中川 貴雄

This paper presents a 610 MHz radio survey covering 1.94 deg around the North Ecliptic Pole (NEP), which includes parts of the (ADF-N) and Euclid, Deep Fields North. The median 5 sensitivity is 28 Jy beam, reaching as low as 19 Jy beam, with a synthesized beam of 3.6 arcsec 4.1 arcsec. The catalogue contains 1675 radio components, with 339 grouped into multicomponent sources and 284 'isolated' components likely part of double radio sources. Imaging, cataloguing, and source identification are presented, along with preliminary scientific results. From a non-statistical sub-set of 169 objects with multiwavelength AKARI and other detections, luminous infrared galaxies (LIRGs) represent 66 of the sample, ultra-luminous infrared galaxies (ULIRGs) 4, and sources with L < 10 30. In total, 56 of sources show some AGN presence, though only seven are AGN-dominated. ULIRGs require three times higher AGN contribution to produce high-quality SED fits compared to lower luminosity galaxies, and AGN presence increases with AGN fraction. The PAH mass fraction is not significant, although ULIRGs have about half the PAH strength of lower IR-luminosity galaxies. Higher luminosity galaxies show gas and stellar masses an order of magnitude larger, suggesting higher star formation rates. For LIRGs, AGN presence increases with redshift, indicating that part of the total luminosity could be contributed by AGN activity rather than star formation. Simple cross-matching revealed 13 ROSAT QSOs, 45 X-ray sources, and 61 sub-mm galaxies coincident with GMRT radio sources.

Determining the inner structure of the molecular torus around an active galactic nucleus is essential for understanding its formation mechanism. However, spatially resolving the torus is difficult because of its small size. To probe the clump conditions in the torus, we therefore perform the systematic velocity-decomposition analyses of the gaseous 12CO rovibrational absorption lines (v = 0 → 1, ΔJ = ±1) at λ ∼ 4.67 μm observed toward four (ultra)luminous infrared galaxies using the high-resolution (R ∼ 5000-10,000) spectroscopy from the Subaru Telescope. We find that each transition has two to five distinct velocity components with different line-of-sight (LOS) velocities (V LOS ∼ −240 to +100 km s−1) and dispersions (σ V ∼ 15-190 km s−1), i.e., the components (a), (b), ⋯, beginning with the broadest one in each target, indicating that the tori have clumpy structures. By assuming a hydrostatic disk ( σ V ∝ R rot − 0.5 ), we find that the tori has dynamic inner structures, with the innermost component (a) outflowing with velocity ∣V LOS∣ ∼ 160-240 km s−1, and the outer components (b) and (c) outflowing more slowly or infalling with ∣V LOS∣ ≲ 100 km s−1. In addition, we find that the innermost component (a) can be attributed to collisionally excited hot (≳530 K) and dense ( log ( n H 2 / cm − 3 ) ≳ 6 ) clumps, based on the level populations. Conversely, the outer component (b) can be attributed to cold (∼30-140 K) clumps radiatively excited by a far-infrared-to-submillimeter background with a brightness temperature higher than ∼20-400 K. These observational results demonstrate the clumpy and dynamic structure of tori in the presence of background radiation.

Abstract We investigate the physical origins of the Balmer decrement anomalies in GS-NDG-9422 and RXCJ2248-ID galaxies at z ∼ 6 whose Hα/Hβ values are significantly smaller than 2.7, the latter of which also shows anomalous Hγ/Hβ and Hδ/Hβ values beyond the errors. Because the anomalous Balmer decrements are not reproduced under the Case B recombination, we explore the nebulae with optical depths smaller and larger than the Case B recombination by physical modeling. We find two cases quantitatively explaining the anomalies: (1) density-bounded nebulae that are opaque only up to around Lyγ–Ly8 transitions and (2) ionization-bounded nebulae partly/fully surrounded by optically thick excited H i clouds. The case of (1) produces more Hβ photons via Lyγ absorption in the nebulae, requiring fine tuning in optical depth values, while this case helps ionizing photon escape for cosmic reionization. The case of (2) needs the optically thick excited Hi clouds with N ₂ ≃ 10¹²−10¹³ cm⁻², where N ₂ is the column density of the hydrogen atom with the principal quantum number of n = 2. Interestingly, the high N ₂ values qualitatively agree with the recent claims for GS-NDG-9422 with the strong nebular continuum requiring a number of 2s-state electrons and for RXCJ2248-ID with the dense ionized regions likely coexisting with the optically thick clouds. While the physical origin of the optically thick excited H i clouds is unclear, these results may suggest gas clouds with excessive collisional excitation caused by an amount of accretion and supernovae in the high-z galaxies.

Theoretical calculations predict that high-resolution spectroscopy of H2O gas lines in the mid-infrared region is the most promising method to observationally identify the snow-line, which has been proposed as the critical factor separating gas giants from solid planets in the planetary formation process. This requires the spectroscopic observations from space with R = λ/∆λ ≥ 30, 000. For this purpose, we propose a mid-infrared (10-18 µm) high-resolution spectrometer to be onboard the GREX-PLUS (Galaxy Reionization EXplorer and PLanetary Universe Spectrometer) mission. We are developing”immersion grating” spectroscopy technology for high-resolution spectroscopy in space. We have chosen CdZnTe as a candidate for the optical material. We report the current status of the development of the CdZnTe immersion grating, including evaluation of its optical properties (absorption coefficient and refractive index) at cryogenic temperatures, development of an anti-reflection coating with a moth-eye structure for wide-wavelength coverage, and verification of machinability for grating production. We plan to make a prototype spectrometer to demonstrate the capability of the immersion grating with ground-based observations in the N-band (λ = 8–13 µm) and beyond.

Extragalactic Background Light (EBL), the cumulative light from outside the galaxy, is a crucial observational target for understanding the history of the universe. We are developing a CubeSat; VERTECS (Visible Extragalactic background RadiaTion Exploration by CubeSat) with a 6U size (approximately 10 × 20 × 30 cm), equipped with Solar Array Wings (SAW). Our mission is to conduct extensive observations of the visible EBL. The satellite is designed to operate in a sun-synchronous orbit at an altitude of 500-680 km (approximately 15 orbits per day) and observe the EBL on the shadow side to avoid stray light from the Sun and Earth. To observe EBL, a high-performance CMOS sensor, attitude control devices, and high-speed communication equipment X-band are essential. We should note that these components these components consume a significant amount of power. Therefore, some strategic operational plans are necessary to operate this CubeSat within the limited power resources. In addition, VERTECS needs to meet its mission requirements, conducting 10 observations, 4 data downlinks, and 1 command uplink within a day. We have constructed some operational scenarios utilizing attitude control and SAW to meet these requirements, and we also constructed a power budget simulation for VERTECS. In this presentation, we describe how we plan to operate VERTECS utilizing the subsystems and the results of the power simulation during the operation.

