To investigate the evolution of our Galaxy, we plan to measure the distances and motions of stars in the Galactic center region. Additionally, our goal is to detect planets within the habitable zone around mid-M-type stars using transit phenomena. To achieve these objectives, we initiated the Japan Astrometry Satellite Mission for Infrared Exploration (JASMINE) project, targeting a 40 microarcsecond annual parallax measurement and aiming photometric accuracy of less than 0.3% for mid-M-type stars. A conceptual study of the observation instrument was conducted. As a result, the telescope is designed with high stability in orbit through carefully chosen materials and a special thermal design. A three-year operation is planned to collect sufficient data for annual parallax measurements. The telescope, with a diameter of 36 cm, covers wavelengths from 1.0 to 1.6 microns using InGaAs detectors. This paper will detail how instrument parameters were selected based on scientific objectives.
Structural, Thermal and Optical Performance (STOP) analysis is performed to investigate the stability of the telescope to be onboard the Japan Astrometry Satellite Mission for INfrared Exploration (JASMINE). In order to perform one of the prime science objectives, high-precision astrometric observations in the wavelength range of 1.0–1.6 µm toward the Galactic center to reveal its central core structure and formation history, the JASMINE telescope is requested to be highly stable with an orbital change in the image distortion pattern being less than a few 10 µas after low-order correction. The JASMINE telescope tried to satisfy this requirement by adopting two design concepts. Firstly, the mirror and their support structures are made of extremely low coefficientof-thermal-expansion materials. Secondly, their temperatures are highly stabilized with an orbital variation of less the 0.1 ◦C by the unique thermal control idea. Through the preliminary STOP analysis, the structural and thermal structural feasibility of the JASMINE telescope is considered. By combining the results of the structural and thermal design, its thermal deformation is estimated. The optical performance of the JASMINE telescope after the thermal deformation is numerically evaluated. It is found that the thermal displacement of the mirrors in the current structural thermal design produces a slightly large focus-length change. As far as the focus adjustment is adequately applied, the orbital variation of the image distortion pattern is suggested to become acceptable after the low-order correction.
JASMINE is a Japanese planned space mission that aims to reveal the formation history of our Galaxy and discover habitable exoEarths. For these objectives, the JASMINE satellite performs high-precision astrometric observations of the Galactic bulge and high-precision transit monitoring of M-dwarfs in the near-infrared (1.0—1.6 µm in wavelength). For feasibility studies, we develop an image simulation software named JASMINE-imagesim, which produces realistic observation images. This software takes into account various factors such as the optical point spread function (PSF), telescope jitter caused by the satellite’s attitude control error (ACE), detector flat patterns, exposure timing differences between detector pixels, and various noise factors. As an example, we report a simulation for the feasibility study of astrometric observations using JASMINE-imagesim. The simulation confirms that the required position measurement accuracy of 4 milliarcseconds for a single exposure of 12.5-mag objects is achievable if the telescope pointing jitter uniformly dilutes the PSF across all stars in the field of view. On the other hand, the simulation also demonstrates that the combination of realistic pointing jitter and exposure timing differences in the detector can significantly degrade accuracy and prevent achieving the requirement. This means that certain countermeasures against this issue must be developed. This result implies that this kind of simulation is important for mission planning and advanced developments to realize more realistic simulations help us to identify critical issues and also devise effective solutions.
There is currently a strong push towards infrared astronomy, like the ground-breaking JWST and the upcoming ROMAN and Gaia NIR missions. The Japanese JASMINE telescope will be the first Near Infrared (NIR) astro-photometric mission to focus on the Galactic central region and, in many senses, it will be pioneering the field of NIR high-precision astrometry for Milky Way (MW) dynamics. In order to test our data processing pipelines, we require a robust and reliable way to generate mock images. In this contribution, we present the JASMINE input catalogue: the most complete census of point-like sources in the NIR towards the Galactic centre. We used this catalogue as a blueprint from which to generate mock sources that resemble real stars as much as possible, while offering also the possibility of generating entirely new sources to compensate for the observational incompleteness. The method, while conceptually simple, requires treating each star of the input catalogue as new evidence that updates our prior knowledge, which in this case is represented by the underlying model of the MW used. The result is a custom probability distribution function for each star from which to draw mock sources. This represents the biggest and most realistic mock catalogue of the MW centre to date. In the future, we will improve it by adding more proper motions and parallaxes to the input catalogue, and by modelling the dependence of the distance on the kinematics.
