We describe a cell culture experiment utilizing Mars soil simulant and yeast as a study for extraterrestrial-microorganism detection in future. The following conditions were combined to create different sample configurations: solid medium (agar plate) or liquid medium, with the Mars soil simulant (100 mg) or without, and various yeast cell densities (30 μL of a suspension of yeast prepared to achieve dilution rates of 10−2, 10−3, 10−4, and 10−5 from the original suspension). For redundancy, two samples were created for each setting. On each agar plate, colonies of yeast cells were visible. In contrast, only samples created with a dilution rate of 10−2 and 10−3 were proven to show the presence of yeast proliferating in liquid media. The agar plates were observed via imaging using a digital camera. Colony counting was conducted using functions of the ImageJ software; the yeast density in the original suspension was estimated to be 2.5 × 107 colony forming units (CFU)/mL. Based on the results of cell culture on the agar plates, the detection limit that was experimentally demonstrated in this work amounted to 7.5 CFU/100 mg of soil, which corresponded to 75 CFU/g of soil. Thus, we confirmed that the Mars soil simulant reduced the number of colonies to one-third of that detected without the Mars soil simulant. In the discussion, we pointed out that the method that used the solid media has potential to provide high sensitivity using a simple, compact, and lightweight hardware. Microscope with no optics is also discussed. The lower limit of detection obtained in this study was compared with those obtained using other methods. We compared and discussed extraterrestrial life search based on (1) in situ experiments by unmanned missions, (2) analysis of samples returned to Earth, and (3) dedicated in situ analyses by manned bases located on extraterrestrial sites in the future. The perspectives discussed herein are applicable not only to the samples from Mars but also to the samples from other solar system bodies. Identifying cell culture conditions for these applications is a critical difficulty. Notably, it is a possible scenario that cell culture (although challenging) will become necessary to obtain clear evidence of extraterrestrial life. We also note that in cases where there are multiple species of microorganisms, it can happen that microorganisms that fit the culture conditions used in an experiment are selectively cultured and detected, even if the culture conditions for each species are not fully discovered. It is worthwhile to conduct exploration in advance designed with the intention of determining culture conditions with the plan to culture microorganisms in the future.
We are developing optical parts made of infrared-transmitting glass, which can be used in various fields of science and in other applications. Herein, spectral dispersers were fabricated from FI-02, which is developed by Nippon Electric Glass Co., Ltd. The radiation test showed that FI-02 is resistant to radiation. Further, a reflection coating to produce an immersion grating made of FI-02 was tested. We designed, manufactured, and evaluated a prototype grating made of FI- 02. The dimensions of the prototype grating were 30 mm × 20 mm, and the pitch of the steps of the grating was 0.217 mm. We observed the microscopic structure of the steps of the prototype grating. The surface roughness values of the wide and narrow surfaces of the steps were 0.084 μm rms (0.070 μm Ra) and 0.082 μm rms (0.064 μm Ra), respectively. The radius of curvature of the edge of the step was also quantified.
The mid-infrared spectrometer and camera transit spectrometer (MISC-T) is one of the three baseline instruments for Origins Space Telescope (Origins) and provides the capability to assess the habitability of nearby exoplanets and search for signs of life. MISC-T employs a densified pupil optical design, and HgCdTe and Si:As detector arrays. This optical design allows the instrument to be relatively insensitive to minor line-of-sight pointing drifts and telescope aberrations, and the detectors do not require a sub-Kelvin refrigerator. MISC-T has three science spectral channels that share the same field-of-view by means of beam splitters, and all channels are operated simultaneously to cover the full spectral range from 2.8 to 20 μm at once with exquisite stability and precision (<5 ppm between 2.8 to 11 μm, <20 ppm between 11 and 20 μm). A Lyot-coronagraph-based tip–tilt sensor located in the instrument fore-optics uses the light reflected by a field stop, which corresponds to 0.3% of the light from the target, to send fine pointing information to the field steering mirror in the Origins telescope. An additional MISC Wide Field Imager (WFI) is studied as an upscope option for the Origins. MISC-WFI offers a wide field imaging (3 ′ × 3 ′ ) and low-resolution spectroscopic capability with filters and grating-prisms (grisms) covering 5 to 28 μm. The imaging capability of the MISC-WFI will be used for general science objectives. The low-resolution spectroscopic capability in MISC-WFI with a resolving power R ( = λ / Δλ) of a few hundreds will be used to measure the mid-infrared dust features and ionic lines at z up to ∼1 in the Origins mission’s Rise of Metals and Black Hole Feedback programs. The MISC-WFI also serves as a focal plane pointing and guiding instrument for the observatory, including when the MISC-T channel is performing its exoplanet spectroscopy observations.
