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We have developed a prototype half-wave plate (HWP) based polarization modulator (PMU) for Cosmic Microwave Background polarization measurement experiments. We built a 1/10 scaled PMU that consists of a 50 mm diameter five-layer achromatic HWP with a moth-eye broadband anti-reflection sub-wavelength structure mounted on a superconducting magnetic bearing. The entire system has cooled below 20 K in a cryostat chamber that has two millimeter-wave transparent windows. A coherent source and the diode detector are placed outside of the cryostat and the millimeter-wave goes through the PMU in the cryostat. We have measured the modulated signal by the PMU, analyzed the spectral signatures, and extracted the modulation efficiency over the frequency coverage of 34-161 GHz. We identified the peaks in the optical data, which are synchronous to the rotational frequency. We also identified the peaks that are originated from the resonance frequency of the levitating system. We also recovered the modulation efficiency as a function of the incident electromagnetic frequency and the data agrees to the predicted curves within uncertainties of the input parameters, i.e. the indices of refraction, thickness, and angle alignment. Finally, we discuss the implication of the results when this is applied to the LiteBIRD low-frequency telescope.

The Mid-Infrared Multi-field Imager for gaZing at the UnKnown Universe (MIMIZUKU) is developed as the first-generation mid-infrared instrument for the University of Tokyo Atacama Observatory (TAO) 6.5-m telescope. MIMIZUKU performs medium-band imaging and low-resolution spectroscopy in 2-38 microns and enables highest-spatial-resolution observations in the long-wavelength mid-infrared beyond 25 microns. In addition, MIMIZUKU has a unique opto-mechanical device called ‘Field Stacker’, which enables us to observe a distant (

Although astronomers have confirmed the existence of 4,000 exoplanets to date, it is still difficult to directly compare exoplanets with the planets in our solar system because most of the known transiting exoplanets have an orbital period shorter than 1 year. Recent analyses of the 4-year data from the Kepler spacecraft revealed dozens of long-period transiting exoplanets and showed that their abundance is of order unity around Sun-like stars. However, the stars targeted by Kepler are too faint to conduct follow-up observations. The on-going all-sky survey mission TESS, with four 10.5 cm cameras with a field of view of 24 deg x 24 deg, is finding nearby transiting planets; however, the nominal observation period (1 month{1 year) is too short to find long-period planets with au-scale orbits. Herein, we propose using the LOng-period Transiting exoplanet sUrvey Satellite (LOTUS) mission, which employs a 7.5 cm wide-field (33 deg x 33 deg) camera placed on a nanosatellite, to continuously monitor the same sky region and find long-period planets transiting nearby bright stars. We present a conceptual design for the optics and bus system of LOTUS. Our optical system has a uniform point spread function over the entire field of view and a wide wavelength range (0.5{1.0 um). The bus system is designed to ensure that the pointing precision is sufficient to achieve the sub-percent photometry required for the detection of transiting exoplanets.

We present the thermal characteristics of a superconducting magnetic bearing (SMB) system that is designed for a polarization modulator of a cosmic microwave background polarization experiment. The SMB system consists of a ring-shaped magnet and an array of YBCO tiles. Both have an opening diameter of about 400 mm. The ring-shaped magnet is formed by an array of segmented magnets. The magnetic field inhomogeneity of this rotor magnet is originated from the magnetic field inhomogeneity of each magnet and the spatial gap between the segments. This inhomogeneity can contribute as a source of friction, and thus a source of heat in an operation at below 10 K. We estimate the heat dissipation from friction of the SMB by conducting the spin-down measurements, and we projected the heat dissipation of 2–20 mW from the hysteresis contribution depending on the levitation height. We discuss the consistency of the spin-down measurements to Bean's model between the magnetic field inhomogeneity and the hysteresis loss. We also discuss the potential temperature rise of the rotor magnet when it is levitating at the temperature at around 10 K. Thus, we address the means to estimate the rotor temperature by the physical contact to the rotor. The extrapolated temperature recovers the rotor temperature with the difference of less than 2 K without any correction.

