A design of the wide-field infrared camera (AIRC) for Antarctic 2.5m infrared telescope (AIRT) is presented. The off-axis design provides a 7’.5 ×7’. 5 field of view with 0”.22 pixel-1 in the wavelength range of 1 to 5 μm for the simultaneous three-color bands using cooled optics and three 2048×2048 InSb focal plane arrays. Good image quality is obtained over the entire field of view with practically no chromatic aberration. The image size corresponds to the refraction limited for 2.5 m telescope at 2 μm and longer. To enjoy the stable atmosphere with extremely low perceptible water vapor (PWV), superb seeing quality, and the cadence of the polar winter at Dome Fuji on the Antarctic plateau, the camera will be dedicated to the transit observations of exoplanets. The function of a multi-object spectroscopic mode with low spectra resolution (R~50-100) will be added for the spectroscopic transit observation at 1-5 μm. The spectroscopic capability in the environment of extremely low PWV of Antarctica will be very effective for the study of the existence of water vapor in the atmosphere of super earths.
We have built a control system for a mini survey facility dedicated to photometric monitoring of nearby bright (K<5) stars in the near-infrared region. The facility comprises a 4-m-diameter rotating dome and a small (30-mm aperture) wide-field (5 × 5 sq. deg. field of view) infrared (1.0–2.5 microns) camera on an equatorial fork mount, as well as power sources and other associated equipment. All the components other than the camera are controlled by microcomputerbased I/O boards that were developed in-house and are in many of the open-use instruments in our observatory. We present the specifications and configuration of the facility hardware, as well as the structure of its control software.
Dome Fuji, on the Antarctic plateau, is expected to be one of the best sites for infra-red astronomy. In Antarctica, the coldest, driest air on Earth provides the deepest detection limit. Furthermore, the weak atmospheric turbulence above the boundary layer allows for high spatial resolution. We plan to perform site-testing at Dome Fuji during the austral summer of 2010-2011. This will be the first observation to use an optical/infra-red telescope at Dome Fuji. This paper introduces the Antarctic Infra-Red Telescope with a 40cm primary mirror (AIRT40) which will be used in this campaign; it is an infra-red Cassegrain telescope with a fork equatorial mount. AIRT40 will be used for not only site testing (measurement of seeing and sky background) and daytime astronomical observation during this summer campaign, but also for remote scientific observations during the 2012-2014 winter-over campaign. For this purpose, AIRT40 has to work well even at -80 degree Celsius. Therefore, we accounted for the thermal contraction of the materials while designing it, and made it with special parts which were tested in a freezer. For easy operation, many handles for transportation and a polar alignment stage were installed. Moreover, we confirmed that this telescope has enough pointing, tracking, and optical accuracy for the summer campaign through the test observations at Sendai, Japan. Because of these preparations AIRT40 is suited for observations at Dome Fuji. In the 2010-2011 campaign AIRT40 will be used to measure the seeing, infra-red sky background, and to observe Venus.
In Antarctica the cold and dry air is expected to provide the best observing conditions on the Earth for astronomical
observations from infra-red to sub-millimeter. To enjoy the advantages in Antarctica, we have a plan to make
astronomical observations at Dome Fuji, which is located at inland Antarctica. However, the harsh environment is very
problematic. For example, the temperature comes down to as low as-80 degree Celsius in winter, where instruments
designed for temperate environment would not work. In this context, we have developed a 40 cm infra-red telescope,
which is dedicated for the use even in winter at Dome Fuji. In designing the telescope, we took account of the difference
of the thermal expansion rate among materials, which were used for the telescope. Movable parts like motors were
lubricated with grease which would be effective at -80 degrees. Most parts of the telescope are made of aluminum to
make the telescope as light as possible, so that it makes the transportation from seacoast to inland and assembling at
Dome Fuji easier. We also report the experiment that we have done at Rikubetsu (the coldest city in Japan) in February
We present the development and first astronomical applications of VPH grisms which are now operated at
cryogenic temperature in MOIRCS, a Cassegrain near-infrared instrument of the Subaru Telescope. We designed
and fabricated the VPH grisms with a resolving power ~3000 for the use in near-infrared bands. The VPH
grating, encapsulated in BK7 glass, is glued between two ZnSe prisms with vertex angle of 20 deg. After
repeating several thermal cycles down to ~100 K carefully enough not to cause irreparable damage on the
grism during cooling, we evaluated the performance at cryogenic temperature in the laboratory and found no
deterioration and no large difference in the performance from that measured in room temperature. Based on
commissioning observations with MOIRCS, we have confirmed the high efficiency (~0.8) and the resolving power
of the original design. Common use of the grisms is due to start in the second semester of 2008.
This paper details the design process for AIR-C, the Antarctic Infra-Red Camera, for use with Tohoku University's 40
cm Antarctic telescope. The camera will also be compatible with the planned 2 meter class Japanese telescope at Dome
F. First, we review of the design requirements which shaped the development process. The optical chain receives the
most detailed discussion. The other components will be discussed briefly. The effect of cryogenic temperatures on the
lenses was taken into account during the design process. AIR-C's performance is predicted. Finally, we discuss the
scientific potential for a small Antarctic telescope.