We present optical design of wideband spectrometer for space-borne telescopes for science observation. Multi-channel configuration is adopted to cover wide wavelength region from visible to mid-infrared. Basic design of each channels are consisting of mirror optics and reflective spectral disperser. Low, medium, and high dispersion spectrometers are studied. Influence of defocusing is analyzed. Each channels are combined based on use of dichroic mirrors.
K. Enya, M. Kobayashi, K. Ishibashi, S. Kobayashi, N. Namiki, H. Araki, S. Tazawa, H. Noda, S. Oshigami, S. Kashima, M. Utsunomiya, J. Kimura, K. Touhara, T. Yamawaki, S. Iwamura, N. Fujishiro, Y. Matsumoto, T. Iida, H. Nakagawa, H. Imai, O. Kirino, C. Hatakeyama, T. Yokozawa, Y. Sato, K. Kojima, N. Matsui, K. Tanimoto, M. Fujii, C. Althaus, S. Del Togno, J. Jänchen, B. Borgs, T. Behnke, H. G. Lötzke, R. Kallenbach, K. Lingenauber, H. Hussmann
The Jupiter Icy Moons Explorer (JUICE) mission of the European Space Agency to be launched in 2022 will provide an opportunity for a dedicated exploration of the Jovian system including its icy moons. The Ganymede Laser Altimeter (GALA) has been selected as one of the ten payloads of JUICE. GALA will enable unique studies of the topography and shape, tidal and rotational state, and geology of primarily Ganymede but also Europa and Callisto. The GALA project is an ongoing international collaboration led by Germany, together with Switzerland, Spain, and Japan. This paper presents the optical and mechanical design of the focal plane receiver, the Japanese part of GALA.
The Mid-infrared Imager, Spectrometer, Coronagraph (MISC) is one of the instruments studied both for the Origins Space Telescope (OST) Mission Concept 1 and 2. The MISC for OST Mission Concept 1 consists of the MISC imager and spectrometer module (MISC I and S), the MISC coronagraph module (MISC COR) and the MISC transit spectrometer module (MISC TRA). The MISC I and S offers (1) a wide field (3 arcminx3 arcmin) imaging and low-resolution spectroscopic capability with filters and grisms for 6-38 μm, (2) a medium-resolution (R~1,000) Integral Field Unit (IFU) spectroscopic capability for 5- 38 μm and (3) a high-resolution (R~25,000) slit spectroscopic capability for 12-18 μm and 25-36 μm. The MISC COR module employs PIAACMC coronagraphy method and covers 6-38 μm achieving 10-7 contrast at 0.5 arcsec from the central star. The MISC TRA module employs a densified pupil spectroscopic design to achieve 3-5 ppm of spectro-photometric stability and covers 5-26 μm with R=100-300. The MISC for OST Mission Concept 2 consists of the MISC wide field imager module (MISC WFI) and the MISC transit Spectrometer module (MISC TRA). The MISC WFI offers a wide field (3 arcmin ×3 arcmin) imaging and low-resolution spectroscopic capabilities with filters and grisms for 6-28μm. The MISC TRA module in the OST Mission Concept 2 also employs the densified pupil spectroscopic design to achieve <5 ppm of spectro-photometric stability and covers 4-22 μm with R=100-300. The highest ever spectrophotometric stability achieved by MISC TRA enables to detect bio-signatures (e.g., ozone, water, and methane) in habitable worlds in both primary and secondary transits of exoplanets and makes the OST a powerful tool to bring an revolutionary progress in exoplanet sciences. Combined with the spectroscopic capability in the FIR provided by other OST instruments, the MISC widens the wavelength coverage of OST down to 5μm, which makes the OST a powerful tool to diagnose the physical and chemical condition of the ISM using dust features, molecules lines and atomic and ionic lines. The MISC also provides the OST with a focal plane guiding function for the other OST science instruments as well as its own use.