著者人数: 11名, Accepted: 2016-08-25, 資料番号: SA1160248000

Accepted: 2016-07-06, 資料番号: SA1160250000

We propose an all-silicon multi-layer interference filter composed solely of silicon with sub-wavelength structure (SWS) in order to realize high performance optical filters operating in the THz frequency region with robustness against cryogenic thermal cycling and mechanical damage. We demonstrate fabrication of a three-layer prototype using well-established common micro-electro-mechanical systems (MEMS) technologies as a first step toward developing practical filters. The measured transmittance of the three-layer filter agrees well with the theoretical transmittances calculated by a simple thin-film calculation with effective refractive indices as well as a rigorous coupled-wave analysis simulation. We experimentally show that SWS layers can work as homogeneous thin-film interference layers with effective refractive indices even if there are multiple SWS layers in a filter., Accepted for publication in J Infrared Milli Terahz Waves. The final publication will be available at Springer via http://dx.doi.org/10.1007/s10762-016-0328-z

We report the estimation of the heat dissipation on a levitating rotor over superconducting magnetic bearing operating below 10 K. The continuously rotating mechanism is one of key devices to support the rotation of a sapphire half wave plate (HWP) in a polarization modulator of a LiteBIRD satellite. Due to the system requirement, the HWP must be kept at a cryogenic temperature while it is spinning. In order to minimize the frictional energy loss, we employ a superconducting magnetic bearing (SMB) and AC synchronous motor, which enables a contactless rotational mechanism. While we can minimize the frictional heat loss, there exists an energy loss due to the magnetic friction. As a result, it is essential to build a thermal model an estimation of heat dissipation to this contactless rotor is important to predict how much the HWP temperature rises during its rotation. For an estimation of heat dissipation, we conduct an experiment in order to establish the thermal simulation model equivalent to the flight model in size. Each thermal contact conductance between the rotor and the cryogenic rotor holder is also estimated through the experiment data. From the data, we only can know the difference in the rotor temperature before and after the rotor rotation. We monitor the transient temperature profile of grippers after the rotor is gripped by them. The rotational time is related to the total heat dissipation on the rotor because the heat dissipation is attributed to two kinds of energy losses: a magnetic hysteresis and induced eddy currents on metal parts of the rotor. Finally, we make a comparison between the thermal model and the experimental result and estimate the allowable heat dissipation to keep the HWP temperature lower than 20K.

With the imminent launch of the JWST, the field of thermal-infrared (TIR) astronomy will enjoy a revolution. It is easy to imagine that all areas of infrared (IR) astronomy will be greatly advanced, but perhaps impossible to conceive of the new vistas that will be opened. To allow both follow-up JWST observations and a continuance of work started on the ground-based 8m’s, we continue to plan the science cases and instrument design for a TIR imager and spectrometer for early operation on the TMT. We present the current status of our science cases and the instrumentation plans, harnessing expertise across the TMT partnership. This instrument will be proposed by the MICHI team as a second-generation instrument in any upcoming calls for proposals., Ground-based and Airborne Instrumentation for Astronomy VII, June 10-15, 2018, Austin, USA, Series: Proceedings of SPIE; no. 10702

We present our design and development of a polarization modulator unit (PMU) for LiteBIRD space mission. LiteBIRD is a next generation cosmic microwave background (CMB) polarization satellite to measure the primordial B-mode. The science goal of LiteBIRD is to measure the tensor-to-scalar ratio with the sensitivity of δr < 10-3. The baseline design of LiteBIRD is to employ the PMU based on a continuous rotating half-wave plate (HWP) at a telescope aperture with a diameter of 400 mm. It is an essential for LiteBIRD to achieve the science goal because it significantly reduces detector noise and systematic uncertainties. The LiteBIRD PMU consists of a multi-layered sapphire as a broadband achromatic HWP and a mechanism to continuously rotate it at 88 rpm. The whole system is maintained at below 10K to minimize the thermal emission from the HWP. In this paper, we discuss the current development status of the broadband achromatic HWP and the cryogenic rotation mechanism.