The extragalactic background light (EBL) is the integrated emission from out of our Galaxy.Its observation is crucial for revealing the history of star-formation from the early universe to the present epoch. Visible Extragalactic background RadiaTion Exploration by CubeSat (VERTECS) is a 6U astronomical satellite to observe the EBL in visible wavelength from 0.4 µm to 0.8 µm. To observe the EBL, a telescope with 11 lenses and a high-performance CMOS sensor are equipped within 3U volume. The remaining 3U comprises the bus section mainly based on the bus design previously developed at Kyushu Institute of Technology. This paper describes the design and verification processes of the structure and thermal model of the satellite to fulfill the interface and mission requirements. From a mission perspective, the precise attitude and orbit control system unit is mounted on the same interface plate as the telescope to meet stringent pointing stability requirements during observations. The purpose of the stiff design of this interface plate is to minimize structural deformation. Furthermore, integrating multiple external antennas with relatively large X-band and S-band communication units require effective routing harness management. Static stress analysis is performed under the quasi-static loading condition. In addition, modal analysis is also conducted to fulfill the strength and stiffness requirements of the launcher. A series of mechanical environmental tests (shock, random, and sinusoidal vibrations) have been conducted to verify the design and analysis results. The results showed that designed model can fundamentally withstand the launch environment.

The Visible Extragalactic background RadiaTion Exploration by CubeSat (VERTECS) is designed for observing Extragalactic Background Light(EBL). VERTECS mission requires attitude control stability better than 10 arcsec (1σ) per minute, pointing accuracy better than 0.1 deg, and the slew rate faster than 1 deg per sec. We discuss the software-in-the-loop (SIL) attitude simulator simulation to verify whether the current Attitude Determination Control System (ADCS) design and the planned orbit can meet the requirements for EBL observations. We simulate the attitude control system with the simulation software, taking into account the attitude control commands, the parameters of the ADCS hardware, and the expected attitude disturbances in the assumed orbit. This simulation shows the sequence of attitude maneuvers needed to meet the requirement. The simulation results indicate that the current observation sequence is feasible.

We describe scientific o bjective a nd p roject s tatus o f a n a stronomical 6 U C ubeSat m ission V ERTECS (Visible Extragalactic background RadiaTion Exploration by CubeSat). The scientific g oal o f V ERTECS i s t o reveal the star-formation history along the evolution of the universe by measuring the extragalactic background light (EBL) in the visible wavelength. Earlier observations have shown that the near-infrared EBL is several times brighter than integrated light of individual galaxies. As candidates for the excess light, first-generation s tars in the early universe or low-redshift intra-halo light have been proposed. Since these objects are expected to show different e mission s pectra i n v isible w avelengths, m ulti-color v isible o bservations a re c rucial t o r eveal t he origin of the excess light. Since detection sensitivity of the EBL depends on the product of the telescope aperture and the field o f v iew, i t i s p ossible t o o bserve i t w ith a s mall b ut w ide-field te lescope sy stem th at ca n be mounted on the limited volume of CubeSat. In VERTECS mission, we develop a 6U CubeSat equipped with a 3U-sized telescope optimized for observation of the visible EBL. The bus system composed of onboard computer, electric power system, communication subsystem, and structure is based on heritage of series of CubeSats developed at Kyushu Institute of Technology in combination with high-precision attitude control subsystem and deployable solar array paddle required for the mission. The VERTECS mission was selected for JAXA-Small Satellite Rush Program (JAXA-SMASH Program), a new program that encourages universities, private companies and JAXA to collaborate to realize small satellite missions utilizing commercial small launch opportunities, and to diversify transportation services in Japan. We started the satellite development in December 2022 and plan to launch the satellite in FY2025.

The extragalactic background light (EBL) is the integrated emission from all objects outside of the Milky Way galaxy and is a crucial observational quantity in the broader study of the history of cosmic structures. In the near-infrared EBL, there have been measurements of an emission component several times brighter than the cumulative light from extragalactic galaxies. This unknown radiation component has led to proposals for candidate source objects, such as first stars and galactic halo brown dwarfs. These source objects exhibit distinct radiation spectra in the visible wavelength. The VERTECS (Visible Extragalactic background RadiaTion Exploration by CubeSat) project is focused on continuously observing the visible EBL using a wide-field small telescope on a 6U CubeSat. The primary characteristic of this telescope is its high-throughput (SΩ > 10−6 m2sr). The 3U-sized optical telescope onboard this satellite consists of a lens optics with a total field of view of 6◦ × 6◦, pixel field of view of 11” × 11”, a highly sensitive and low-noise detector module, and a baffle to eliminate stray light from the Sun and Earth. Additionally, color filters divide the wavelength range from 400 to 800 nm into four bands. Our observation strategy involves capturing 60-second exposure images while shifting the observed field by 3◦ increments and stacking the acquired images to perform photometry in the four bands. Thus far, most of the telescope design has met the required specifications, and the project is currently advancing towards the production of an engineering model. This project was selected in the JAXA-SMASH and is currently progressing in satellite development with a planned launch in the 2025 fiscal year. In this presentation, we will report on the strategy for observing the visible EBL, the progress in the development of the optical telescope, and the future plans.

Aims. In this work we examine how environment influences the merger fraction, from the low density field environment to higher density groups and clusters. We also study how the properties of a group or cluster, as well as the position of a galaxy in the group or cluster, influences the merger fraction. Methods. We identified galaxy groups and clusters in the North Ecliptic Pole using a friends-of-friends algorithm and the local density. Once identified, we determined the central galaxies, group radii, velocity dispersions, and group masses of these groups and clusters. Merging systems were identified with a neural network as well as visually. With these identifications and properties of groups and clusters and merging galaxy identifications, we examined how the merger fraction changes as the local density changes for all galaxies as well as how the merger fraction changes as the properties of the groups or clusters change. Results. We find that the merger fraction increases as local density increases and decreases as the velocity dispersion increases, as is often found in the literature. A decrease in merger fraction as the group mass increases is also found. We also find that groups with larger radii have higher merger fractions. The number of galaxies in a group does not influence the merger fraction. Conclusions. The decrease in merger fraction as group mass increases is a result of the link between group mass and velocity dispersion. Hence, this decrease in merger fraction with increasing mass is a result of the decrease of merger fraction with velocity dispersion. The increasing relation between group radii and merger fraction may be a result of larger groups having smaller velocity dispersion at a larger distance from the centre or larger groups hosting smaller, infalling groups with more mergers. However, we do not find evidence of smaller groups having higher merger fractions.

We introduce a novel model to spectroscopically constrain the mid-infrared (MIR) extinction/attenuation curve from 3-17 μm, using polycyclic aromatic hydrocarbon (PAH) emission drawn from an AKARI-Spitzer extragalactic cross-archival data set. Currently proposed MIR extinction curves vary significantly in their slopes toward the near-infrared, and the variation in the strengths and shapes of the 9.7 μm and 18 μm silicate absorption features make MIR spectral modeling and interpretation challenging, particularly for heavily obscured galaxies. By adopting the basic premise that PAH bands have relatively consistent intrinsic ratios within dusty starbursting galaxies, we can, for the first time, empirically determine the overall shape of the MIR attenuation curve by measuring the differential attenuation at specific PAH wavelengths. Our attenuation model shows PAH emission in most (ultra)luminous infrared galaxies is unambiguously subjected to attenuation, and we find strong evidence that PAH bands undergo differential attenuation as obscuration increases. Compared to preexisting results, the MIR attenuation curve derived from the model favors relatively gray continuum absorption from 3-8 μm and silicate features with intermediate strength at 9.7 μm but with stronger than typical 18 μm opacity.