The Mid-infrared Imager, Spectrometer Coronagraph (MISC) instrument studied for the Origins Space Telescope (OST) Mission Concept 1 is designed to observe at mid-infrared (MIR) wavelengths ranging from 5 to 38 microns for OST. In the OST Mission Concept 1 study, MISC consists of three separate optical modules providing imaging, spectroscopy, and coronagraph capabilities. The MISC Coronagraph module (MISC COR) employs Phase-Induced Amplitude Apodization (PIAA) coronagraph (Guyon et al. 2014) in which pupil apodization is modified by reflection on mirrors and central starlight is blocked by focal plane mask and Lyot mask. The performance target of MISC COR is to achieve 10-7 contrast at 0.5” from the central star with covering wavelength of 6-38 microns using 2 optical channels. MISC COR will be a powerful tool to bring a revolutionary progress in exoplanet sciences. In this paper, we present detailed design of its optics and optomechanics, and discuss expected performances for a variety of combination of focal plane mask and Lyot mask.
We present concept and laboratory demonstration of high-contrast apodization baffle for instruments to be carried on exploration missions of the solar system. The primary science objective of the high-contrast baffle is to reveal escape of atmosphere on Mars, while other faint objects around blight sources are potential targets. We diverted heritages studied for exoplanet science and instrumentation to this work. The apodization in this work is realized by edge with microscopic Gaussian shaped structure. A simulation to confirm the concept and design of the high-contrast apodization baffle was carried out. Then, a baffle which was consisting of transparent flat substrate and thin film of aluminum on it was manufactured. The experiment was executed with He-Ne laser with wavelength of 633 nm. As the result, it was demonstrated that the apodization by the Gaussian edge is significantly working to improve the contrast. Achieved contrast is better than 10-6.5 and 10-8 in θ > 0.5 degree and θ > 1 degree, respectively. These results satisfy the requirement for remote sensing of the atmospheric less on Mars.
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 are developing a photonic crystal superlens based on negative refraction effect for mid-infrared astronomical telescopes to improve their angular resolution. The superlens will convert incident beams of large F-number to output beams of small F-number without changing image height. Firstly, we designed the superlens by theoretical calculations. We optimized two-dimensional dielectric structures of the superlens by calculating its band structures and iso-frequency contours using Plane-wave expansion (PWE) method. We also studied interface structures of input/output ports of the superlens in order to maximize its transmittance by numerical calculations using Fourier modal method (FMM). Then, wave-propagation simulations through the superlens by Finite-difference time-domain (FDTD) method showed that Full Width Half Maximum (FWHM) of point spread function will be reduced by approximately 15%. Secondly, we are trying to manufacture the superlens using a three-dimensional laser lithography system based on two-photon polymerization process. We also have measured complex refractive indices of SU-8 photoresist around wavelength of 10micron by spectroscopic ellipsometry. The fabrication and optical benchmark of the superlens are currently underway. In this paper, we present experimental results as well as the design process of the superlens.
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.
We present the development of wideband spectral dispersers of which the primary scientific objective is the characterization of the atmospheres of exoplanets, including the challenge of detecting biomarkers. A disperser comprising a prism with a grating pattern on its surface provides simultaneous wideband coverage with low spectral resolution (R ≥ 300). The optics is simple, compact, and contains no moving parts. A comparative study of 21 materials for the disperser was carried out for use in the optical, near-infrared, and mid-infrared wavelength regions. KRS-5, CdZnTe, ZnS LiF, Sapphire, and S-TIH11 were selected, and designs of the optics for single-channel wideband spectrometers using the selected six materials were considered. Then, trial designs of the multi-channel spectrometers were carried out taking the properties of the detectors into consideration. The 3-channel design covers the wavelength region of ∼0.2−23 μm using a CCD detector, an InSb detector, and a Si:As detector. The 2-channel design covers ∼0.4−23 μm using a HgCdTe detector and a Si:As detector. A fabricated ZnS disperser is shown together with a CsI subprism which compensates for the optical axis. The application of defocusing, high dispersion spectroscopy, extension to the UV wavelength region, and the combination of the disperser with future space telescopes are discussed.