The Japan Astrometry Satellite Mission for Infrared Exploration (JASMINE) aims at high-precision astrometry in the near-infrared wavelengths (1.0–1.6 μm). This mission focuses on the Galactic center region, obscured by interstellar dust in optical wavelengths. JASMINE’s observation strategy differs from other missions and must be verified via dedicated simulations. To verify the mission concept, we designed a simplified simulation, the JASMINE mini survey, covering three years with 100 orbits. As a simple case, the data obtained in a single satellite orbit are analyzed simultaneously (Plate Analysis). The observation model was made differentiable and implemented as a probabilistic model to make the best use of Stochastic Variational Inference. Model parameters converged to a certain solution, while the observation model contained more than 30,000 parameters. The estimated coordinates well represented the stellar motions expected from the ground truth. A typical positional error was estimated to be about 70 µas, consistent with the measurement error and the number of measurements. The present results validate parts of JASMINE’s mission concepts, leading to significant advancements in understanding the Galactic center.
Time-domain astronomy is important in the field of modern astronomy, and monitoring observations in the mid-infrared region with 1% photometric accuracy to study the variables and transients is becoming essential. The non-uniformity of the sensitivity caused by the optical characteristics of instruments and differences in the response curves of individual detector pixels degrade photometric accuracy. Therefore, to achieve 1% photometric accuracy, a flat-field correction for the non-uniformity with an accuracy of better than 1% is required. We developed a flat calibration unit (FCU) consisting of a silicon lens, a blackbody source, and two flat folding mirrors. We conducted proof-of-concept tests of the FCU by measuring the accuracy and stability of flat frames obtained using the FCU. The accuracies of the flat frames were 0.23% at 7.7 μm, 0.43% at 9.6 μm, 0.34% at 11.5 μm, and 0.84% at 20.9 μm, which are sufficient to achieve 1% photometric accuracy. The flat frames obtained using the FCU were stable over a period of 29 h within the accuracies of 0.13% at 7.7 μm, 0.12% at 9.6 μm, 0.22% at 11.5 μm, and 0.52% at 20.9 μm, indicating that it is sufficient to obtain flat frames once per night.
Cold choppers are fast beam-switching tip-tilt mirrors installed in the cold optics of mid-infrared instruments. They enable chopping observations, required for ground-based mid-infrared observations to subtract the bright background radiation, without moving telescope mirrors. In the era of next-generation extremely large telescopes, the telescope mirrors cannot be moved due to the size. Therefore, cold choppers are a key technology for groundbased mid-infrared instruments for such large telescopes. In this study, we develop a prototype cold chopper for TAO/MIMIZUKU, the mid-infrared instrument for the TAO 6.5-m telescope, and evaluate the performance in a cryogenic environment at 20 K. It is confirmed that the prototype shows almost the same response as at room temperature and achieves 2-axis square-wave motion with an amplitude of 0.84 deg, a settling time of ∼40 ms, and a frequency of ≥2 Hz. The evaluated power dissipation is ∼5mW. Stability is found to be slightly worse than required (6 × 10−4 deg) due to mechanical vibration caused by the cryocooler used in the experiment. We plan to mount this chopper on MIMIZUKU to check the effects of such vibrations in the on-board environment.
MIMIZUKU is a mid-infrared instrument for the TAO 6.5-m telescope under construction in the Atacama Desert, Chile, and will be the world’s first mid-infrared monitoring observation station. We aim to achieve a photometric accuracy of 1%. For this purpose, highly accurate flat fielding with an accuracy of 0.1% is needed. Although flat fielding has been conducted using sky images and dark images conventionally, the correction has uncertainties of several percent. The reason is that the non-linearity of the detector is not considered. To improve this, it is necessary to create flat frames from data in the same count level as during observation. Highly accurate flat frames were derived by taking differential counts against the time variation of the atmospheric radiation. However, this method cannot be used under stable conditions suitable for observations. Therefore, we developed a flat calibration unit which irradiates the detector uniformly and vary the irradiation intensity with time to enable the improved flat fielding under any conditions. We designed the unit that irradiates the detector uniformly by placing a silicon lens and a blackbody source in front of the camera. The blackbody source is put at the pupil position of the optical system. We made some tests to create flat images with the unit. By improving flat fielding, we have successfully corrected for patterns originating from the detector, which appeared in the conventional one. We also clarified that the accuracy of the improved flat fielding was 0.29%, while the accuracy of the conventional one was 1.3%.