This study focuses on optimizing the thermal performance of the Visible Extragalactic background RadiaTion Exploration by CubeSat (VERTECS), a 6U CubeSat with a 3U telescope for observing Extragalactic Background Light. Aside from dealing with satellite survivability in the space environment, the payload includes a CMOS sensor which requires operational temperatures of less than 0°C to minimize the noise due to temperature dependent dark current in observation data. The payload telescope lens optical system is designed to operate within a temperature range of -10°C to 35°C. The thermal analysis considers solar radiation, internal heat dissipation, and external factors in various orbital scenarios. The investigation identifies potential temperature fluctuations and proposes passive thermal control strategies, including enhanced coatings and radiators. By implementing tailored strategies, this research enhances the reliability and longevity of 6U CubeSat missions, advancing small satellite technology in space exploration and scientific research.

We’re developing an immersion grating made of CdZnTe designed for a high-dispersion mid-infrared spectrograph (10-18 µm, R = λ/∆λ ∼ 30, 000) to be onboard the next-generation infrared space telescope GREX-PLUS. The adoption of an immersion grating will reduce the spectrometer size to 1/n (1/n3 in volume, n: refractive index) compared to conventional diffraction g ratings. To d etermine t his a bsorption c oefficient acc urately, we nee d to take the effect o f m ultiple r eflection in to ac count th at de pend on th e re fractive in dex. Ho wever, th e accurate refractive index of CdZnTe (∆n < 10−4) at 10-18 µm below 20 K has not been measured yet. Therefore, we’re developing a measurement system of the refractive index at cryogenic temperatures in the mid-infrared range. We adopt the minimum deviation method in this system to measure the refractive index, measuring the apex and deviation angle of the prismatic sample of material to be measured. Here we give an overview of the measurement system, as well as preliminary results of the refractive index measurement.

We are developing an Immersion Grating (IG) made of CdZnTe which is designed for a high-dispersion mid-infrared spectrograph (10-18 µm, R = λ/∆λ ∼ 30, 000) to be onboard the next-generation infrared space telescope GREX-PLUS (Galaxy Reionization EXplorer and PLanetary Universe Spectrometer).1 The adoption of an IG will reduce the spectrometer size to 1/n in length (1/n3 in volume, n: refractive index) compared to conventional diffraction gratings. In order to determine the absorption coefficient of the high-resistivity CdZnTe, we developed a new measurement system for transmittance in 10-18 μm with cryogenic common-path double beam optics equipped with filament lamp source inside the vacuum chamber, which enables accurate determination of the transmittance at the cryogenic temperature by considering the effect of the multiple Fresnel reflection at the sample surface. By the new transmittance measurement system, the CdZnTe sample can be cooled down to ~6 K by employing cooled long wavelength band pass filter (λ > 7 µm) to attenuate the peak emission of the filament lamp (λ ~ 2 µm). In the present paper, we report the results of transmittance measurement with high precision (δτ~0.03%) by our new equipment for the high-resistivity CdZnTe, and the absorption coefficient α of high-resistivity CdZnTe. By applying the value of refractive index n at T > 5.7 K reported recently, α was estimated to be 0.00225 cm-1 and 0.00036 cm-1 at T~300 K and ~12 K, respectively at λ~10 µm in wavelength. In contrast to low-resistivity CdZnTe,7 the obtained values for α of high-resistivity CdZnTe have shown only slight temperature dependence, and the absorption coefficient values were smaller than the requirement: α<0.01 cm-1 for the IG material. The high-resistivity CdZnTe was likely to be a candidate material of IG for GREX-PLUS high-resolution spectrograph.

GREX-PLUS (Galaxy Reionization EXplorer and PLanetary Universe Spectrometer) is one of the three candidates of ISAS/JAXA’s Strategic L-class mission for the 2030s. The 1.2 m aperture, 50 K cryogenic space telescope with the wide-field camera (WFC) will provide the 1,260 square arcmin field-of-view for five photometric bands between 2 and 8 µm. The high resolution spectrometer (HRS) will observe the 10–18 µm with a wavelength resolution of 30,000. The GREX-PLUS WFC field-of-view is 130 times larger than that of the James Webb Space Telescope and similar to those of Euclid and Roman Space Telescope. Since these two survey missions are limited to the wavelength less than around 2 µm, GREX-PLUS will extend the wavelength coverage beyond 2 µm, providing versatile legacy imaging survey significantly improved from previous Spitzer imaging survey in the same wavelength range. The spectral resolution of the GREX-PLUS HRS is 10 times higher than that of the James Webb Space Telescope, opening a new window of the mid-infrared high-resolution spectroscopy from space. The main scientific themes are the galaxy formation and evolution and the planetary system formation and evolution. The GREX-PLUS WFC aims to detect the first generation of “bright” galaxies at redshift z > 15. The GREX-PLUS HRS aims to resolve the Kepler motion of water vapor molecules and identify the location of the water “snowline” in ∼ 100 proto-planetary disks. Both instruments will provide unique data sets for a broad range of scientific topics including galaxy mass assembly, origin of super massive blackholes, infrared background radiation, molecular spectroscopy in the interstellar medium, transit spectroscopy for exoplanet atmosphere, planetary atmosphere in the Solar system, and so on. This paper presents the status of the concept design of GREX-PLUS, including telescope system, WFC, HRS, cooling system, and spacecraft bus system.

We have developed a compact broadband infrared imaging Fourier transform spectrometer, referred to as the 2D FT-IR, employing common path wavefront division phase-shift interferometry. The system comprises a 3-reflector point-to-point optical setup with overlapping paths, incorporating two free-form mirrors and a pair of 20 mm high and 40 mm wide planar mirrors. Initially, we establish a one-dimensional multi-slit object plane with spacing tailored to match the FPA detector pixel size, effectively preventing destructive interference. Through precise optimization of the parameters of the two free-form mirrors (Mirror 1: 4th-order Zernike polynomial; Mirror 2: 6th-order Zernike polynomial), we achieve precise beam collimation, reflection through a phase shifter, and subsequent refocusing onto the FPA detector. Utilizing a commercial uncooled bolometer camera with a resolution of 640x480 pixels and a pixel size of 17μm, we attain optimal performance across the 4-20μm wavelength range, coupled with a generous 6mm diameter field of view. The spectrometer boasts a remarkable wavenumber resolution of 2.7 cm -1, with R (λ=4μm) ≈ 1000, alongside a spatial resolution of 34μm. All components seamlessly fit within a 170x150x80 mm vacuum frame. The 2D FT-IR enables the acquisition of spectral maps post-image capture and offers a broad measurement wavelength range of 4-20 μm. After completion of development, we plan to employ it to study the generation mechanisms of cryogenically frozen organic matter simulating Titan's haze and to measure the low-temperature continuous spectral transmittance and refractive index of the GREX-PLUS spectroscopic components. Additionally, due to its high vibration resistance and compact design, we intend to deploy it as a spectrometer for compact satellites developed by JAXA. Lastly, it will serve as a pivotal test instrument for the PLANETS telescope, facilitating the evaluation of the telescope's resistance to atmospheric disturbances.