CRAO is a demonstrator of a compact and low-cost adaptive-optics (AO) with a double-pass lens configuration. Owing
to its compact optical layout compared to conventional reflective AOs, the instrument size can be reduced to only 0.03
square meters. We plan to apply this miniaturization technique into future AOs on a variety of telescopes ranging from 1m-
to 30m-class. CRAO is installed at a Nasmyth focus of the 1.3m Araki telescope at Koyama Astronomical Observatory
in Kyoto Sangyo University. CRAO adopts a closed-loop single-conjugate system with wavelength coverage of 400 -
700 nm and the field of view of 30 arcsec. For low cost, we also employ commercial products on its wavefront sensor
(WFS), deformable mirror (DM), and tip-tilt (TT) stage. CRAO is designed to improve the atmospheric seeing from 2.5
to 0.6arcsec under a typical condition at Koyama Astronomical Observatory with 12x12 subapertures in the WFS, 48
electrodes in the membrane DM and the control bandwidth of 200Hz. In order to examine key issues inherent in refractive
optical system such as chromatic aberration, temperature aberration and ghost images, room and on-sky experiments are
currently underway. CRAO has seen first light in May 2014, and we have confirmed that effects of chromatic aberration and
ghost images induced by its refractive optics are negligible for at least TT correction. In this paper, we present experimental
results as well as the design of optics, opto-mechanics and control system.
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.
We have carried out the trial production of small format (n=5) image slicer aiming to obtain the technical verification of the Integral Field Unit (IFU) that can be equipped to the next generation infrared instruments such as TMT/MICHI and SPICA/SMI. Our goal is to achieve stable pseudo slit image with high efficiency. Here we report the results of the assembly of the image slicer unit and the non-cryogenic evaluation system of the pseudo slit image quality in the infrared.
An image slicer is highly in demand for an integral field unit (IFU) spectrograph of the next generation infrared
telescopes. This paper reports the results of the trial production of three key optical elements for a small format (number
of slice; n=5) image slicer, i.e. monolithic slice mirrors, monolithic pupil mirrors and monolithic pseudo slit mirrors. We
have demonstrated that sufficiently high processing accuracy and mirror surface accuracy for infrared observations are
achieved for each optical element based on our super precision cutting techniques.
Mid-infrared Medium Resolution Spectrometer (MRS) is one of the key spectroscopic modules of Mid-
Infrared Camera and Spectrometers (MCS) that will be onboard SPICA. MRS is an Echelle Grating
spectrometer designed to observe a number of fine structure lines of ions and atoms, molecular lines, and
band features stemming from solid particles and dust grains of the interstellar and circumstellar
medium in the mid-infrared wavelength range. MRS consists of two channels; the shorter wavelength
channel (MRS-S) covers the spectral range from 12.2 to 23.0 micron with a spectral resolution power of
R~1900-3000 and the longer wavelength channel (MRS-L) covers from 23.0 to 37.5 micron with
R~1100-1500 on the basis of the latest results of the optical design. The distinctive functions of the
MRS are (1) a dichroic beam splitter equipped in the fore-optics, by which the same field of view is
shared between the two channels, and (2) the small format image slicer as the integral field unit
installed in each channel. These functions enable us to collect continuous 12-38 micron spectra of both
the point-like and diffuse sources reliably with a single exposure pointed observation. In this paper, the
specifications and the expected performance of the MRS are summarized on the basis of the latest
results of the optical design. The latest progress in the development of the key technological elements,
such as the Dichroic Beam Splitter and the Small Format Monolithic Slice Mirrors, are also reported.
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.
