared observations with unprecedented sensitivity. The target launch year is 2010. © 2000 COSPAR. Published by Elsevier Science Ltd.

We have developed a new 50-cm infrared balloon-borne telescope. The first flight of this telescope system is scheduled for September, 1998. We used an offset paraboloidal mirror and used its primary focus to reduce the amount of background emission from the telescope itself in order to perform photometric observation with high sensitivity. The structure of the telescope is made of carbon fiber reinforced plastics (CFRP) to reduce its weight and make the optics free from thermal contraction due to low temperatures during observational flights to retain good focusing of the optics. For the detector, we use our newly developed 4 × 8 stressed Ge:Ga array in order to perform 150-180 μm photometry. The detector is installed in a cryostat and cooled by liquid He down to 2 K. The large format of the detector raises the observational efficiency enabling us to survey a wide area of the sky (up to 10° × 10°) with a high spatial resolution of 1.5′ in one observational flight. In the first flight, we plan to survey the Orion region, W51, etc. and to map some external galaxies. © 2000 COSPAR. Published by Elsevier Science Ltd.

We present a conceptual design of the infrared astronomical mission HII/L2, which incorporates a large, cooled telescope. We propose to cool a 3.5 m class telescope down to 4.5 K only by moderate mechanical cryogenic coolers with the help of effective radiative cooling. The Japanese H-IIA launching vehicle can put this 3.5 m telescope mission into a halo orbit around S-E L2. The cooled, large telescope makes the HII/L2 mission optimum for high-resolution mid- to far-infrared observations with unprecedented sensitivity. The target launch year is 2010.

We present a Grief description of an on-going Japanese infrared astronomical telescope mission in space: Infrared Imaging Surveyor (IRIS), as well as that of a future mission, a 3m class cooled telescope to be put into a halo orbit around the Sun-Earth L2 point by the Japanese H-IIA rocket(the HII/L2 mission). The IRIS is a 70cm cooled telescope dedicated to an infrared sky survey at 2 - 200 mu m. The HII/L2 mission is an ideal observatory-type platform to make follow-up observations to the IRIS survey mission. The mission is optimized for mid-infrared and far-infrared deep imaging and spectroscopic observations, thus will be complementary with NGST and FIRST. The target launch year is 2010.

Using the Mid-Infrared Spectrometer on board the Infrared Telescope in Space and the low-resolution grating spectrometer on board the Infrared Space Observatory, we obtained 850 mid-infrared (5 - 12 mum) spectra of the diffuse interstellar medium (DIM) in the Galactic center, W51, and Carina nebula regions. These spectra indicate that the emission is dominated by the unidentified infrared (UIR) emission bands at 6.2, 7.7, 8.6, and 11.2 mum The relative band intensities (6.2/7.7, 8.6/7.7, and 11.2/7.7 mum) were derived from these spectra, and no systematic variation in these ratios was found in our observed regions in spite of the fact that the total far infrared intensities differ by a factor of 100 (or G(0) approximate to 5 - 4000, with G(0) being the integrated radiation intensity in units of the solar neighborhood value). Our results imply constant physical and chemical properties of the carriers of the UIR emission bands in the DIM. Comparing our results with the polycyclic aromatic hydrocarbons (PAHs) model, we found that the candidate PAHs are mostly or completely ionized in the DIM. The finding that diffuse interstellar PAHs are mostly ionized is incompatible with past theoretical studies, in which a large fraction of neutral PAHs is predicted in low UV radiation environments such as the DIM. One possible resolution of this discrepancy is that the recombination coefficients for electron-PAH ion interactions are at least an order of magnitude less than those adopted in the past theoretical studies. If the PAH model requires a mixture of PAHs with different carbon atom sizes and degree of thermodynamical stabilities to fit the observed UIR emission bands, it may have difficulty to keep the constancy of this complex mixture of PAHs in the DIM covering a wide range of UV radiation field strengths. Larger PAHs may solve this problem.

We have developed the new balloon-borne telescope, Far Infrared Balloon-Borne Experiment (FIRBE), to survey the far-infrared radiations of star-forming regions. The primary mirror is an offset parabolid with a diameter of 50cm (F/2) and telescope structure is made form Carbon Fiber Reinforced Plastics (CFRP) to lighten the whole telescope and hold the strain of image at the focal position minimum since its thermal contraction is very small. The telescope optics is off-axis system with no secondary mirror and no warm support structure in its optical path in order to reduce the infrared emission from the telescope structure itself. Moreover the focused light is led directly into cryostat, in which a newly developed stressed Ge:Ga 2D array detector is cooled down to 2 K with liquid helium. These configurations lead us to the improvement in the sensitivity for infrared observation. The main onboard electronics consists of three CPUs. They engage in handling observational data, decoding commands, formatting the transmission data, and controlling the attitude of the telescope. The attitude control system is an alt-azimuth mounting. With referring to angle sensors such as three-axes fiber optics gyroscopes, onboard electronics drives the torque mechanism to control the telescope. Since the control law is calculated by onboard CPU digitally, we can control the telescope flexibly by changing control gains and prepare various control modes such as pointing, scanning, tracking, and so on. On the first flight attempted in Japan in 1998, we could achieve a good pointing stability of less than 30 arc-second. By using this telescope, we will make survey observations of 160-micron continuum for Galactic star-forming regions and external galaxies with the angular resolution of 1.5′.