We introduce Monte-Carlo-based non-local thermodynamic equilibrium (non-LTE) line radiative transfer calculations in the three-dimensional (3D) dust radiative transfer code SKIRT, which was originally set up as a dust radiative transfer code. By doing so, we developed a generic and powerful 3D radiative transfer code that can self-consistently generate spectra with molecular and atomic lines against the underlying continuum. We tested the accuracy of the non-LTE line radiative transfer module in the extended SKIRT code using standard benchmarks. We find excellent agreement between the S KIRT results, the published benchmark results, and the results obtained using the ray-tracing non-LTE line radiative transfer code MAGRITTE, which validates our implementation. We applied the extended SKIRT code on a 3D hydrodynamic simulation of a dusty active galactic nucleus (AGN) torus model and generated multiwavelength images with CO rotational-line spectra against the underlying dust continuum. We find that the low-J CO emission traces the geometrically thick molecular torus, whereas the higher-J CO lines originate from the gas with high kinetic temperature located in the innermost regions of the torus. Comparing the calculations with and without dust radiative transfer, we find that higher-J CO lines are slightly attenuated by the surrounding cold dust when seen edge-on. This shows that atomic and molecular lines can experience attenuation, an effect that is particularly important for transitions at mid- and near-infrared wavelengths. Therefore, our self-consistent dust and non-LTE line radiative transfer calculations can help the observational data from Herschel, ALMA, and JWST be interpreted.

In order to investigate the far-infrared excess detected from the western hot spot of the radio galaxy Pictor A with the Herschel observatory, submillimeter photometry is performed with the Atacama Compact Array (ACA) of the Atacama Large Millimeter/submillimeter Array at Band 8 with the reference frequency of 405 GHz. A submillimeter source is discovered at the radio peak of the hot spot. Because the 405 GHz flux density of the source, 80.7 ± 3.1 mJy, agrees with the extrapolation of the synchrotron radio spectrum, the far-infrared excess is suggested to exhibit no major contribution at the ACA band. In contrast, by subtracting the power-law spectrum tightly constrained by the radio and ACA data, the significance of the excess in the Herschel band is well confirmed. No diffuse submillimeter emission is detected within the ACA field of view, and thus, the excess is ascribed to the western hot spot itself. In comparison to the previous estimate based on the Herschel data, the relative contribution of the far-infrared excess is reduced by a factor of ∼1.5. The spectrum of the excess below the far-infrared band is determined to be harder than that of the diffusive shock acceleration. This strengthens the previous interpretation that the excess originates via the magnetic turbulence in the substructures within the hot spot. The ACA data are utilized to evaluate the magnetic field strength of the excess and of diffuse radio structure associated with the hot spot.

We investigated the inner buried nucleus of a nearby luminous infrared galaxy, NGC 4418, using high-resolution spectroscopy of fundamental carbon monoxide (CO) rovibrational absorptions around 4.67 μm for the first time. This method allowed us to examine the physical and kinematical properties in the hot inner region of this nucleus. We detected a series of both very deep (partly saturated) 12CO and moderately deep (optically thin) 13CO absorption lines and inferred a large column density (N H2 = (5 ± 3) × 1023 cm−2 in front of the 5 μm photosphere) of warm (T ex ≃ 170 K) molecular gas by assuming an isothermal plane-parallel slab illuminated by a compact background mid-infrared-emitting source. We modeled that the warm CO absorber almost covers the central heating source and that it is an inner layer around the 5 μm photosphere (at r = several parsecs) of a compact shroud of gas and dust (d ∼ 100 pc). The width of the absorption lines (110 km s−1) and their small deviation from the systemic velocity (<10 km s−1) are consistent with a warm and turbulent layer with little bulk motion in the radial direction.

Abstract The Subaru telescope is currently performing a strategic program (SSP) using the high-precision near-infrared (NIR) spectrometer IRD to search for exoplanets around nearby mid/late M dwarfs via radial velocity (RV) monitoring. As part of the observing strategy for the exoplanet survey, signatures of massive companions such as RV trends are used to reduce the priority of those stars. However, this RV information remains useful for studying the stellar multiplicity of nearby M dwarfs. To search for companions around such “deprioritized” M dwarfs, we observed 14 IRD-SSP targets using Keck/NIRC2 with pyramid wave-front sensing at NIR wavelengths, leading to high sensitivity to substellar-mass companions within a few arcseconds. We detected two new companions (LSPM J1002+1459 B and LSPM J2204+1505 B) and two new candidates that are likely companions (LSPM J0825+6902 B and LSPM J1645+0444 B), as well as one known companion. Including two known companions resolved by the IRD fiber injection module camera, we detected seven (four new) companions at projected separations between ∼2 and 20 au in total. A comparison of the colors with the spectral library suggests that LSPM J2204+1505 B and LSPM J0825+6902 B are located at the boundary between late M and early L spectral types. Our deep high-contrast imaging for targets where no bright companions were resolved did not reveal any additional companion candidates. The NIRC2 detection limits could constrain potential substellar-mass companions (∼10–75 M_Jup) at 10 au or further. The failure with Keck/NIRC2 around the IRD-SSP stars having significant RV trends makes these objects promising targets for further RV monitoring or deeper imaging with the James Webb Space Telescope to search for smaller-mass companions below the NIRC2 detection limits.

We investigate the variation in the mid-infrared spectral energy distributions of 373 low-redshift (z < 0.4) star-forming galaxies, which reflects a variety of polycyclic aromatic hydrocarbon (PAH) emission features. The relative strength of PAH emission is parameterized as q PAH, which is defined as the mass fraction of PAH particles in the total dust mass. With the aid of continuous mid-infrared photometric data points covering 7-24 μm and far-infrared flux densities, q PAH values are derived through spectral energy distribution fitting. The correlation between q PAH and other physical properties of galaxies, i.e., gas-phase metallicity (12 + log (O / H )), stellar mass, and specific star-formation rate (sSFR) are explored. As in previous studies, q PAH values of galaxies with high metallicity are found to be higher than those with low metallicity. The strength of PAH emission is also positively correlated with the stellar mass and negatively correlated with the sSFR. The correlation between q PAH and each parameter still exists even after the other two parameters are fixed. In addition to the PAH strength, the application of metallicity-dependent gas-to-dust mass ratio appears to work well to estimate gas mass that matches the observed relationship between molecular gas and physical parameters. The result obtained will be used to calibrate the observed PAH luminosity-total infrared luminosity relation, based on the variation of MIR-FIR SED, which is used in the estimation of hidden star formation.

Space-qualified Joule Thomson coolers with significant cooling power below 5K enable a variety of missions, which include large infrared space telescopes, superconducting detectors for astrophysics, and quantum applications. In JAXA, a 4K-class Joule–Thomson cryocooler (4K-JT) and a 1K-class Joule–Thomson cryocooler (1K-JT) have been developed with the required cooling power of 40mW at 4.5K and 10mW at 1.7K respectively, for upcoming next-generation space missions. This paper reports the results of cooling performance tests of these JT coolers with straight heat exchangers. A straight heat exchanger is desirable in several space science missions, including the Space Infrared Telescope for Cosmology and Astrophysics (SPICA), while the coiled type of heat exchanger was used in past missions. The effectiveness of the heat exchanger is strongly affected by its shape and length, and the effectiveness significantly influences the cooling power and the cooling efficiency of the Joule–Thomson cooler. This study designed, fabricated and measured several types of heat exchanger test models. The effect of gravity and the thermal environment on cooling performance are also reported.