We report the system/optics design and performance of the dome flat-field system for the Araki Telescope, a 1.3- m optical/near-infrared telescope at Koyama Astronomical Observatory in Japan. A variety of instruments are attached to the telescope. The optical imager, which is intended to search for exoplanets, requires an illumination flatness within 1% on the focal plane over the 17-arcmin FOV. Illumination flatness at both the pupil plane and the focal plane of the telescope is essential for calibration of the transmittance of the optical system. We devised an optical design for the flat-field system that satisfies illumination flatness at both the focal and pupil planes using the non-sequential ray tracing software LightTools. We considered far-field illumination pattern of the lamps, scattering surface reflectance distribution of the screen, telescope structure, primary/secondary mirrors, and mirror baffles. We achieved a flat illumination distribution of 0.9% at the focal plane. The systems performance was tested by comparison with a cloud-flat frame, which was derived by imaging cloud cover illuminated by city lights. The calibration data for the dome flat-field system agree well with the cloud-flat frame within 1% for the g′ and i′ bands of the imager, but the r0 band data does not meet the requirement (less than or equal to 2). Moreover, various instruments require a focal plane illuminance ranging over three orders of magnitude. We used six high-power (60W) halogen lamps; the output power is remotely controlled by a thyristor-driven dimmer and a bypass circuit to an autotransformer.
SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is an astronomical mission optimized for
mid- and far-infrared astronomy, envisioned for launch in 2018. Mid-infrared instruments for SPICA are
required to have three basic capabilities; a wide-field imaging, spectroscopic capability, and coronagraphic
capability as an option. First two capabilities are implemented by three instruments; MIRACLE(Mid-infRAred
Camera w/o Lens), MIRMES(Mid-IR Medium-resolution Echelle Spectrometer), and MIRHES(Mid-IR High-resolution
Echelle Spectrometer). Here, we present an optical architecture of the union of MIRACLE, MIRMES,
and MIRHES. MIRACLE has two channels (-S for short wavelength and -L for long wavelength) to cover the
wavelength range 5 to 40 micron. MIRACLE-L and MIRMES are packaged into one unit with common optical
bench and MIRACLE-S and MIRHES are packaged into another unit. Two units are independent with each
other and occupy different field of view of the SPICA telescope. Each unit has common fore-optics shared by
MIRACLE and MIR(M/H)ES. This fore-optics is designed using reflective mirror optics only, and has wide
filed of view(FOV). Most of the FOV is used by MIRACLE and small part of the FOV is used by MIRMES
or MIRHES. This structure of the instruments reduces the size and weight of the instruments. This benefit
outweigh the complexity of the instruments.
The Mid-Infrared Medium-Resolution Eschelle Spectrometer (MIRMES) is one of the focal-plane instrument onboard
SPICA mission proposed in the pre-project phase. It is designed for measuring the strengths and the profiles of lines and
bands emitted from various phases of materials including ionized gas, gas-phase molecules, solid-phase molecules and
dust particles in the wavelengths from 10 to 40μm. The MIRMES provides a medium resolution (R=700-1500)
spectroscopic capability in the mid-infrared spectral range (10-36μm) with integrated field units of a field-of-view of
about 12"×6" for shorter wavelength range (10-20μm) and 12"×12".5 for longer wavelength range (20-36μm). The
science targets of the MIRMES and the results of the concept study on its optical design and the expected performance
are described.
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.
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.
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.
The MIR-L is the mid-IR (12-26 μm) instrument for Japanese infrared astronomical satellite, the ASTRO-F. The instrument has 2 observing modes: a wide field imaging mode with a field of view of 10.7 × 10.2 arcmin2 and a low resolution spectroscopic mode with a spectral resolution R = λ/Δλ about 20. The spectroscopic mode provides with not only slit-spectroscopy for extended sources but also slitless-spectroscopy for point sources. We describe here the design, manufacturing, and performance evaluation of the cryogenic optical system of the MIR-L. The concept of the optical system design is to realize wide field observations with a compact size. The instrument employs a refractive optics of 5 lenses (CsI - CsI - KRS-5 - CsI - KRS-5) with a 256×256 pixel Si:As IBC array detector, 3 filters, and 2 grisms. The refractive indices of CsI and KRS-5 at the operating temperature of about 6 K have ambiguities because of the difficulty of the measurements. We therefore designed the MIR-L optics with tolerances for the uncertainties of the indices. Since both CsI and KRS-5 have the fragility and the large thermal expansion, we designed a specialized mounting architecture to prevent from making damages and/or decentrations of the lenses at cryogenic temperatures under the serious vibration during the launch. As a result, the optical system of the MIR-L has passed both vibration and thermal cycle tests without damage and performance degradation, and achieved diffraction limited performance over its full wavelength range at the operating temperature.