We have developed a 4 x 8 array of stressed Ge:Ga detectors. This array detector has a high density format of entrance pupils so that we can minimize the size of the camera optics. The cutoff wavelength of the detector is about 170 μm, and the detector's NEP is better than 10 W Hz . We are going apply this array detector to balloon-borne astronomical observations. Furthermore, we are developing this detector into a 5 x 15 array detector that will be placed onboard the IRIS satellite to be launched in 2003. 16 -1/2

Gallium-doped germanium (Ge:Ga) extrinsic semiconductor has been used as sensitive far-infrared detectors with a cutoff wavelength of 110 micron (2.7 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 (2D) THz images is now an important target for research fields such as the space astronomy. We present the basic idea of a 20×3 Ge:Ga far-infrared photoconductor array directly hybridized to a Si p-MOS readout integrated circuit (IC) using indium bump technology, which is an advanced structure for far-infrared detector arrays. The main issues to achieve in creating a 2D array are summarized as follows: the fabrication of a monolithic Ge:Ga 2D array with longitudinal configuration, development of the cryogenic readout electronics, and the development of technology for connecting the detector with the electronics. We report that the detector was cooled to 2.1 K, the best responsivity obtained was 16.2 A/W and the best NEP was 2.6 × 10 W/Hz at a bias field of 1.2 V/cm. We demonstrated that p-MOS FETs can be used as the cryogenic readout electronics. And we succeeded in the far-infrared detection by using direct hybrid structure photoconductors. The results of vibration and cooling tests were conducted to confirm the strength of the direct hybrid structure. Our Ge:Ga photoconductor direct hybrid 2D array will be an excellent device for taking 3 THz images. -17 1/2

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 μm 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 in wavenumber with spectral resolution of 0.2 cm . 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. -1 -1

Two HII regions, the Carina nebula and Sharpless 171, and the rho Oph cloud region, have been mapped with PHT-S and LWS full grating scan (45-170 mu m). The unidentified infrared (UIR) emission bands at 6.2, 7.7, 8.6, and 11.2 mu m were detected at most observed positions. Their spatial variations are examined in relation to the far-infrared emission from the submicron dust grains. The temperature and optical depth of submicron grains are derived from the fit of the LWS spectra with modified blackbody. The strength of the incident radiation field in units of the solar vicinity value (G(0)) is estimated from the dust temperature. The ratio of the UIR 7.7 mu m band to the total far-infrared intensity (FIR) shows a similar trend in the two HII regions. It decreases as G(0) increases for G(0) &gt; 1000. The ratio, however, stays constant in the rho Oph region, even for G(0) &gt; 1000. A more general relation is found if the ratio is plotted against [OIII] 88 mu m line intensity divided by FIR. The plot indicates that the UIR band carrier may be destroyed or the emission mechanism becomes inefficient in ionized regions. On the other hand, the relative band strengths among the UIR bands do not show any systematic trend with the radiation strength or ionization, indicating that the material properties of the UIR band carrier do not vary appreciably with the radiation field.

We are developing a 20 × 3 Ge:Ga far-infrared photoconductor array directly hybridized to a Si p-MOS readout integrated circuit (IC) using indium bump technology. We describe the design of the detector array, as well as its fabrication process and performance.

We observed the nearby low-metal galaxies IC 5152 (lacking active star formation) and I Zw 36 (a blue compact) in the [C II] 158 mu m fine-structure emission with ISO/LWS. The observed ratios are not so large as that in Magellanic type of galaxies. This indicates that large [C II]/CO (J = 1-0) flux ratios observed in the Magellanic types are also due to factors other than metallicity. We expect that more massive galaxies in early epoch have interstellar medium similar to that in blue compacts rather than in Magellanic types.

We are developing a stressed Ge:Ga 2D array detector that will be used for balloon-borne and satellite-born astronomical observations at wavelength between 100 and 200 micrometers. We have succeeded in making a 4 X 8 element stressed array detector with a stress of 600 N/mm and responsivity peak wavelength moved to about 165 micrometers. This has the largest number of pixels at the present time. The responsivities of the detector are high enough as well as those currently in use. This detector has a compact structure and a small total pixel size, and thus, it can be used for satellite-born instruments that have severe space limitation. ©2003 Copyright SPIE - The International Society for Optical Engineering. 2