We report the near-infrared radial velocity (RV) discovery of a super-Earth planet on a 10.77 d orbit around the M4.5 dwarf Ross 508 (J(mag) = 9.1). Using precision RVs from the Subaru Telescope IRD (InfraRed Doppler) instrument, we derive a semi-amplitude of 3.92(-0.58)(+0.60) m s(-1), corresponding to a planet with a minimum mass msin i = 4.00(-0.55)(+0.53) M-circle plus. We find no evidence of significant signals at the detected period in spectroscopic stellar activity indicators or MEarth photometry. The planet, Ross 508 b, has a semi-major axis of 0.05366(-0.00049)(+0.00056) au. This gives an orbit-averaged insolation of approximate to 1.4 times the Earth's value, placing Ross 508 b near the inner edge of its star's habitable zone. We have explored the possibility that the planet has a high eccentricity and its host is accompanied by an additional unconfirmed companion on a wide orbit. Our discovery demonstrates that the near-infrared RV search can play a crucial role in finding a low-mass planet around cool M dwarfs like Ross 508.

Abstract A recent hydrodynamic model, the radiation-driven fountain model (Wada et al. 2016), presented a dynamical picture that active galactic nuclei (AGNs) tori sustain their geometrical thickness by gas circulation around AGNs, and previous papers have confirmed that this picture is consistent with multiwavelength observations of nearby Seyfert galaxies. Recent near-infrared observations implied that CO rovibrational absorption lines (ΔJ = ± 1, v = 0 − 1, λ ∼ 4.7 μm) could probe the physical properties of the inside tori. However, the origin of the CO absorption lines has been under debate. In this paper, we investigate the origin of the absorption lines and conditions for detecting them by performing line radiative transfer calculations based on the radiation-driven fountain model. We find that CO rovibrational absorption lines are detected at inclination angles θ_obs = 50°–80°. At the inclination angle θ_obs = 77°, we observe multi-velocity components: inflow (v_LOS = 30 km s⁻¹), systemic (v_LOS = 0 km s⁻¹), and outflows (v_LOS = −75, − 95, and −105 km s⁻¹). The inflow and outflow components (v_LOS = 30 and −95 km s⁻¹) are collisionally excited at the excitation temperatures of 186 and 380 K up to J = 12 and 4, respectively. The inflow and outflow components originate from the accreting gas on the equatorial plane at 1.5 pc from the AGN center and the outflowing gas driven by AGN radiation pressure at 1.0 pc, respectively. These results suggest that CO rovibrational absorption lines can provide us with the velocities and kinetic temperatures of the inflow and outflow in the inner few parsec region of AGN tori, and the observations can probe the gas circulation inside the tori.

We performed wave-optics-based numerical simulations at mid-infrared wavelengths to investigate how the presence or absence of entrance slits and optical aberrations affect the spectral resolving power R of a compact, high-spectral-resolving-power spectrometer containing an immersion-echelle grating. We tested three cases of telescope aberration (aberration-free, astigmatism, and spherical aberration), assuming the aberration budget of the Space Infrared Telescope for Cosmology and Astrophysics, which has a 20 μm wavelength diffraction limit. In cases with a slit, we found that the value of R at around 10 to 20 μm is approximately independent of the assumed aberrations, which is significantly different from the prediction of geometrical optics. Our results also indicate that diffraction from the slit improves R by enlarging the effective illuminated area on the grating window and that this improvement decreases at short wavelengths. For the slit-less cases, we found that the impact of aberrations on R can be roughly estimated using the Strehl ratio.

The ultraluminous infrared galaxy IRAS 17208$-$0014 is a late-stage merger that hosts a buried active galactic nucleus (AGN). To investigate its nuclear structure, we performed high spatial resolution ($\sim0.\!\!^{\prime\prime}04\sim32\,\mathrm{pc}$) Atacama Large Millimeter/submillimeter Array (ALMA) observations in Band 9 ($\sim$450\,\micron\ or $\sim$660\,GHz), along with near-infrared AKARI spectroscopy in 2.5--5.0\,\micron. The Band 9 dust continuum peaks at the AGN location, and toward this position CO($J$=6--5) and CS($J$=14--13) are detected in absorption. Comparison with non-local thermal equilibrium calculations indicates that, within the central beam ($r\sim20\,\mathrm{pc}$), there exists a concentrated component that is dense ($10^7\,\mathrm{cm}^{-2}$) and warm ($>$200\,K) and has a large column density ($N_\mathrm{H_2}>10^{23}\,\mathrm{cm}^{-2}$). The AKARI spectrum shows deep and broad CO ro-vibrational absorption at 4.67\,\micron. Its band profile is well reproduced with a similarly dense and large column but hotter ($\sim$1000\,K) gas. The region observed through absorption in the near-infrared is highly likely in the nuclear direction, as in the sub-millimeter, but with a narrower beam including a region closer to the nucleus. The central component is considered to possess a hot structure where vibrationally excited HCN emission originates. The most plausible heating source for the gas is X-rays from the AGN. The AKARI spectrum does not show other AGN signs in 2.5--4\,\micron, but this absence may be usual for AGNs buried in a hot mid-infrared core. Besides, based on our ALMA observations, we relate various nuclear structures of IRAS 17208$-$0014 that have been proposed in the literature.

Detailed chemical analyses of M dwarfs are scarce but necessary to constrain the formation environment and internal structure of planets being found around them. We present elemental abundances of 13 M dwarfs (2900 < T (eff) < 3500 K) observed in the Subaru/IRD planet search project. They are mid- to late-M dwarfs whose abundance of individual elements has not been well studied. We use the high-resolution (similar to 70,000) near-infrared (970-1750 nm) spectra to measure the abundances of Na, Mg, Si, K, Ca, Ti, V, Cr, Mn, Fe, and Sr by the line-by-line analysis based on model atmospheres, with typical errors ranging from 0.2 dex for [Fe/H] to 0.3-0.4 dex for other [X/H]. We measure radial velocities from the spectra and combine them with Gaia astrometry to calculate the Galactocentric space velocities UVW. The resulting [Fe/H] values agree with previous estimates based on medium-resolution K-band spectroscopy, showing a wide distribution of metallicity (-0.6 < [Fe/H] < +0.4). The abundance ratios of individual elements [X/Fe] are generally aligned with the solar values in all targets. While the [X/Fe] distributions are comparable to those of nearby FGK stars, most of which belong to the thin-disk population, the most metal-poor object, GJ 699, could be a thick-disk star. The UVW velocities also support this. The results raise the prospect that near-infrared spectra of M dwarfs obtained in the planet search projects can be used to grasp the trend of elemental abundances and the Galactic stellar population of nearby M dwarfs.

To reveal the causes of infrared absorption in the wavelength region between electronic and lattice absorptions, we measured the temperature dependence of the absorption coefficient of p-type low-resistivity (similar to 10(2) Omega cm) CdZnTe crystals. We measured the absorption coefficients of CdZnTe crystals in four wavelength bands (lambda = 6.45, 10.6, 11.6, 15.1 mu m) over the temperature range of T = 8.6-300 K with an originally developed system. The CdZnTe absorption coefficient was measured to be alpha = 0.3-0.5 cm(-1) at T = 300 K and alpha = 0.4-0.9 cm(-1) at T = 8.6 K in the investigated wavelength range. With an absorption model based on transitions of free holes and holes trapped at an acceptor level, we conclude that the absorption due to free holes at T = 150-300 K and that due to trapped-holes at T < 50 K are dominant absorption causes in CdZnTe. We also discuss a method to predict the CdZnTe absorption coefficient at cryogenic temperature based on the room-temperature resistivity.