The Mid-Infrared Multi-field Imager for gaZing at the UnKnown Universe (MIMIZUKU) is a mid-infrared camera and spectrograph developed as a first-generation instrument on the University of Tokyo Atacama Observatory (TAO) 6.5-m telescope. MIMIZUKU covers a wide wavelength range from 2 to 38 μm and has a unique optical device called Field Stacker which realizes accurate calibration of variable atmospheric transmittance with a few percent accuracy. By utilizing these capabilities, MIMIZUKU realizes mid-infrared long-term monitoring, which has not been challenged well. MIMIZUKU has three optical channels, called NIR, MIR-S, and MIR-L, to realize the wide wavelength coverage. The MIR-S channel, which covers 6.8–26 μm, has been completed by now. We are planning to perform engineering observations with this channel at the Subaru telescope before the completion of the TAO 6.5-m telescope. In this paper, we report the results of the laboratory tests to evaluate the optical and detector performances of the MIR-S channel. As a result, we confirmed a pixel scale of 0.12 arcsec/pix and a vignetting- free field of view of 2./0 1./8. The instrument throughputs for imaging modes are measured to be 20–30%. Those for N - and Q -band spectroscopy modes are 17 and 5%, respectively. As for the detector performance, we derived the quantum efficiency to be 40–50% in the mid-infrared wavelength region and measured the readout noise to be 3000–6000 electrons, which are larger than the spec value. It was found that this large readout noise degrades the sensitivity of MIMIZUKU by a factor of two.

著者人数: 13名, Accepted: 2018-01-15, 資料番号: SA1180027000

The Space Infrared Telescope for Cosmology and Astrophysics (SPICA) mission is a Japanese astronomical infrared satellite project optimized for mid' to far-infrared observatories. It will be launched at ambient temperature and cooled down on orbit by mechanical coolers on board with an efficient radiative cooling system, which allow us to have a 3.5m cooled (4.5K) telescope in space. SPICA will answer a number of important problems in present-day astronomy, ranging from the star-formation history of the universe to the formation of planets, owing to its high spatial resolution and unprecedented sensitivity in the mid- to far-infrared. The large aperture mirror for cryogenically use in space, however, demand a challenging development for the telescope system. A single aperture design of the primary mirror will be adopted for the SPICA telescope rather than deployable mirror designs to avoid further complexity and ensure the feasibility. The number of actuators for the primary mirror, if needed, will be minimized. Silicon carbide and carbon-filter reinforced silicon carbide are extensively investigated at present as the prime candidate materials for the SPICA primary mirror. This presentation reports the current status of the SPICA telescope system development.

SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is an astronomical mission optimized for mid-and far-infrared astronomy with a cryogenically cooled 3-m class telescope, envisioned for launch in early 2020s. Mid-infrared Camera and Spectrometer (MCS) is a focal plane instrument for SPICA with imaging and spectroscopic observing capabilities in the mid-infrared wavelength range of 5-38μm. MCS consists of two relay optical modules and following four scientific optical modules of WFC (Wide Field Camera; 5'x 5' field of view, f/11.7 and f/4.2 cameras), LRS (Low Resolution Spectrometer; 2'.5 long slits, prism dispersers, f/5.0 and f/1.7 cameras, spectral resolving power R ∼ 50-100), MRS (Mid Resolution Spectrometer; echelles, integral field units by image slicer, f/3.3 and f/1.9 cameras, R ∼ 1100-3000) and HRS (High Resolution Spectrometer; immersed echelles, f/6.0 and f/3.6 cameras, R ∼ 20000-30000). Here, we present optical design and expected optical performance of MCS. Most parts of MCS optics adopt off-axis reflective system for covering the wide wavelength range of 5-38μm without chromatic aberration and minimizing problems due to changes in shapes and refractive indices of materials from room temperature to cryogenic temperature. In order to achieve the high specification requirements of wide field of view, small F-number and large spectral resolving power with compact size, we employed the paraxial and aberration analysis of off-axial optical systems (Araki 2005 [1]) which is a design method using free-form surfaces for compact reflective optics such as head mount displays. As a result, we have successfully designed compact reflective optics for MCS with as-built performance of diffraction-limited image resolution.

