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.
GREX-PLUS (Galaxy Reionization EXplorer and PLanetary Universe Spectrometer) is a new mission concept for ISAS/JAXA’s strategic L-class mission program in the 2030s. With a 1.2 m aperture, a 50 K cryogenic space telescope will have a < 1, 400 arcmin2 wide-field camera with 6 bands in the 2–10 μm wavelength range and a high-dispersion spectrometer with a wavelength resolution of < 30, 000 in the 10–18 μm band. The cryogenic infrared mission concept of GREX-PLUS is based on SPICA, exploiting the technical resources so far studied and developed, such as an active cooling system. The high-dispersion spectrometer of GREX-PLUS is based on the high-dispersion channel of the SPICA Mid-Infrared Instrument (SMI). The wide-field camera of GREX-PLUS is also based on previous concept studies for the ISAS/JAXA’s WISH mission concept. GREX-PLUS is a concept proposal for a Japan-led mission but international collaborations are also welcome.
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.
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 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.
SMI (SPICA Mid-infrared Instrument) is one of the two focal-plane science instruments for SPICA. SMI is the Japanese led instrument proposed and managed by a nation-wide university consortium in Japan and planned to be developed in collaboration with Taiwan and the US. SMI covers the wavelength range from 12 to 36 μm with 4 separate channels: the low-resolution (R = 50-120) spectroscopy function for 17-36 μm, the broad-band (R = 5) imaging function at 34 μm, the mid-resolution (R = 1300-2300) spectroscopy function for 18-36 μm, and the high-resolution (R = 28000) spectroscopy function for 12-18 μm. In this paper, we show the results of our conceptual design and feasibility studies of SMI.
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.
We present the latest results of the sensitivity estimate for spectrometers of the SPICA Mid-Infrared
Instrument (SMI). SMI has three spectroscopic channels; low resolution spectrometer (LRS), medium
resolution spectrometer (MRS) and high resolution spectrometer (HRS). Taking account of the results of
optical design of each spectrometer and the latest information of the expected performance of detector
arrays, the continuum sensitivity for a point source, the continuum sensitivity for an extended source,
the line sensitivity for a point source, the line sensitivity for an extended source, and the saturation limit
are calculated for LRS, MRS and HRS and are provided in this paper.
SMI (SPICA Mid-infrared Instrument) is one of the two focal-plane scientific instruments planned for new SPICA, and
the Japanese instrument proposed and managed by a university consortium in Japan. SMI covers the wavelength range of
12 to 36 μm, using the following three spectroscopic channels with unprecedentedly high sensitivities: low-resolution
spectroscopy (LRS; R = 50 - 120, 17 - 36 μm), mid-resolution spectroscopy (MRS; R = 1300 - 2300, 18 - 36 μm), and
high-resolution spectroscopy (HRS; R = 28000, 12 - 18 μm). The key functions of these channels are high-speed dustband
mapping with LRS, high-sensitivity multi-purpose spectral mapping with MRS, and high-resolution molecular-gas
spectroscopy with HRS. This paper describes the technical concept and scientific capabilities of SMI.
We present the design, fabrication and test results for a dichroic mirror, which was primarily developed for the SPICA Coronagraph Instrument (SCI), but is potentially useful for various types of astronomical instrument. The dichroic mirror is designed to reflect near- and mid-infrared but to transmit visible light. Two designs, one with 3 layers and one with 5 layers on BK7 glass substrates, are presented. The 3-layer design, consisting of Ag and ZnS, is simpler, and the 5-layer design, consisting of Ag and TiO2 is expected to have better performance. Tape tests, evaluation of the surface figure, and measurements of the reflectivity and transmittance were carried out at ambient temperature in air. The reflectivity obtained from measurements made on mirrors with 5 layers were < 80 % for wavelengths, λ, from 1.2 to 22 μm and < 90 % for λ from 1.8 to 20 μm. The transmittance obtained from measurements made on mirrors with 5 layers were < 70 % for λ between 0.4 and 0.8 μm. Optical ghosting is estimated to be smaller than 10-4 at λ < 1.5 μm. A protective coating for preventing corrosion was applied and its influence on the reflectivity and transmittance evaluated. A study examining the trade-offs imposed by various configurations for obtaining a telescope pointing correction signal was also undertaken.
In this report we describe our development of a prototype inverse-polished mirror for the passive correction of the static
and predictable wavefront errors (WFE) of space-based telescopes, in particular, especially for infrared coronagraphs.