The application of superelastic alloys to microvibration isolators for a spacecraft was studied. The superelastic alloy in this study is characterized by a wide hysteresis loop in the stress-strain curve, which dissipates a large amount of energy even with a slight change in stress. Prototype struts with damping mechanisms utilizing such characteristics were developed, and an isolation system consisting of the damping struts was investigated. The isolation system was designed to satisfy the requirements of the Space Infrared Telescope for Cosmology and Astrophysics (SPICA), which has several mechanical cryocoolers to cool down the entire telescope to cryogenic temperature. Since the vibrations generated by the cryocoolers can be transmitted to the telescope and deteriorate the pointing stability, SPICA is designed to integrate all cryocoolers into cooler plates and isolate the plates from vibrations with the isolation system. The simulation method to design the isolation system was developed and validated by comparing the estimation with the test results of a bipod with a pair of the damping struts.

Dust and gas in protoplanetary disks dissipate as central stars evolve. In order to estimate the dust dissipation timescales in the protoplanetary disks, we stacked the WISE 12 and 22, and the AKARI 90 mu m survey images of known T Tauri stars and derived the average fluxes, well below the survey flux limit in the 90 mu m band. We classified 4783 T Tauri stars into three age groups, which are young (<2 Myr), mid-age (2-6 Myr), and old (>6 Myr) groups, and stacked the WISE 12 and 22 and the AKARI 90 mu m images in each group. The photometry of the stacked image shows the flux decay timescales of 1.4 +/- 0.2, 1.38 +/- 0.05, and 1.4(-0.5)(+0.6) Myr in the 12, 22, and 90 mu m bands, respectively. In optically thin disks with one-solar luminosity central stars, the 12 and 22 mu m fluxes are attributed to the emission from the intermediate (similar to 1 au) region and the 90 mu m flux corresponds to that from the outer (similar to 10 au) region in the disk. We hence conclude that the dust dissipation timescale is tau(med,dust) similar to 1.4 Myr in the intermediate disks and is tau(outer.dust) = 1.4(-0.5)(+0.6) Myr in the outer disks. The dust-dissipation time difference between the outer and intermediate disks is Delta tau(dust) = tau(outer.dust) - tau(med,dust) = 0.0(-0.5)(+0.6) Myr, indicating that the dust in the intermediate and outer disks dissipates on almost the same timescale.

We conducted systematic observations of the H i Br alpha (4.05 mu m) and Br beta (2.63 mu m) lines in 52 nearby (z < 0.3) ultraluminous infrared galaxies (ULIRGs) with AKARI. Among 33 ULIRGs wherein the lines are detected, 3 galaxies show anomalous Br beta/Br alpha line ratios (similar to 1.0), which are significantly higher than those for case B (0.565). Our observations also show that ULIRGs have a tendency to exhibit higher Br beta/Br alpha line ratios than those observed in Galactic H ii regions. The high Br beta/Br alpha line ratios cannot be explained by a combination of dust extinction and case B since dust extinction reduces the ratio. We explore possible causes for the high Br beta/Br alpha line ratios and show that the observed ratios can be explained by a combination of an optically thick Br alpha line and an optically thin Br beta line. We simulated the H ii regions in ULIRGs with the Cloudy code, and our results show that the high Br beta/Br alpha line ratios can be explained by high-density conditions, wherein the Br alpha line becomes optically thick. To achieve a column density large enough to make the Br alpha line optically thick within a single H ii region, the gas density must be as high as n similar to 10(8) cm(-3). We therefore propose an ensemble of H ii regions, in each of which the Br alpha line is optically thick, to explain the high Br beta/Br alpha line ratio.

In this era of spatially resolved observations of planet-forming disks with Atacama Large Millimeter Array (ALMA) and large ground-based telescopes such as the Very Large Telescope (VLT), Keck, and Subaru, we still lack statistically relevant information on the quantity and composition of the material that is building the planets, such as the total disk gas mass, the ice content of dust, and the state of water in planetesimals. SPace Infrared telescope for Cosmology and Astrophysics (SPICA) is an infrared space mission concept developed jointly by Japan Aerospace Exploration Agency (JAXA) and European Space Agency (ESA) to address these questions. The key unique capabilities of SPICA that enable this research are (1) the wide spectral coverage, (2) the high line detection sensitivity of with in the far-IR (SAFARI), and with in the mid-IR (SPICA Mid-infrared Instrument (SMI), spectrally resolving line profiles), (3) the high far-IR continuum sensitivity of 0.45 mJy (SAFARI), and (4) the observing efficiency for point source surveys. This paper details how mid- to far-IR infrared spectra will be unique in measuring the gas masses and water/ice content of disks and how these quantities evolve during the planet-forming period. These observations will clarify the crucial transition when disks exhaust their primordial gas and further planet formation requires secondary gas produced from planetesimals. The high spectral resolution mid-IR is also unique for determining the location of the snowline dividing the rocky and icy mass reservoirs within the disk and how the divide evolves during the build-up of planetary systems. Infrared spectroscopy (mid- to far-IR) of key solid-state bands is crucial for assessing whether extensive radial mixing, which is part of our Solar System history, is a general process occurring in most planetary systems and whether extrasolar planetesimals are similar to our Solar System comets/asteroids. We demonstrate that the SPICA mission concept would allow us to achieve the above ambitious science goals through large surveys of several hundred disks within months of observing time.

Understanding the inner structure of the clumpy molecular torus surrounding the active galactic nucleus is essential in revealing the forming mechanism However, spatially resolving the torus is difficult because of its size of a few parsecs. Thus, to probe the clump conditions in the torus, we performed the velocity decomposition of the CO rovibrational absorption lines (Delta nu = 0 -> 1, Delta J= +/- 1) at lambda similar to 4.67 mu m observed toward an ultraluminous infrared galaxy IRAS 08572+3915 NW with the high-resolution spectroscopy (R similar to 10,000) of Subaru Telescope. Consequently, we found that each transition had two outflowing components, i.e., (a) and (b), both at approximately similar to-160 km s(-1), but with broad and narrow widths, and an inflowing component, i.e., (c), at approximately similar to+100 km s(-1), which were attributed to the torus. The ratios of the velocity dispersions of each component led to those of the rotating radii around the black hole of R-rot,R-a: R-rot,R-b: R-rot,R-c approximate to 1: 5: 17, indicating the torus where clumps are outflowing in the inner regions and inflowing in the outer regions if a hydrostatic disk with sigma(V) proportional to R-rot(-0.5) is assumed. Based on the kinetic temperature of components (a) and (b) of similar to 720 and similar to 25 K, respectively, estimated from the level population, the temperature gradient is T-kin proportional to R-rot(-)2.1. Magnetohydrodynamic models with large density fluctuations of two orders of magnitude or more are necessary to reproduce this gradient.