This study describes the non-rotationally symmetric diamond turning (XZC turning) for producing large-size precision freeform mirror. This is a high speed machining method as compared with the traditional XYZ diamond milling or fly-cutting. Moreover, the application of this method is a key factor in the development of the ultra-precision light-weight freeform mirror for outer space use. This report introduces these cutting-edge approaches.

MIMIZUKU is the first-generation mid-infrared instrument for the university of Tokyo Atacama Observatory (TAO) 6.5-m telescope. MIMIZUKU provides imaging and spectroscopic monitoring capabilities in a wide wavelength range from 2 to 38 μm, including unique bands like 2.7-μm and 30-μm band. Recently, we decided to add spectroscopic functions, KL-band mode (λ= 2.1-4.0 μm; R =λ/Δλ ~ 210) and 2.7-μm band mode ( λ= 2.4-2.95 μm; R ~ 620), and continuous spectroscopic coverage from 2.1 to 26 μm is realized by this update. Their optical designing is completed, and fabrications of optical elements are ongoing. As recent progress, we also report the completion of the cryogenic system and optics. The cryogenic system has been updated by changing materials and structures of thermal links, and the temperatures of the optical bench and detector mounting stages finally achieved required temperatures. Their stability against instrument attitude is also confirmed through an inclination test. As for the optics, its gold-plated mirrors have been recovered from galvanic corrosion by refabrication and reconstruction. Enough image quality and stability are confirmed by room-temperature tests. MIMIZUKU is intended to be completed in this autumn, and commissioning at the Subaru telescope and scientific operations on the TAO telescope are planned in 2017 and around 2019, respectively. In this paper, these development activities and future prospects of MIMIZUKU are reported.

A cold chopper is a key device for next generation mid-infrared instruments such as TMT/MICHI. It should achieve fast and accurate position switching with a large chopping throw at cryogenic temperature. To satisfy the requirements, voice coil motors using superconducting MgB2 wire have been developed. We have made a first prototype of the VCM and carried out its performance measurements such as a transition temperature, transfer functions, and power dissipation in the laboratory. The results are almost consistent with the expectations and the calculations, but some show significant inconsistency. We have also made a next prototype which is small to fit the size of the MICHI chopper. This will be installed to a developing mid-infrared instrument MIMIZUKU and used for actual observations.

We have carried out a trial production of the large-format (n=11) image slicer unit for a possible future mid-infrared instrument on the TMT aiming to verify its technical feasibility. The key elements in our trial production are the monolithic large-format slice mirrors and the monolithic large-format pupil mirrors. The results of our trial production of those key elements based on the ultra high-precision cutting techniques and the assembly of the large-format image slicer unit are presented in this paper.

Accepted: 2016-02-10, 資料番号: SA1160066000

Using all-sky maps obtained from COBE/DIRBE at 3.5 and 4.9 um, we present a reanalysis of diffuse sky emissions such as zodiacal light (ZL), diffuse Galactic light (DGL), integrated starlight (ISL), and isotropic residual emission including the extragalactic background light (EBL). Our new analysis, which includes an improved estimate of ISL using the Wide-field Infrared Survey Explorer (WISE) data, enabled us to find the DGL signal in a direct linear correlation between diffuse near-infrared and 100 um emission at high Galactic latitudes (|b| > 35 degree). At 3.5um, the high-latitude DGL result is comparable to the low-latitude value derived from the previous DIRBE analysis. In comparison with models of the DGL spectrum assuming a size distribution of dust grains composed of amorphous silicate, graphite, and polycyclic aromatic hydrocarbon (PAH), the measured DGL values at 3.5 and 4.9 um constrain the mass fraction of PAH particles in the total dust species to be more than ~ 2%. This was consistent with the results of Spitzer/IRAC toward the lower Galactic latitude regions. The derived residual emission of 8.9 +/- 3.4 nW m^{-2} sr^{-1} at 3.5 um is marginally consistent with the level of integrated galaxy light and the EBL constraints from the gamma-ray observations. The residual emission at 4.9 um is not significantly detected due to the large uncertainty in the ZL subtraction, same as previous studies. Combined with our reanalysis of the DIRBE data at 1.25 and 2.2 um, the residual emission in the near-infrared exhibits the Rayleigh-Jeans spectrum., ApJ accepted