The ASTRO-F is an on-going infrared satellite mission covering 2-200 μm infrared wavelengths. Not only the all-sky survey in the mid-IR and far-IR, but also deep pointing observations are planned especially at 2-26 μm. In this paper, we focus on the near-infrared (NIR) channel of the infrared camera (IRC) on board ASTRO-F, and describe its design, and results of the imaging mode performance evaluation as a single component. The NIR consists of 4 lenses (Silicon - Silicon - Germanium - Silicon) with a 412 * 512 In:Sb detector. Three broad-band filters, and two spectroscopic elements are installed covering 2-5 μm wavelengths. Since the ASTRO-F telescope and the focal plane are cooled to 6 K, the evaluation of adjustment of the focus and the end-to-end test of the whole NIR camera assembly have to be done at cryogenic temperature. As a result of measurements, we found that the transverse magnification and distortion are well matched with the specification value (1 versus 1.017 and 1 %), while the chromatic aberration, point spread function, and encircled energy are slightly degraded from the specification (300 μm from 88 μm, > 1pixel from ~ 1pixel, 80 % encircled energy radius > 1pixel from ~ 1pixel). However, with these three measured values, in-flight simulations show the same quality as specification without degradation. In addition to the image quality, we also verified the ghost image generated from the optical element (1 % energy fraction to the original image) and the slightly narrowed field of view (10' * 9.5' from 10' * 10'). For the responsivity, the NIR shows expected response. Totally, the NIR imaging mode shows satisfactory results for the expected in-flight performance.
MIR-L is a 12-26μm channel of Infrared Camera(IRC) onboard ASTRO-F. The camera employs a refractive optics which consists of 5 lenses (CsI - CsI - KRS-5 - CsI - KRS-5) and a large format Si:As IBC array detector (256 x 256 pixels). The design concept is to realize a wide field of view with a compact size. It has 2 observing modes: a wide field imaging with a field of view of 10.7 x 10.2arcmin2 or a pixel resolution of 2.5 x 2.4arcsec2/pixel in 3 bands (12.5-18μm, 14-26μm, 22-26μm), and low resolution spectroscopy with a spectral resolution R = λ/Δλ
≈40 in 2 bands 11-19μm,18-26μm). It also has a small slit to adapt for spectroscopic observations of extended sources. We describe the current design of the optics and the mounting architecture of MIR-L and evaluation of the optical performance at cryogenic temperatures.
The Infrared Camera (IRC) is one of the focal-plane instruments on board the Japanese infrared astronomical space mission ASTRO-F. It will make wide-field deep imaging and low-resolution spectroscopic observations over a wide spectral range in the near- to mid-infrared (2-26um) in the pointed observation mode of the ASTRO-F. The IRC will also be operated in the survey mode and make an all-sky survey at mid-infrared wavelengths. It comprises three channels. The NIR channel (2-5um) employs a 512x412 InSb array, whereas both the MIR-S (5-12um) and the MIR-L (12-26um) channels use 256x256 Si:As impurity band conduction (IBC) arrays. The three channels will be operated simultaneously. All the channels have 10'x10' fields of view with nearly diffraction-limited spatial resolutions. The NIR and MIR-S share the same field of view, while the MIR-L will observe the sky about 25' away from the NIR/MIR-S field of view. The IRC will give us deep insights into the formation and evolution of galaxies, the properties of brown dwarfs, the evolution of planetary disks, the process of star-formation, the properties of the interstellar medium under various physical environments, as well as the nature and evolution of solar system objects. This paper summarizes the latest laboratory measurements as well as the expected performance of the IRC.