Aims. We investigate the properties of [C II] 158 μm emission of RCW 36 in a dense filamentary cloud. Methods. [C II] observations of RCW 36, covering an area of ~30′ × 30′, were carried out with a Fabry-Pérot spectrometer on board a 100-cm balloon-borne far-infrared (IR) telescope with an angular resolution of 90′′. Using AKARI and Herschel images, we compared the spatial distribution of the [C II] intensity with the emission from the large grains and polycyclic aromatic hydrocarbon (PAH). Results. The [C II] emission is in good spatial agreement with shell-like structures of a bipolar lobe observed in IR images, which extend along the direction perpendicular to the direction of cold dense filament. We found that the [C II]-160 μm relation for RCW 36 shows a higher brightness ratio of [C II]/160 μm than that for RCW 38, while the [C II]-9 μm relation for RCW 36 is in good agreement with that for RCW 38. Conclusions. Via a spectral decomposition analysis on a pixel-by-pixel basis using IR images, the [C II] emission is spatially well correlated with PAH and cold dust emissions. This means that the observed [C II] emission predominantly comes from photo-dissociation regions. Moreover, the L[C II]LFIR ratio shows large variation (10-2-10-3), as compared with the L[C II]/LPAH ratio. In view of the observed tight correlation between L[C II]LFIR and the optical depth at λ = 160 μm, the large variation in L[C II]LFIR can be simply explained by the geometrical effect, that is, LFIR has contributions from the entire dust-cloud column along the line of sight, while L[C II] has contributions from far-UV illuminated cloud surfaces. Based on the picture of the geometry effect, the enhanced brightness ratio of [C II]/160 μm is attributed to the difference in gas structures where massive stars are formed: filamentary (RCW 36) and clumpy (RCW 38) molecular clouds; thus suggesting that RCW 36 is dominated by far-UV illuminated cloud surfaces, as compared with RCW 38.

The 4K Joule-Thomson (JT) cryocooler is a key cryogenic component for future astronomy missions such as ATHENA and LiteBIRD. It was originally developed for SMILES (2009) and upgraded for ASTRO-H/SXS (2016) and SPICA. The 20K two-stage Stirling cryocooler developed for AKARI (2006) was also upgraded and used as a precooler. The operational life is a critical factor in planning long-term missions. An engineering model of the 4KJT cryocooler was built for continuous operation to verify its lifetime. Testing was done from 2010 to 2019 and successful three-year operation was demonstrated with an extended operation; this was beyond the design specification. This paper describes the overall history of the lifetime test of the 4K-JT cryocooler and an evaluation of the end-of-life cooling performance and performance changes during long-term operation.

In the framework of the ESA X-ray mission ATHENA, scheduled for launch in 2030, an ESA Core Technology Program (CTP) was started in 2016 to build a flight like cryostat demonstrator in parallel with the phase A studies of the ATHENA/X-IFU instrument. As part of this CTP, called the Detector Cooling System (DCS), design, manufacturing and test of a cryostat including existing space coolers will be done. In addition to the validation of thermal performance, a Focal Plan Assembly (FPA) demonstrator using Transition Edge Sensors (TES) detector technology will be also integrated and its performance characterized versus the environment provided by the cryostat. This is a unique opportunity to validate many crucial issues of the cryogenic part of such a sensitive instrument. A dedicated activity within this CTP-DCS is the demonstration of the 300 K–50 mK cooling chain in a Ground System Equipment (GSE) cryostat. The studies are focused on the operation of the space coolers, which is made possible by the use of a ground cooler for cooling cryogenic shields and mechanical supports. This test program is also the opportunity to validate the operation of the cryochain with respect to various requirements, such as time constant and temperature stabilities. This would bring us valuable inputs to integrate the cryochain in DCS cryostat, X-IFU studies, SPICA and LiteBIRD missions. This paper is focused on the operation of the full 300 K–50 mK cryochain. In particular, the recycling options of the sub Kelvin cooler (sorption cooler + an ADR) versus the capability of 4 K and 2 K JT coolers are described. Results on the JT parameters validation campaign are summarized and eventually the results of the coupled test with sub Kelvin cooler will be presented and discussed.

In published article, we did not take into account that the [N II] λλ6548, 6584 A lines are within the wavelength range of the IPHAS Hα filter. The [N II] to Hα line ratio observed for the H II regions in our Galaxy is not negligible ([N II]/Hα ≈ 0.25; Haffner et al. 2009). Therefore, in this erratum, we correct the Hα fluxes of the H II regions (or candidates) estimated in the published article (Figur Presented) by eliminating the [N II] contributions to the IPHAS Hα. Although there is the radial abundance gradient of N/H in our Galaxy (Esteban & García-Rojas 2018), the directions of the H II regions in this study (ℓ = 96°-116°) are not largely different from those of Haffner et al. (2009) (ℓ = 130°-160°). So, we assumed the line ratio of [N II]/Hα ≈ 0.25 for the correction. Additionally, according to Barentsen et al. (2014), the Hα magnitude for Vega is conventionally set to 0.03 mag. Therefore, we adopted the Vega Hα magnitude of 0.03 mag, instead of 0 mag in the published article, for the calculations of the IPHAS Hα fluxes, though this effect is not large compared to the effects of the other changes. In this erratum, we also apply the recently updated calibration factors for the MIPAPS data (27.8 ± 2.0 mJy (ADU s-1)-1 for PAAL and 17.2 ± 1.2 mJy (ADU s-1)-1 for PAAC; I.-J. Kim et al. 2020, in preparation) to the measurements of the Paα fluxes. In the published article, we used the calibration factors of 23.7 ± 0.1 and 14.6 ± 0.1 mJy (ADU s-1)-1, respectively.

Two-stage Stirling cryocoolers (2ST cooler) produced by Sumitomo Heavy Industries, Ltd. have been launched into orbit on three satellites: the “AKARI (ASTRO-F)” infrared astronomical satellite, JEM/SMILES on ISS, and the “HITOMI (ASTRO-H)” X-ray astronomical satellite. A 2ST cooler compressor has a linear-ball-bearing system as a piston-supporting structure. The linear ball bearing system is a key components to realize a lower drive frequency (15 Hz), a long piston stroke (30 mm). Its typical cooling power is 200 mW at 20 K for the second stage and 1000 mW at 100 K for the first stage, with 90 W electrical input power. During the test of the “HITOMI” engineering model, the energy resolution of the detector was found to be degraded when cryocoolers were in operation. After investigation, it was found that micro vibration from 2STs caused the degradation. The continuum in the vibration spectrum propagated into sub-Kelvin region and generated thermal noise. The continuum has origin in linear ball bearing in the compressor. In the case of “HITOMI”, vibration isolators were introduced to resolve this issue. For future mission, we are required to reduce microvibration of cryocooler itself. Therefore, the piston support mechanism in the compressor was modified from linear ball bearings to triangle shape flexure springs in order to reduce the continuum in vibration spectrum. In order to achieve a long piston stroke (±15 mm), the generated stress could be reduced to 400 MPa (Less than 1/2 of fatigue limit) or less even when the shape of the triangle shape flexure spring was devised and displaced by 15 mm. The typical vibration level has been reduced to 1 × 10 Nrms / Hz or less at a frequency of 200 Hz or less and 1/10 times or less at 200–600 Hz than that of a compressor with a linear ball bearing system. The cooling power is kept to 260 mW at 20 K, with 90 W electrical input power. This low vibration cooler is expected to be an improved cryogenic system for use in future projects with sub-Kelvin detectors. −5 2

In space science missions that uses cryogen-free mechanical cooler systems to cool the low temperature telescope and detectors, a cooling time from room temperature to low temperature should be considered in the required mission life time, because of a limited cooling power of mechanical cooler. For instance, in the Space Infrared Telescope for Cosmology and Astrophysics (SPICA), the 4K-class Joule Thomson cooler (4K-JT) and the 1K-class Joule Thomson cooler (1K-JT) are being considered to cool a 2.5 m telescope and provide a 1–4 K environment for scientific instruments. The cooling capability of these JT coolers, below 20 K and even lower than 5 K, is critical for initial cooling. The 4K-JT cooling from precooling to operating temperatures under the heat input was measured and confirmed that the 4K-JT has enough cooling power to cool with these heat load. The 1K-JT cool down measurement with heater was also performed. These results enabled us to estimate the cool down time for the heat capacity provided by the telescope and scientific instruments assumed in SPICA, LiteBIRD and the ESA X-ray mission ATHENA.