We present mid-infrared narrow-band images of the Orion BN/KL region, and N-band low-resolution spectra of IRc2 and the nearby radio source "I." The distributions of the silicate absorption strength and the color temperature have been revealed with a sub-arcsecond resolution. The detailed structure of the 7.8 micron/12.4 micron color temperature distribution was resolved in the vicinity of IRc2. A mid-infrared counterpart to source I has been detected as a large color temperature peak. The color temperature distribution shows an increasing gradient from IRc2 toward source I, and no dominant temperature peak is seen at IRc2. The spectral energy distribution of IRc2 could be fitted by a two-temperature component model, and the "warmer component" of the infrared emission from IRc2 could be reproduced by scattering of radiation from source I. IRc2 itself is not self-luminous, but is illuminated and heated by an embedded luminous young stellar object located at source I., 20 pages, 11 figures. Minor corrections had been done in the ver.2. Accepted for publication in PASJ

著者人数: 42名, Accepted: 2011-03-08, 資料番号: SA1003241000

We report a thermal analysis of a polarization modulator unit (PMU) for use in a space-borne cosmic microwave background (CMB) project. A measurement of the CMB polarization allows us to probe the physics of early universe, and that is the best method to test the cosmic inflation experimentally. One of the key instruments for this science is to use a halfwave plate (HWP) based polarization modulator. The HWP is required to rotate continuously at about 1 Hz below 10 K to minimize its own thermal emission to a detector system. The rotating HWP system at the cryogenic environment can be realized by using a superconducting magnetic bearing (SMB) without significant heat dissipation by mechanical friction. While the SMB achieves the smooth rotation due to the contactless bearing, an estimation of a levitating HWP temperature becomes a challenge. We manufactured a one-eighth scale prototype model of PMU and built a thermal model. We verified our thermal model with the experimental data. We forecasted the projected thermal performance of PMU for a full-scale model based on the thermal model. From this analysis, we discuss the design requirement toward constructing the full-scale model for use in a space environment such as a future CMB satellite mission, LiteBIRD.

著者人数：13名, Accepted: 2009-03-06, 資料番号: SA1000761000

We carried out high spatial resolution N-band imaging and spectroscopic observations of the planetary nebula BD +30 3639 with the Cooled Mid-Infrared Camera and Spectrometer (COMICS) mounted on the Subaru telescope. Mid-infrared images reveal a rectangle shell structure of the nebula extending over 4'', which is supposed to be formed by the superwind from the central star. We have detected [Ne II] 12.8 μm and the unidentified infrared (UIR) bands at 8.6 and 11.2 μm, together with the broad plateau emission in 11-13 μm. In addition, the spectra clearly indicate the presence of silicate absorption around 10 μm for the first time, which increases sharply at the outside of the shell. This can be attributed to silicate grains that were formed in the O-rich phase of the central star, which is now C-rich. The present data indicate that these silicate grains are located in a very thin shell, suggesting that BD +30 3639 underwent a short period (~100 yr) of a high mass-loss rate (~3 × 10−3 M☉ yr−1) at the last epoch of the O-rich phase. N-band spectra show that the distribution of [Ne II] is not clearly different from that of the UIR band and suggest that the UIR band carriers coexist with the ionized gas to some extent. This may be attributed to a slow destruction of the band carriers in the ionized region of the high electron density. The 10 μm continuum and the 11-13 μm plateau emission are dominant in the shell region, while the UIR 11.2 μm band becomes stronger in the outside of the shell, suggesting a change in the dust composition or the dust size distribution between the shell and the outside of the shell region. On the contrary, the peak wavelength of the UIR 11.2 μm band agrees with the class B spectrum, which is often seen in planetary nebulae, and does not change between the shell and the outside of the shell region. These facts suggest that the UIR band carriers are originally formed in the carbon-rich stellar wind and partially destroyed in the shell by shocks. The change of the UIR band spectrum from class B to A, which is generally seen in H II regions, should take place outside of the nebula.