An artificial WFE pattern with a root mean square (rms) value of 350 nm was numerically generated to facilitate the
design of the prototype mirror. The surface of the mirror is approximately flat, is 50.0 mm in diameter and 15.0 mm
thick at the edge. The designed WFE pattern was constructed on the mirror surface by micro-polishing. Both the figure
and roughness of the mirror surface were evaluated. The rms value of the measured surface figure was reduced to 135
nm after subtraction of the designed surface figure. The benefit of subtraction to mid-infrared coronagraph performance
was simulated, which showed the contrast was improved by a factor of ~100 close to the core (closer than 10 λ/D where
λ and D are the wavelength and telescope aperture diameter, respectively) of the coronagraphic image of a point source.
An analysis of the power spectrum density shows that the lower frequencies in the WFE are well reproduced on the
mirror, while the higher frequencies remain due to the limitations imposed on the controllable spatial resolution by the
fabrication process. In this study, inverse-polished mirrors combined with deformable mirrors and their application to
ground-based telescopes are also discussed. To fully explore the potential of the inverse-polished mirror, a systematic
allocation of the error budget is essential taking into account not only the fabrication accuracy of the mirror but also an
evaluation of the telescope and other factors with non-predictable uncertainties.
AKARI, the Japanese satellite mission dedicated to infrared astronomy was launched in 2006 February and exhausted its liquid helium in 2007 August. During the cold mission phase, the Infrared Camera (IRC) onboard carried out an all-sky survey at 9 and 18µm with better spatial resolution and higher sensitivity than IRAS. Both bands also have slightly shorter wavelength coverage than IRAS 12 and 25μm bands and thus provide different information on the infrared sky. All-sky image data of the IRC are now in the final processing and will be released to the public within a year. After the exhaustion of the cryogen, the telescope and focal plane instruments of AKARI had still been kept at sufficiently low temperatures owing to the onboard cryocooler. Near-infrared (NIR) imaging and spectroscopic observations with the IRC had continued until 2011 May, when the spacecraft had a serious problem in the power supply system that forced us to terminate the observation. The IRC carried out nearly 20000 pointing observations in total despite of its near-earth orbit. About a half of them were performed after the exhaustion of the cryogen in the spectroscopic modes, which provided high-sensitivity NIR spectra from 2 to 5µm without disturbance of the terrestrial atmosphere. During the warm mission phase, the temperature of the instrument gradually increased and changed the array operation conditions. We present a summary of AKARI/IRC observations, including the all-sky mid-infrared diffuse data as well as the data taken in the warm mission phase.
We present the current status of the development of the SPICA Coronagraph Instrument (SCI). SPICA is a next-generation
3-meter class infrared telescope, which will be launched in 2022. SCI is high-contrast imaging, spectroscopic
instrument mainly for direct detection and spectroscopy of extra-solar planets in the near-to-mid infrared wavelengths to
characterize their atmospheres, physical parameters and evolutionary scenarios. SCI is now under the international
review process. In this paper, we present a science case of SCI. The main targets of SCI, not only for direct imaging but
also for spectroscopy, are young to matured giant planets. We will also show that some of known exoplanets by ground-based
direct detection are good targets for SCI, and a number of direct detection planets that are suitable for SCI will be
significantly increased in the next decade. Second, a general design of SCI and a key technology including a new high-throughput
binary mask coronagraph, will be presented. Furthermore, we will show that SCI is potentially capable of
achieving 10-6 contrast by a PSF subtraction method, even with a telescope pointing error. This contrast enhancement
will be important to characterize low-mass and cool planets.
WISH, Wide-field Imaging Surveyor for High-redshiftt, is a space mission concept to conduct very deep and widefield
surveys at near infrared wavelength at 1-5μm to study the properties of galaxies at very high redshift beyond the
epoch of cosmic reionization. The concept has been developed and studied since 2008 to be proposed for future
JAXA/ISAS mission. WISH has a 1.5m-diameter primary mirror and a wide-field imager covering 850 arcmin2. The
pixel scale is 0.155 arcsec for 18μm pitch, which properly samples the diffraction-limited image at 1.5μm. The main
program is Ultra Deep Survey (UDS) covering 100 deg2 down to 28AB mag at least in five broad bands. We expect to
detect <104 galaxies at z=8-9, 103-104 galaxies at z=11-12, and 50-100 galaxies at z<14, many of which can be feasible
targets for deep spectroscopy with Extremely Large Telescopes. With recurrent deep observations, detection and light
curve monitoring for type-Ia SNe in rest-frame infrared wavelength is also conducted, which is another main science
goal of the mission. During the in-orbit 5 years observations, we expect to detect and monitor <2000 type-Ia SNe up to
z~2. WISH also conducts Ultra Wide Survey, covering 1000deg2 down to 24-25AB mag as well as Extreme Survey,
covering a limited number of fields of view down to 29-30AB mag. We here report the progress of the WISH project
including the basic telescope and satellite design as well as the results of the test for a proto-model of the flip-type filter
exchanger which works robustly near 100K.
SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is an astronomical mission optimized for
mid- and far-infrared astronomy, envisioned for launch in early 2020s. The core wavelength coverage of this
mission is 5 to 200 micron. Mid-infrared Camera and Spectrometer (MCS) will provide imaging and spectroscopic
observing capabilities in the mid-infrared region with 4 modules. WFC (Wide Field Camera) has two 5
arcminutes square field of view and covers the wavelength range from 5 to 38 micron. MRS (Mid Resolution
Spectrometer) has integral field units by image slicer and covers the wavelength range from 12.2 to 37.5 micron
simultaneously using dichroic filter and two sets of spectrometers. HRS (High Resolution Spectrometer) covers
the wavelength range from 12 to 18 micron with resolving power 20000 to 30000, and it has optional short
wavelength channel which covers from 4 to 8 micron with resolving power 30000. LRS (Low Resolution Spectrometer)
adopts prism disperser and covers the wavelength range from 5 to 38 micron with resolving power 50
to 100. Here, we present detailed specifications of MCS, optical design, and estimated performance on orbit.
S. Oyabu, I. Yamamura, C. Alfageme, P. Barthel, A. Cassatella, M. Cohen, N. Cox, E. Figueredo, H. Fujiwara, N. Ikeda, D. Ishihara, W.-S. Jeong, H. Kataza, Do Kester, H. M. Lee, S. Makiuti, T. Mueller, T. Nakagawa, S. Takita, S. H. Oh, S. Oliver, C. Pearson, N. Rahman, M. Rowan-Robinson, A. Salama, R. Savage, S. Serjeant, G. J. White, C. Yamauchi
Bright source catalogues based on the new mid- and far-infrared all-sky survey by the infrared astronomical
satellite AKARI were released into the public domain in March 2010. The mid-infrared catalogue contains
more than 870 thousand sources observed at 9 and 18 μm, and the far-infrared catalogue provides information
of about 427 thousand sources at 65, 90, 140, and 160 μm. The AKARI catalogues will take over the IRAS
catalogues and will become one of the most important catalogues in astronomy. We present the characteristics
of the AKARI infrared source catalogues as well as current activity for the future versions.
KEYWORDS: Galactic astronomy, Space telescopes, Telescopes, Mirrors, Near infrared, Optical filters, Staring arrays, Ultraviolet radiation, James Webb Space Telescope, Sensors
WISH is a new space science mission concept whose primary goal is to study the first galaxies in the early universe.
We will launch a 1.5m telescope equipped with 1000 arcmin2 wide-field NIR camera by late 2010's in order to conduct
unique ultra-deep and wide-area sky surveys at 1-5 micron. The primary science goal of WISH mission is pushing the
high-redshift frontier beyond the epoch of reionization by utilizing its unique imaging capability and the dedicated
survey strategy. We expect to detect ~104 galaxies at z=8-9, ~3-6x103 galaxies at z=11-12, and ~50-100 galaxies at
z=14-17 within about 5 years of the planned mission life time. It is worth mentioning that a large fraction of these
objects may be bright enough for the spectroscopic observations with the extremely large telescopes. By adopting the optimized strategy for the recurrent observations to reach the depth, we also use the surveys to detect transient objects.
Type Ia Supernova cosmology is thus another important primary goal of WISH. A unique optical layout has been
developed to achieve the diffraction-limited imaging at 1-5micron over the required large area. Cooling the mirror and
telescope to ~100K is needed to achieve the zodiacal light limited imaging and WISH will achieve the required
temperature by passive cooling in the stable thermal environment at the orbit near Sun-Earth L2. We are conducting the
conceptual studies and development for the important components of WISH including the exchange mechanism for the
wide-field filters as well as the primary mirror fixation.
KEYWORDS: Near infrared, Spectroscopy, Sensors, Telescopes, Space telescopes, Near infrared spectroscopy, James Webb Space Telescope, Prisms, Astronomy, Cryocoolers
AKARI, the Japanese satellite mission dedicated for infrared astronomy launched in 2006 February, exhausted its 180
litter liquid helium (LHe) in 2007 August. After the LHe exhaustion, the telescope and focal plane of AKARI have still
been kept less than 50K by the onboard cryocooler and near-infrared (NIR) observations with the Infrared Camera (IRC)
are continuing. The data reduction software optimized for the warm mission enables us to carry out efficient and
sensitive observations in the NIR despite the increase of hot pixels. In particular, the NIR spectroscopic capability of
the IRC provides a unique opportunity to obtain spectra in 2.5-5μm with a high sensitivity, which will not be able to be
carried out with any other facilities until JWST. An overview of the AKARI warm mission is given together with the
performance and some observational results taken during the warm mission.