Automatic survey observations require a high-resolution cloud monitor providing areas of clear sky to a telescope system. A wide-field thermal camera is a powerful tool for monitoring a cloud distribution regardless of scattered lights from the Moon and nearby cities. We developed a compact mid-infrared all-sky monitor using a waterproof camera module with a Ge lens and an 80 x 80-pixel Si-bolometer array for wavelengths from 8 to 12 microns and a magnifying mirror with a diameter of 100 mm. The magnifier has a rotationally symmetrical shape with a round-shaped cross-section, which produces a radially reversed all-sky image without a shade of the camera body. The camera system is equipped with image processing software for coordinate transformation and linearization. In long-term test observations at Kiso Observatory, we confirmed that the system obtains frames of the sky every 60 sec with sufficient sensitivity to discriminate between clear and obscured areas.
MIMIZUKU is the first-generation mid-infrared instrument for the TAO 6.5-m telescope. It has three internal optical channels to cover a wide wavelength range from 2 to 38 µm. Of the three channels, the NIR channel is responsible for observations in the shortest wavelength range, shorter than 5.3 µm. The performance of the NIR channel is evaluated in the laboratory. Through the tests, we confirm the followings: 1) the detector (HAWAII 1RG with 5.3-µm cutoff) likely achieves ∼80% quantum efficiency; 2) imaging performance is sufficient to achieve seeing-limit spatial resolution; 3) system efficiencies in imaging mode are 2.4–31%; and 4) the system efficiencies in spectroscopic modes is 5–18%. These results suggest that the optical performance of the NIR channel is achieved as expected from characteristics of the optical components. However, calculations of the background levels and on-sky sensitivity based on these results suggest that neutral density (ND) filters are needed to avoid saturation in L ′ - and M′ -band observations and that the ND filters and the entrance window, made of chemical-vapor-deposition (CVD) diamond, significantly degrade the sensitivity in these bands. This means that the use of different window materials and improvements of the detector readout speed are required to achieve both near-infrared and long-wavelength mid-infrared (>30 µm) observations.
The Simultaneous-color Wide-field Infrared Multi-object Spectrograph (SWIMS) is one of the 1st generation facility instruments for the University of Tokyo Atacama Observatory (TAO) 6.5 m telescope currently being constructed at the summit of Cerro Chajnantor (5,640 m altitude) in northern Chile. SWIMS has two optical arms, the blue arm covering 0.9–1.4 µm and the red 1.4–2.5 µm, by inserting a dichroic mirror into the collimated beam, and thus is capable of taking images in two filter-bands simultaneously in imaging mode, or whole nearinfrared (0.9–2.5 µm) low-to-medium resolution multi-object spectra in spectroscopy (MOS) mode, both with a single exposure. SWIMS was carried into Subaru Telescope in 2017 for performance evaluation prior to completion of the construction of the 6.5 m telescope, and successfully saw the imaging first light in May 2018 and MOS first light in Jan 2019. After three engineering runs including the first light observations, SWIMS has been accepted as a new PI instrument for Subaru Telescope from the semester S21A until S22B. In this paper, we report on details of on-sky performance of the instrument evaluated during the engineering observations for a total of 7.5 nights.
‘Field Stacker’ is a unique system mounted on MIMIZUKU, a mid-infrared instrument for the TAO 6.5-m telescope. This system obtains a pair of distant targets simultaneously and aims at performing relative photometry with an accuracy of a few percent. A key to achieve the accurate relative photometry is precise flat fielding. We have developed a new method for the flat fielding using time variation of the sky background. We analyzed the data obtained in an engineering observation at the Subaru in 2018. The error of the flat fielding and the total error propagated from the flat fielding are estimated to be 0.2–0.3% and 0.5%, respectively.