We have carried out the mid-infrared slit spectroscopic observations of sources in the LMC and in NGC 6946 with AKARI/IRC. We investigate the properties of the UIR bands in terms of the star forming activities. We find systematically larger ratios of UIR bands in 6–9 μm to 11.2 μm band in active star forming regions than in the quiet regions. This behavior is consistent with the photo-ionization model of PAHs. Our results suggest that the ratios of UIR bands in 6–9 μm to 11.2 μm band can be used as more efficient and vigorous tools to measure the extent of on-going star formation in remote galaxies rather than just the presence or absence of the features themselves.

We present the 3.5 m SPace Infrared telescope for Cosmology and Astrophysics (SPICA) space telescope, the launch of which is schedule around year 2015 by the Japanese HII-A rocket, and specifically discuss its use in the context of direct observation of extra-solar planets. This actively cooled (4.5 K), single aperture telescope will operate in the mid and far infrared spectral regions, and up to submillimetric wavelengths (200 μm). The lowest spectral region (5 to 20 μm), where the spatial resolution is the most favorable, will be dedicated to high contrast imaging with coronagraphy. This article describes the SPICA coronagraph project in terms of science, as well as our efforts to study a suitable instrumental concept, compatible with the constraints of the telescope architecture. To cite this article: L. Abe et al., C. R. Physique 8 (2007).

著者人数: 12名, Accepted: 2015-05-04, 資料番号: SA1150076000

Accepted: 2014-12-18, 資料番号: SA1150330000

著者人数：13名, Accepted: 2006-05-15, 資料番号: SA1000388000

Accepted: 2006-04-11, 資料番号: SA1000390000

Faint standard stars in the mid-infrared region (less than a few hundred millijanskys at 9 μm) are required for the on-orbit calibration of the Infrared Camera (IRC) on board ASTRO-F because of its high sensitivity, as well as the small dynamic range. Mid-infrared low-resolution (λ/Δλ ~ 250) spectra of six faint K and M giant stars (70-180 mJy at 9 μm, K1.5-M0 III), which are located in the north ecliptic polar region and are thus suitable for calibrators for the IRC, are obtained by using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the Subaru telescope to test the faint-infrared standard-star network recently constructed for space-borne instruments. The spectra are directly calibrated relative to Vega (A0 V). The present results indicate that the spectra of the faint standard K-M0 giant stars show good agreement with those predicted in the standard network within 10% accuracy on average. The overall spectral shapes are also in agreement with the predictions. In particular, the observed SiO absorption feature in the 8 μm region matches well with the prediction for an M0 III star. The present observations directly connect a primary standard calibrator (Vega) to faint K giant calibrators of the network in the 10 μm region and validate several faint (~0.1 Jy) members of the standard-star network for the first time. Absolute calibrations are provided for five of the medium-band filters of the COMICS instrument in the 10 μm window.

Accepted: 2005-10-31, 資料番号: SA1000411000

SPICA is a cooled, single large-mirror space-telescope, which is under discussion as an succsesor of the ASTRO-F mission. One of the most ambitious challenges of the SPICA mission is the direct observations of exoplanets with a coronagraph instrument. We report cryogenic infrared optics to realize high quality wavefronts for the SPICA coronagraph.The SPICA satellite will be launched by an H-IIA rocket to Sun-Earth L2 Halo orbit early in the 2010s. The SPICA telescope is a Ritchey-Chretien optics with 3.5m diameter primary mirror, and cooled down to 4.5 K in orbit by radiation cooling and mechanical cryo-coolers. Main working wavelengths are 5–200 micron. Advantages of the SPICA coronagraph are the infrared wavelenths where the contrast between planets and central stars are smaller than the optical wavelengths, and that the cooled space telescope consists of monolithic mirrors.Development of light-weight cooled telescope is one of the most important tasks to realize SPICA. At the present, sintered SiC and carbon fiber reinforced SiC (C/SiC) composite are candidate materials for the mirrors, truss, and optical bench. For these materials, estimations and improvements of basic property and surface roughness in cryogenic temperatures have been carried out. Deformation of trial product mirrors by cooling is also examined.We are developing cryogenic deformable mirrors (DMs) because wave front accuracy of the SPICA telescope is 0.35 micron RMS, which is not enough for our coronagraphic instrument. For MEMS (Micro Electro Mechanical System) DM and some others, measurements of thermal deformation by cooling, electrical response, and heat generation are undergoing. Developments of a tip-tilt system for cryogenic usage started to cancel vibration caused by the cryo-coolers and other components and to realize a diffraction limit resolution. The first result of our binary mask coronagraph experiment is also shown.