AKARI is the first Japanese astronomical infrared satellite mission orbiting around the Earth in a sun-synchronous
polar orbit at the altitude of 700 km. One of the major observation programs of the AKARI is an all-sky survey in the
mid- to far-infrared spectral regions with 6 photometric bands. The mid-infrared part of the AKARI All-Sky Survey was
carried out with the Infrared Camera (IRC) at the 9 and 18 µm bands with the sensitivity of about 50 and 120 mJy (5σ
per scan), respectively. The spatial resolution is about 9.4" at both bands. AKARI mid-infrared (MIR) all-sky survey
substantially improves the MIR dataset of the IRAS survey of two decades ago and provides a significant database for
studies of various fields of astronomy ranging from star-formation and debris disk systems to cosmology. This paper
describes the current status of the data reduction and the characteristics of the AKARI MIR all-sky survey data.
The Infrared Camera (IRC) is one of two focal-plane instruments on the AKARI satellite. It is designed for
wide-field deep imaging and low-resolution spectroscopy in the near- to mid-infrared (1.8-26.5 micron) in the
pointed observation mode of AKARI. The IRC is also operated in the survey mode to make an All-Sky Survey
at 9 and 18 microns. The IRC is composed of three channels. The NIR channel (1.8-5.5 micron) employs
a 512x412 InSb photodiode array, whereas both the MIR-S (4.6-13.4 micron) and MIR-L (12.6-26.5 micron)
channels use 256x256 Si:As impurity band conduction (IBC) arrays. Each of the three channels has a field-ofview
of approximately 10x10 arcmin., and they are operated simultaneously. The NIR and MIR-S channels share
the same field-of-view by virtue of a beam splitter. The MIR-L observes the sky about 25 arcmin. away from the
NIR/MIR-S field-of-view. The in-flight performance of the IRC has been confirmed to be in agreement with the
pre-flight expectation. More than 4000 pointed observations dedicated for the IRC are successfully completed,
and more than 90% of the sky are covered by the all-sky survey before the exhaustion of the Akari's cryogen. The
focal-plane instruments are currently cooled by the mechanical cooler and only the NIR channel is still working
properly. Brief introduction, in-flight performance and scientific highlights from the IRC cool mission, together
with the result of performance test in the warm mission, are presented.
Infrared Camera (IRC) onboard AKARI satellite has carried out more than 4000 pointed observations during the phases
1 and 2, a significant amount of which were performed in the spectroscopic mode. In this paper, we investigate the
properties of the spectroscopic data taken with MIR-S channel and propose a new data reduction procedure for slit-less
spectroscopy of sources embedded in complicated diffuse background structures. The relative strengths of the 0th to 1st
order light as well as the efficiency profiles of the 2nd order light are examined for various objects taken with MIR-S
dispersers. The boundary shapes of the aperture mask are determined by using the spectroscopic data of uniform zodiacal
emission. Based on these results, if the appropriate template spectra of zodiacal light emission and the diffuse
background emission are prepared and the geometries of the diffuse structures are obtained by the imaging data, we can
reproduce the slit-less spectroscopic patterns made by a uniform zodiacal emission and the diffuse background emission
by a convolution of those template profiles. This technique enables us to obtain the spectra of infrared sources in highly
complicated diffuse background and/or foreground structures, such as in the Galactic plane and in nearby galaxies.
Institute of Astronomy, University of Tokyo is now planning to build a 6.5-m optical-infrared telescope in Atacama, Chile. This project is called "Univ. Tokyo Atacama Observatory (TAO)", and the site evaluation is now under way. As a part of this evaluation process, we started an investigation to compare the astronomical seeing at Atacama with that at Mauna Kea. Here, we report preliminary results of seeing measurements at several sites in Atacama, carried out on October 2003. In order to separate the temporal and site-to-site variation of the seeing, we used two sets of Differential Image Motion Monitors (DIMMs), each of which has two pairs of 7.4 cm sub-apertures with 20.5 cm separation. Three sites were investigated; the point near the TAO weather station (4,950m), the summit of Cello Chico (5,150m) and the point at 5,430m altitude on Cello Toco. Simultaneous measurements were carried out for three half nights out of four half nights measurements. Although the amount of our data is very limited, the results suggest following: 1) Seeing becomes better and more stable as time passing to midnight (eg. From 0."7 to 0."4 at V-band). 2) Higher altitude sites show better seeing than lower altitude sites.
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