The Mid-Infrared Multi-field Imager for gaZing at the UnKnown Universe (MIMIZUKU) is developed as the first-generation mid-infrared instrument for the University of Tokyo Atacama Observatory (TAO) 6.5-m telescope. MIMIZUKU performs medium-band imaging and low-resolution spectroscopy in 2-38 microns and enables highest-spatial-resolution observations in the long-wavelength mid-infrared beyond 25 microns. In addition, MIMIZUKU has a unique opto-mechanical device called ‘Field Stacker’, which enables us to observe a distant (<25 arcminutes) pair of target and reference objects simultaneously and improves accuracy of atmospheric calibration. This function is expected to improve photometric accuracy and quality of spectroscopic data even in the long-wavelength mid-infrared regions, where the atmospheric absorption is severe. In 2018, engineering observations of MIMIZUKU were carried out at the Subaru telescope, and its first-light was successfully achieved. In the engineering observations, the imaging and spectroscopic functions in the mid-infrared wavelengths (7.6-25 microns) were confirmed to be working almost as expected, although the sensitivity is still worse than the background-limited performance by a factor of a few due to high readout noise. The Field Stacker was also confirmed to be working as expected. It is confirmed that the photometric instability can be reduced to a few percent by using Field Stacker even when the atmospheric transmittance varies by 10% in time. It is also confirmed that spectroscopic observations can be performed not only in 10-micron band but also in 20-micron band, where the spectroscopic observations are difficult even at the Mauna Kea site. We report the results of these on-sky performance evaluations.
Tomo-e Gozen (Tomo-e) is a wide field optical camera for the Kiso 1.05 m f/3.1 Schmidt telescope operated by
the University of Tokyo. Tomo-e is equipped with 84 chips of front-illuminated CMOS image sensors with a
microlens array. The field of view is about 20 square degrees and maximum frame rate is 2 fps. The CMOS
sensor has 2160x1200 pixels and a size of pixel is 19 microns, which is larger than those of other CMOS sensors.
We have evaluated performances of the CMOS sensors installed in Tomo-e. The readout noise is 2.0 e- in 2 fps
operations when an internal amplifier gain is set to 16. The dark current is 0.5 e-/sec/pix at room temperature, 290K, which is lower than a typical sky background flux in Tomo-e observations, 50 e-/sec/pix. The efficiency
of the camera system peaks at approximately 0.7 in 500 nm.
Time variation of the atmospheric water vapor is an important problem to achieve accurate photometry in ground-based mid-infrared observations. Long-term (~ minutes or hours) variation has been already known, but short-term (~ seconds) variation has not been quantified in previous studies. We evaluate this short-term variation and the photometric error in the mid-infrared observations at the TAO site by using actual astronomical data. Estimated photometric errors are typically less than 1% but show 2-5% in two of fifteen cases. This suggests that the short-term variation of the water vapor is one of the factors which limit the photometric accuracy in ground based mid-infrared observations.
The Tomo-e Gozen is a wide-field high-speed camera for the Kiso 1.0-m Schmidt telescope, with a field-of-view of 20.7-deg2 covered by 84 chips of 2k x 1k CMOS image sensors with 19-μm pixels. It is capable to take consecutive images at 2-fps in full-frame read with an absolute time accuracy of 0.2 millisecond. The sensors are operated without mechanical coolers owing to a low dark current at room temperature. A low read noise of 2-e- achieves higher sensitivity than that with a CCD sensor in short exposures. Big data of 30-TBytes per night produced in the 2-fps observations is processed in real-time to quickly detect transient events and issue alerts for follow-ups.
The Simultaneous-color Wide-field Infrared Multi-object Spectrograph, SWIMS, is a first-generation near-infrared instrument for the University of Tokyo Atacama Observatory (TAO) 6.5m Telescope now being constructed in northern Chile. To utilize the advantage of the site that almost continuous atmospheric window appears from
0.9 to 2.5 μm, the instrument is capable of simultaneous two-color imaging with a field-of-view of 9.′6 in diameter or λ/▵λ 1000 multi-object spectroscopy at 0.9–2.5 μm in a single exposure. The instrument has been trans- ported in 2017 to the Subaru Telescope as a PI-type instrument for carrying out commissioning observations before starting science operation on the 6.5m telescope. In this paper, we report the latest updates on the instrument and present preliminary results from the on-sky performance verification observations.