We present mid-infrared imaging at 11.7 mu m for the quadruple lens systems, PG1115+080 and B1422+231, using the cooled mid-infrared camera and spectrometer (COMICS) attached on the Subaru telescope. These lensed QSOs are characterized by their anomalous optical and radio flux ratios as obtained for (A1, A2) images of PG1115+080 and (A, B, C) images of B1422+231, respectively, i.e., such flux ratios are hardly reproduced by lens models with smooth mass distribution. Our mid-infrared observations for these images have revealed that the mid-infrared flux ratio A2/A1 of PG1115+080 is virtually consistent with smooth lens models (but inconsistent with the optical flux ratio), whereas for B1422+231, the mid-infrared flux ratios among (A, B, C) are in good agreement with the radio flux ratios. We also identify a clear infrared bump in the spectral energy distributions of these QSOs, thereby indicating that the observed mid-infrared fluxes originate from a hot dust torus around a QSO nucleus. Based on the size estimate of the dust torus, we place limits on the mass of a substructure in these lens systems, causing the anomalous optical or radio flux ratios. For PG1115+080, the mass of a substructure inside an Einstein radius, M_E, is < 16 Msun, corresponding to either a star or a low-mass CDM subhalo having the mass of M_{100}^{SIS} < 2.2 * 10^4 Msun inside radius of 100 pc if modeled as a singular isothermal sphere (SIS). For B1422+231, we obtain M_E > 209 Msun, indicating that a CDM subhalo is more likely, having the mass of M_{100}^{SIS} > 7.4 * 10^4 Msun, 9 pages, 4 figures, 4 tables, ApJ in press

Accepted: 2004-10-18, 資料番号: SA1003389000

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.

We carried out imaging and long-slit spectroscopic observations of the Red Rectangle in the N -band using the 8.2-m SUBARU telescope. The resulting images reveal a central bright core and an extended nebula. The central core is slightly extended in the N -band. The core radius is estimated to be ~, which corresponds to 60 AU. The core spectrum is well modeled by blackbody emission with a temperature of 358 K. The estimated size and temperature are in good agreement with the predictions of recent dusty torus models. In the north/south nebula, unidentified infrared (UIR) emission features at 8.6 μ m and 11.2 μ m are prominently observed. At radii > they completely dominate the N -band spectra, suggesting that the nebula seen at N -band wavelengths is primarily brightened by the UIR-band emission, not by scattered light. We also detected shifts in the UIR-feature peaks with increasing distance from the center. These may be attributed to isotopic shifts due to the presence of in polycyclic aromatic hydrocarbons (PAH) like particles. In addition to the UIR emission, a broad feature at 11.27 μ m is seen at a distance of 0.3´´ on all sides of the nebula. We attribute this to crystalline silicate olivine grains around the central torus.

著者人数: 14名, Accepted: 2003-10-01, 資料番号: SA1003371000

Accepted: 2003-09-12, 資料番号: SA1004076000

We report the results of mid-infrared (7.8μm–13.2 μm) high-spatial resolution imaging and spectroscopic observations of the Galactic center region with the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the Subaru telescope. The images clearly show bright infrared sources and small structures in the diffuse emission. The spectra of all the observed positions show the 9.7 μm silicate absorption feature. After corrected for the empirically-derived extinction, the intrinsic spectra of the infrared sources show either strong silicate emission or absorption, while the intrinsic diffuse emission has a power-law type spectrum. This difference indicates a possibility of dust processing due to the interaction between the infrared sources and their surrounding medium or a different origin of the dust grains surrounding the sources from those in the diffuse region.

Accepted: 2002-10-14, 資料番号: SA1003358000