An all-sky survey in two mid-infrared bands which cover wavelengths of 5-12um and 12-26μm with a spatial resolution of ~9" is planned to be performed with the Infrared Camera (IRC) on board the ASTRO-F infrared astronomical satellite. The expected detection limits for point sources are few tens mJy. The all-sky survey will provide the data with sensitivities more than one order of magnitude deeper and with spatial resolutions an order of magnitude higher than the Infrared Astronomical Satellite (IRAS) survey.
The IRC is optimally designed for deep imaging in pointing observations. It employs 256x256 Si:As IBC infrared focal plane arrays (FPA) for the two mid-infrared channels. In order to make observations with the IRC during the survey mode of the ASTRO-F, a new operation method for the arrays has been developed - the scan mode operation. In the scan mode, only 256 pixels in a single row aligned in the cross-scan direction on the array are used as the scan detector and sampled every 44ms. Special cares have been made to stabilize the temperature of the array in the scan mode, which enables to achieve a low readout noise compatible with the imaging mode (~30 e-). The flux calibration method in the scan mode observation is also investigated. The performance of scan mode observations has been examined in computer simulations as well as
in laboratory simulations by using the flight model camera and moving artificial point sources. In this paper we present the scan mode operation method of the array, the results of laboratory performance tests, the results of the computer simulation, and the expected performance of the IRC all-sky survey observations.
We report on the extensive tests to characterize the performance of the infrared detector arrays for the Infrared Camera (IRC) on board the next Japanese infrared astronomical satellite, ASTRO-F. The ASTRO-Fwill be launched early 2004 and the IRC is one of the focal plane instruments to make observations in 2-26μm. For the near-infrared observations of 2-5μm, a 512x412 InSb array will be employed, while two 256x256 Si:As arrays will be used for the observations of 5-26μum in the IRC. Both arrays are manufactured by Raytheon.
To maximize the advantage of the cooled telescope and extremely low background radiation conditions in space, the dark current and readout noise must be minimized. The heat dissipation of the arrays also has to be minimized. To meet these requirements and achieve the best performance of the arrays, we optimized the array driving clocks, the bias voltage, and the supply currents, and evaluated the temperature dependence of the performance. In particular, we found that the voltage between the gate and source of the FET of the multiplexer SBRC-189 had a strong dependence on temperature. This effect becomes a dominant source for the noise unless the temperature
is kept within 20mK. We have achieved the readout noises of about 30e- and 40e- with the correlated double sampling for the flight model readout circuits of the InSb and Si:As arrays, respectively. These noises ensure that the background-limited performance can be achieved for the observations of IRC in the 4-26μm range in the current observing scheme.
In addition, we are now planning to make scan mode observations by IRC. We have developed a new operation way of the arrays to achieve the stable response and low readout noise in the scanning operation for the first time.
The IRC is now installed in the flight model cryostat and the first
end-to-end test has just been completed. We report on the expected performance of the IRC together with the array test results.
The infrared camera(IRC) onboard ASTRO-F is designed for wide-field imaging and spectroscopic observations at near- and mid-infrared wavelengths. The IRC consists of three channels; NIR, MIR-S and MIR-L, each of which covers wavelengths of 2-5, 5-12 and 12-26 micron, respectively. All channels adopt compact refractive optical designs. Large format array detectors (InSb 512x412 and Si:As IBC 256x256) are employed. Each channel has 10x10 arcmin wide FOV with diffraction-limited angular resolution of the 67cm telescope of ASTRO-F at wavelengths over 5 micron. A 6-position filter wheel is placed at the
aperture stop in each channel, and has three band-pass filters, two grisms/prisms and a mask for dark current measurements. The 5 sigma sensitivity of one pointed observation is estimated to be 2, 11 and 62 micro-Jy at 4, 9, 20 micron bands, respectively. Because ASTRO-F is a low-earth orbiting satellite, the observing duration of each pointing is limited to 500 seconds. In addition to pointed observations, we plan to perform mid-infrared scanning observation.
Fabrications of the flight-model of NIR, MIR-S, and the warm electronics have been mostly completed, while that of MIR-L is underway. The performance evaluation of the IRC in the first end-to-end test (including the satellite system) is presented.
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