MIMIZUKU (Mid-infrared Multi-field Imager for gaZing at the UnKnown Universe) is a near- to mid-infrared camera for the 6.5-m TAO (The university of Tokyo Atacama Observatory) telescope. To realize both the compactness of the instrument and the wide field of view of 2 arcmin, MIMIZUKU has unique reflective optics, which is composed of off-axis aspherical mirrors made of machined aluminum. These mirrors should be placed and aligned very precisely with the accuracy of < 0.01 mm and < 0.01 degrees. We performed the experiments to test whether MIMIZUKU optics works as designed at cryogenic temperature. We present the evaluation of imaging performance and the distortion on the focal plane of MIMIZUKU.
The Mid-Infrared Multi-field Imager for gaZing at the UnKnown Universe (MIMIZUKU) is a mid-infrared camera and spectrograph developed as a first-generation instrument on the University of Tokyo Atacama Observatory (TAO) 6.5-m telescope. MIMIZUKU covers a wide wavelength range from 2 to 38 μm and has a unique optical device called Field Stacker which realizes accurate calibration of variable atmospheric transmittance with a few percent accuracy. By utilizing these capabilities, MIMIZUKU realizes mid-infrared long-term monitoring, which has not been challenged well. MIMIZUKU has three optical channels, called NIR, MIR-S, and MIR-L, to realize the wide wavelength coverage. The MIR-S channel, which covers 6.8–26 μm, has been completed by now. We are planning to perform engineering observations with this channel at the Subaru telescope before the completion of the TAO 6.5-m telescope. In this paper, we report the results of the laboratory tests to evaluate the optical and detector performances of the MIR-S channel. As a result, we confirmed a pixel scale of 0.12 arcsec/pix and a vignetting- free field of view of 2./0 1./8. The instrument throughputs for imaging modes are measured to be 20–30%. Those for N - and Q -band spectroscopy modes are 17 and 5%, respectively. As for the detector performance, we derived the quantum efficiency to be 40–50% in the mid-infrared wavelength region and measured the readout noise to be 3000–6000 electrons, which are larger than the spec value. It was found that this large readout noise degrades the sensitivity of MIMIZUKU by a factor of two.
Simultaneous-color Wide-field Infrared Multi-object Spectrograph, SWIMS, is one of the first generation instruments for University of Tokyo Atacama Observatory 6.5m Telescope where almost continuous atmospheric window from 0.9 to 2.5μm appears, thanks to the high altitude and dry climate of the site. To utilize this excellent condition, SWIMS is capable of simultaneous two-color imaging with a field of view of 9’. in diameter and λ/Δλ ~1000 multi-object spectroscopy at 0.9–2.5μm in a single exposure, utilizing a dichroic mirror inserted in the collimated beam. Here, we overview the instrument, report results of its full-assembly tests in the laboratory and present the future plan.
MIMIZUKU is the first-generation mid-infrared instrument for the university of Tokyo Atacama Observatory (TAO) 6.5-m telescope. MIMIZUKU provides imaging and spectroscopic monitoring capabilities in a wide wavelength range from 2 to 38 μm, including unique bands like 2.7-μm and 30-μm band. Recently, we decided to add spectroscopic functions, KL-band mode (λ= 2.1-4.0 μm; R =λ/Δλ ~ 210) and 2.7-μm band mode ( λ= 2.4-2.95 μm; R ~ 620), and continuous spectroscopic coverage from 2.1 to 26 μm is realized by this update. Their optical designing is completed, and fabrications of optical elements are ongoing. As recent progress, we also report the completion of the cryogenic system and optics. The cryogenic system has been updated by changing materials and structures of thermal links, and the temperatures of the optical bench and detector mounting stages finally achieved required temperatures. Their stability against instrument attitude is also confirmed through an inclination test. As for the optics, its gold-plated mirrors have been recovered from galvanic corrosion by refabrication and reconstruction. Enough image quality and stability are confirmed by room-temperature tests. MIMIZUKU is intended to be completed in this autumn, and commissioning at the Subaru telescope and scientific operations on the TAO telescope are planned in 2017 and around 2019, respectively. In this paper, these development activities and future prospects of MIMIZUKU are reported.