We analyzed the young (2.8 Myr-old) binary system FS Tau A using near-infrared (H-band) high-contrast polarimetry data from Subaru/HiCIAO and submillimeter CO (J = 2-1) line emission data from Atacama Large Millimeter/submillimeter Array (ALMA). Both the near-infrared and submillimeter observations reveal several clear structures extending to ∼240 au from the stars. Based on these observations at different wavelengths, we report the following discoveries. One arm-like structure detected in the near-infrared band initially extends from the south of the binary with a subsequent turn to the northeast, corresponding to two bar-like structures detected in ALMA observations with an local standard of rest kinematic (LSRK) velocity of 1.19-5.64 km s . Another feature detected in the near-infrared band extends initially from the north of the binary, relating to an arm-like structure detected in ALMA observations with an LSRK velocity of 8.17-16.43 km s . From their shapes and velocities, we suggest that these structures can mostly be explained by two streamers that connect the outer circumbinary disk and the central binary components. These discoveries will be helpful for understanding the evolution of streamers and circumstellar disks in young binary systems. -1 -1

SMI (SPICA Mid-infrared Instrument) is one of the three focal-plane science instruments for SPICA. SMI is the Japanese-led instrument proposed and managed by a university consortium. SMI covers the wavelength range from 10 to 36 μm with four separate channels: the low-resolution (R = 60 - 160) spectroscopy function for 17 - 36 μm, the broad-band (R = 5) imaging function at 34 μm, the mid-resolution (R = 1400 - 2600) spectroscopy function for 18 - 36 μm, and the high-resolution (R = 29000) spectroscopy function for 10 - 18 μm. In this presentation, we will show the latest design and specifications of SMI as a result of feasibility studies.

We present an overview of the cryogenic system of the next-generation infrared observatory mission SPICA. One of the most critical requirements for the SPICA mission is to cool the whole science equipment, including the 2.5 m telescope, to below 8 K to reduce the thermal background and enable unprecedented sensitivity in the mid- and far-infrared region. Another requirement is to cool focal plane instruments to achieve superior sensitivity. We adopt the combination of effective radiative cooling and mechanical cryocoolers to accomplish the thermal requirements for SPICA. The radiative cooling system, which consists of a series of radiative shields, is designed to accommodate the telescope in the vertical configuration. We present thermal model analysis results that comply with the requirements to cool the telescope and focal plane instruments.

The Space Infrared Telescope for Cosmology and Astrophysics (SPICA) mission is to be launched into orbit around the second Lagrangian point (L2) in the Sun-Earth system. Taking advantage of the thermal environment in L2, a 2.5m-class large IR telescope is cooled below 8K in combination with effective radiant cooling and a mechanical cooling system. SPICA adopts a cryogen-free system to prevent the mission operation lifetime being limited by the amount of cryogen as a refrigerant. Currently, the mechanical cooler system with the feasible solution giving a proper margin is proposed. As a baseline design, 4K / 1K-class Joule-Thomson coolers are used to cool the telescope and thermal interface for Focal Plane Instruments (FPIs). Additionally, two sets of double stage stirling coolers (2STs) are used to cool the telescope shield. In this design, nominal operation of FPIs can be kept when one mechanical cooler is in failure. In this paper, current baseline configuration of the mechanical cooler system and current status of mechanical coolers developments which need to satisfy the specific requirements of SPICA cryogenic system are presented.

The ESA/JAXA SPICA mission is a candidate for the ESA Cosmic Vision Medium Class M5 opportunity. Since 2019 an Airbus Defence and Space team has been performing a trade-off study (on behalf of ESA) to establish a baseline telescope optical configuration and design, which can meet the mission scientific performance requirements. This paper describes the telescope baseline design selected, with first estimates of the expected optical performance. The optical design wavelength is 20 microns for an operating temperature of 8 K covering a total bandwidth of 12 to 420 microns over a 30 arc minutes field of view, with a total required collecting area of at least 4.0 m2;. The fundamental mission science driver is to achieve a sky background (astrophysical sources) limited performance. The telescope is designed to illuminate three instruments namely; SMI (JAXA - Japan), SAFARI (SRON - Netherlands) and B-BOP (CEA - France).

We measured the transmittance of low-resistivity (∼10 2 ωcm) and high-resistivity (> 10 10 ωcm) CdZnTe, which are candidates for Immersion grating (IG) in 10-18μm wavelength, at cryogenic temperature. IG is a compact diffraction grating and we are developing a cryogenically operated 10-18μm IG for SMI/HR (SPICA Mid-Infrared Instrument / High-Resolution spectrometer) of SPICA (SPace Infrared telescope for Cosmology and Astrophysics) We performed two experiments: Transmittance measurement with a convergent light Fourier transform spectrometer, and with a collimated lamp beam system. Our result shows that the low-resistivity CdZnTe has large absorption (> 0.5 cm {-1}) and the high-resistivity CdZnTe has low absorption (< 0.1 cm {-1}) at 8.5K at 10-18 μm. The high-resistivity CdZnTe is promising as an IG material although higher precision measurement is needed to determine whether it meets the absorption coefficient requirement (< 0.01 cm {-1}) at cryogenic temperature.

The SR 24 multistar system hosts both circumprimary and circumsecondary disks, which are strongly misaligned with each other. The circumsecondary disk is circumbinary in nature. Interestingly, both disks are interacting, and they possibly rotate in opposite directions. To investigate the nature of this unique twin disk system, we present 0.″1 resolution near-infrared polarized intensity images of the circumstellar structures around SR 24, obtained with HiCIAO mounted on the Subaru 8.2 m telescope. Both the circumprimary disk and the circumsecondary disk are resolved and have elongated features. While the position angle of the major axis and radius of the near-IR (NIR) polarization disk around SR 24S are 55° and 137 au, respectively, those around SR 24N are 110° and 34 au, respectively. With regard to overall morphology, the circumprimary disk around SR 24S shows strong asymmetry, whereas the circumsecondary disk around SR 24N shows relatively strong symmetry. Our NIR observations confirm the previous claim that the circumprimary and circumsecondary disks are misaligned from each other. Both the circumprimary and circumsecondary disks show similar structures in CO observations in terms of its size and elongation direction. This consistency is because both NIR and CO are tracing surface layers of the flared disks. As the radius of the polarization disk around SR 24N is roughly consistent with the size of the outer Roche lobe, it is natural to interpret the polarization disk around SR 24N as a circumbinary disk surrounding the SR 24Nb-Nc system. 12 12

© 2020 Knowledge Systems Institute Graduate School. All rights reserved. Necessary and sufficient combinatorial testing is important especially for continuous development to provide stateful service APIs that are invoked by an unspecified number of users. Listing API call sequences for this type of test cases is an important factor in achieving both high test coverage and short time required for test execution. This paper proposes a method to list fewer call sequences without reducing API coverage, and a method to measure the degree of adequacy of an API sequence for testing. Evaluations of more than 400 services show that the listing method reduces the number of sequences for half of the services, and that the measurement method can determine whether the reduction is possible or not for each service with high probability.