The Tomo-e Gozen is an extremely wide-field optical camera for the Kiso 1.0-m Schmidt telescope. It is capable of taking consecutive frames with a field-of-view of 20 deg2 and a sub-second time-resolution, which are achieved by 84 chips of 2k×1k CMOS sensor. This camera adopts unconventional designs including a lightweight structure, a nonvacuumed and naturally-air cooled system, front-side-illuminated CMOS sensors with microlens arrays, a sensor alignment along a spherical focal plane of the telescope, and massive readout electronics. To develop technical components necessary for the Tomo-e Gozen and confirm a feasibility of its basic design, we have developed a prototype-model (PM) of the Tomo-e Gozen prior to the final-model (FM). The Tomo-e PM is equipped with eight chips of the CMOS sensor arranged in a line along the RA direction, covering a sky area of 2.0 deg2. The maximum frame rate is 2 fps. The total data production rate is 80 MByte sec-1 at 2 fps, corresponding to approximately 3 TByte night-1. After laboratory testing, we have successfully obtained consecutive movie data at 2 fps with the Tomo-e PM in the first commissioning run conducted in the end of 2015.
KEYWORDS: Phase modulation, Cameras, CMOS sensors, Data storage, Data processing, Computing systems, Signal detection, Observatories, Data acquisition, Astronomy
The Tomo-e Gozen camera is a next-generation, extremely wide field optical camera, equipped with 84 CMOS sensors. The camera records about a 20 square degree area at 2 Hz, providing “astronomical movie data”. We have developed a prototype of the Tomo-e Gozen camera (hereafter, Tomo-e PM), to evaluate the basic design of the Tomo-e Gozen camera. Tomo-e PM, equipped with 8 CMOS sensors, can capture a 2 square degree area at up to 2 Hz. Each CMOS sensor has about 2.6 M pixels. The data rate of Tomo-e PM is about 80 MB/s, corresponding to about 280 GB/hour. We have developed an operating system and reduction softwares to handle such a large amount of data. Tomo-e PM was mounted on 1.0-m Schmidt Telescope in Kiso Observatory at the University of Tokyo. Experimental observations were carried out in the winter of 2015 and the spring of 2016. The observations and software implementation were successfully completed. The data reduction is now in execution.
MIMIZUKU is a mid-infrared imager and spectrograph being developed for the University of Tokyo Atacama Observatory (TAO) 6.5-m telescope (PI: Y. Yoshii). To fully utilize a high atmospheric transmission of the Chajnantor site, MIMIZUKU covers a wide wavelength range from 2 to 38 μm with three array detectors: a HAWAII-1RG HgCdTe 1024 × 1024 array with a 5 μm cutoff manufactured by Teledyne, an Aquarius Si:As IBC 1024 × 1024 array by Raytheon, and a MF-128 Si:Sb BIB 128 × 128 array by DRS. We have newly developed an array controller system to operate these multiple arrays. A sampling rate higher than 0.5 MHz is required to prevent from saturation of their wells in broad-band imaging observations with MIMIZUKU due to high thermal background flux. Such high speed signals are dulled when passing through lines from the arrays to readout circuits. To overcome this problem, we have developed high-speed cryogenic buffer pre-amplifier circuits with commercial GaAs MESFETs, instead of Si JFETs, which are generally used in buffer amplifiers at cryogenic temperatures. The cryogenic buffer circuits are installed on an outer wall of the optical bench of MIMIZUKU at 20 K. We have measured readout noises of the array controller system including the cryogenic buffers in a test cryostat and room temperature circuits and confirmed that input referred noises of the system are lower than the specification value of the readout noise of the Aquarius array.
Strong time variation of atmospheric transmittance is a crucial problem for monitoring observations at mid- infrared wavelengths from the ground. To overcome this problem, a new device called "Field Stacker" has been developed. It is an optical device to combine two discrete fields in the telescope FoV into a single field and feed it in the camera. It enables us to observe a science target and a reference star simultaneously, and improve the photometric accuracy dramatically based on real-time calibration. To practically achieve highly accurate photometry, the tilt of the mirrors in the Field Stacker should be accurately adjusted. Acceptable error of the misalignment of each pick-up mirror is estimated to be < 0.0085 deg from a simple geometric calculation. The actual tilt error measured in the laboratory almost met this requirement. Spatial variation of the water vapor in the atmosphere is another concern for the accurate photometry. Assuming a simple model of the atmospheric structure, the spatial variation was estimated from time variation of infrared background radiation. The estimated variation of the water vapor was 0.00036 mm within the telescope FoV (Φ25 arc- minutes), suggesting that it does not significantly affect the photometric accuracy even at 31 and 37 μm. Number density of reference stars was examined based on all-sky infrared catalogues to estimate the availability of the Field Stacker. The estimated availabilities at 9 and 18 μm were 99.8% and 58.8%, respectively.
A cold chopper is a key device for next generation mid-infrared instruments such as TMT/MICHI. It should achieve fast and accurate position switching with a large chopping throw at cryogenic temperature. To satisfy the requirements, voice coil motors using superconducting MgB2 wire have been developed. We have made a first prototype of the VCM and carried out its performance measurements such as a transition temperature, transfer functions, and power dissipation in the laboratory. The results are almost consistent with the expectations and the calculations, but some show significant inconsistency. We have also made a next prototype which is small to fit the size of the MICHI chopper. This will be installed to a developing mid-infrared instrument MIMIZUKU and used for actual observations.
Anti-reflection (AR) is very important for high-throughput optical elements. The durability against cooling is
required for the AR structure in the cryogenic optics used for mid-infrared astronomical instruments. Moth-eye structure is a promising AR technique strong against cooling. The silicon lens and grism with the moth-eye structure are being developed to make high-throughput elements for long-wavelength mid-infrared instruments. A double-sided moth-eye plano-convex lens (Effective diameter: 33 mm, Focal length: 188 mm) was fabricated. By the transmittance measurement, it was confirmed that its total throughput is 1.7± 0.1 times higher than bare silicon lenses in a wide wavelength range of 20{45 μm. It suggests that the lens can achieve 83±5% throughput in the cryogenic temperature. It was also confirmed that the moth-eye processing on the lens does not modify the focal length. As for the grism, the homogeneous moth-eye processing on blaze pattern was realized by employing spray coating for the resist coating in EB lithography. The silicon grism with good surface roughness was also developed. The required techniques for completing moth-eye grisms have been established.
Simultaneous Color Wide-field Infrared Multi-object Spectrograph, SWIMS, is one of the first generation in- struments for the University of Tokyo Atacama Observatory (TAO) 6.5m Telescope now under construction. A dichroic mirror being inserted in the collimated beam, it is capable of two-color simultaneous imaging with FoV
of 9:16φ or R ∼ 1000 multi-object spectroscopy at 0.9–2.5μm wavelength range in one shot, and enables us to
carry out efficient NIR imaging/spectroscopic survey of objects such as distant galaxies and young stellar objects.
All the major components have been fabricated and we will start integration and laboratory cool-down test in the summer of 2014. After the engineering and initial science observations at the Subaru telescope, SWIMS will be transported to TAO telescope and see the first light in 2018.
The MIMIZUKU is the first-generation mid-infrared instrument for the TAO 6.5-m telescope. It challenges to prove the origin of dust and the formation of planets with its unique capabilities, wide wavelength coverage and precise calibration capability. The wide wavelength coverage (2-38 μm) is achieved by three switchable cameras, NIR, MIR-S, and MIR-L. The specifications of the cameras are revised. A 5μm-cutoff HAWAII-1RG is decided to be installed in the NIR camera. The optical design of the MIR-L camera is modified to avoid detector saturation.
Its final F-number is extended from 5.2 to 10.5. With these modifications, the field of view of the NIR and MIR-L camera becomes 1.2’ × 1.2’ and 31” × 31”, respectively. The sensitivity of each camera is estimated based on the
revised specifications. The precise calibration is achieved by the “Field Stacker” mechanism, which enables the simultaneous observation of the target and the calibration object in different fields. The up-and-down motion
of the cryostat (~ 1 t), critical for the Field Stacker, is confirmed to have enough speed (4 mm/s) and position accuracy (~ 50 μm). A control panel for the Field Stacker is completed, and its controllers are successfully
installed. The current specifications and the development status are reported.
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.
ANIR (Atacama Near InfraRed camera) is a near infrared camera for the University of Tokyo Atacama 1.0m telescope installed at the summit of Co. Chajnantor (5640m altitude) in northern Chile. The high altitude and the extremely low water vapor (precipitable water vapor:PWV=0.5mm) of the site enables us to perform observation of hydrogen Paschen alpha (Paα) emission line at 1.8751 μm. Since the first light observation in June 2009, we have succesfully obtained Paα narrow-band images of Galactic objects and near-by Galaxies. However, as there are many atmospheric absorption features within the wavelength range of the narrow-band filters which vary temporally due to change of PWV, it is difficult to calibrate the emission line flux accurately. Therefore, we have developed a new method to restore Paα emission-line flux from ground-based narrow-band filter imaging observations. First, average atmospheric transmittance within the narrow-band filter is derived using 2MASS stars in a image. Second, PWV is then estimated by comparing the transmittance with that calculated by atmospheric transmittance model software, ATRAN. Finally, the atmospheric transmittance at the wavelength of Paα emission-line is obtained from the model atmosphere corresponding to the obtained PWV. By applying this method to the data of nearby Luminous Infrared Galaxies obtained by ANIR, the emission line strength is estimated within the accuracy of 10% relative to that observed by HST/NICMOS. In this paper, we describe details of the calibration method and its accuracy.
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.
We successfully carried out 30-micron observations from the ground-based telescope for the first time with our newly
developed mid-infrared instrument, MAX38, which is mounted on the University of Tokyo Atacama 1.0-m telescope
(miniTAO telescope). Thanks to the high altitude of the miniTAO (5,640m) and dry weather condition of the Atacama
site, we can access the 30-micron wavelength region from ground-based telescopes. To achieve the observation at 30-
micron wavelength, remarkable devices are employed in MAX38. First, a Si:Sb 128x128 array detector is installed
which can detect long mid-infrared light up to 38-micron. Second, we developed metal mesh filters for 30-micron region
band-pass filter, which are composed of several gold thin-films with cross-shaped holes. Third, a cold chopper, a 6-cm
square plane mirror controlled by a piezoelectric actuator, is built into the MAX38 optics for canceling out the
atmospheric turbulence noise. It enables square-wave chopping with a 50-arcsecound throw at a frequency more than 5-
Hz. Finally, a low-dispersion grism spectrometer (R~50) will provide information on the transmission spectrum of the
terrestrial atmosphere in 20 to 40 micron. In this observation, we clearly demonstrated that the atmospheric windows
around 30-micron can be used for the astronomical observations at the miniTAO site.
We have developed a near infrared camera called ANIR (Atacama Near InfraRed camera) for the University of
Tokyo Atacama 1.0m telescope installed at the summit of Co. Chajnantor (5640m altitude) in northern Chile.
The camera is based on a PACE HAWAII-2 array with an Offner relay optics for re-imaging, and field of view
is 5.
3 × 5.
3 with pixel scale of 0.
31/pix. It is also capable of optical/infrared simultaneous imaging by inserting
a dichroic mirror before the focal plane. The high altitude and extremely low water vapor (PWV=0.5mm) of
the site enables us to perform observation of hydrogen Paschenα (Paα) emission line at 1.8751 μm. The first
light observation was carried out in July 2009, and we have successfully obtained Paα images of the Galactic
center using the N1875 narrow-band filter. This is the first success of Paα imaging of a Galactic object from a
ground based telescope. System efficiencies for the broad-band filters are measured to be 15% at the J-band and
30% at Ks, while that of the N1875 narrow-band filter, corresponding to Paα; wavelength, varies from 8 to 15%,
which may be caused by fluctuation of the atmospheric transmittance. ATRAN simulation suggests that this
corresponds to PWV of 0.3 - 1.5mm, consistent with previous results of the site testing. Measured seeing size
is median ~0.
8, corresponding to the real seeing value of 0.
6 - 0.
8. These results demonstrates the excellent
capability of the site for infrared observations.
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