We have successfully fabricated germanium immersion gratings with resolving power of 45,000 at 10 μm by using a nano precision 3D grinding machine and ELID (ELectrolytic In-process Dressing) method. However the method spends large amount of machine times. We propose grooves shape with a new principle for a solid grating, which
achieves high performance and lower cost. We have developed volume phase holographic (VPH) grisms with zinc selenide (ZnSe) prisms for spectrograph of the Subaru Telescope and the other telescopes. While a VPH grism with high index prisms achieves higher dispersion,
diffraction efficiency of VPH grating decreases toward higher orders. A "quasi-Bragg grating" which inherits advantage of a VPH grating achieves high diffraction efficiency toward higher orders. Wavelength tuners with a pair of counter-rotation prisms for a VPH and quasi-Bragg grating obtain high diffraction efficiency over wide wavelength range. The novel immersion grating, VPH grism with high index prisms, quasi-Bragg
grating and wavelength tuners dramatically reduce volumes of astronomical spectrographs.
The design, development, operation and current performance of MOS (multi-object spectroscopy) mode of MOIRCS is described. MOIRCS (Multi-Object Infrared Camera and Spectrograph) is one of the second-generation instruments for the Subaru Telescope and provides imaging and MOS modes with a 4' × 7' field of view for a wavelength range from 0.85 to 2.5 μm. To achieve near-infrared (NIR) MOS up to K-band, MOS mode uses multi-slit masks and a mask exchange system in a cryogenic environment. The masks are housed in a vacuum dewar attached to the MOIRCS main dewar and separated by a large gate valve. The mask dewar is equipped with its own cryogenic cooler and a vacuum pump and is capable of storing eighteen masks. The masks are made of thin aluminum foil. Slits are cut with a laser, with software that corrects for the effects of thermal contraction. The masks are cooled to below 130 K in the mask dewar and transported to the focal plane in the main dewar through the gate valve with a linear motion manipulator. An interlock is equipped on the mask exchange system to secure the cryogenic instrument from accident. Replacing masks can be done in the daytime without breaking the vacuum of the main dewar by isolating the mask dewar with the gate valve. Acquisition occurs by iteratively taking on-sky images through alignment holes on the mask until the rotation and offset between alignment stars and alignment holes become small enough. MOIRCS/MOS mode will be open to the public in late 2006.
MOIRCS is a new Cassegrain instrument of Subaru telescope, dedicated for wide field imaging and multi-object spectroscopy in near-infrared. MOIRCS has been constructed jointly by Tohoku University and the Subaru Telescope and saw the first light in Sept., 2004. The commissioning observations to study both imaging and spectroscopic performance were conducted for about one year. MOIRCS mounts two 2048 × 2048 HAWAII2 arrays and provides a field of view of 4' x 7' with a pixel scale of 0."117. All-lens optical design is optimized for 0.8 to 2.5 μm with no practical chromatic aberration. Observations confirm the high image quality over the field of view without any perceptible degradation even at the field edge. The best seeing we have obtained so far is FWHM=0."18. A novel design of MOIRCS enables us to perform multi-object spectroscopy with aluminum slit masks, which are housed in a carrousel dewar and cooled to ~ 110 K. When choosing MOS mode, a manipulator pulls out a slit mask from the carrousel into the MOIRCS main dewar and sets it properly at the Cassegrain focus. The carrousel is shuttered by a gate valve, so that it can be warmed and cooled independently to exchange slit-mask sets during daytime. We have tested various configurations of 30 or more multi-slit positions in various sky fields and found that targets are dropped at the centers of slits or guide holes within a dispersion of about 0.3 pixels (0."03). MOIRCS has been open to common use specifically for imaging observations since Feb. 2006. The MOS function will be available in next August.
MOIRCS (Multi-Object Infrared Camera and Spectrograph) is a new instrument for the Subaru telescope. In order to perform observations of near-infrared imaging and spectroscopy with cold slit mask, MOIRCS contains many device components, which are distributed on an Ethernet LAN. Two PCs wired to the focal plane array electronics operate two HAWAII2 detectors, respectively, and other two PCs are used for integrated control and quick data reduction, respectively. Though most of the devices (e.g., filter and grism turrets, slit exchange mechanism for spectroscopy) are controlled via RS232C interface, they are accessible from TCP/IP connection using TCP/IP to RS232C converters. Moreover, other devices are also connected to the Ethernet LAN. This network distributed structure provides flexibility of hardware configuration. We have constructed an integrated control system for such network distributed hardwares, named T-LECS (Tohoku University - Layered Electronic Control System). T-LECS has also network distributed software design, applying TCP/IP socket communication to interprocess communication. In order to help the communication between the device interfaces and the user interfaces, we defined three layers in T-LECS; an external layer for user interface applications, an internal layer for device interface applications, and a communication layer, which connects two layers above. In the communication layer, we store the data of the system to an SQL database server; they are status data, FITS header data, and also meta data such as device configuration data and FITS configuration data. We present our software system design and the database schema to manage observations of MOIRCS with Subaru.
We describe an optical design process and image performance evaluations for Multi-Object near-InfraRed Camera and Spectrograph (MOIRCS). MOIRCS is a near-infrared imager and multi-object spectrograph under construction for the Subaru Telescope. MOIRCS provides direct imaging of 4' x 7' F.O.V. with a pixel scale of 0.12". MOIRCS also provides low-resolution multi-object spectroscopy with grisms and cooled multi-slit masks on the Cassegrain focal plane. CaF2, BaF2, ZnSe, and Fused Silica are used as the lens materials. They have high transmission in the near-infrared wavelength. During the design process, we find that a triplet with an achromatic doublet and a ZnSe singlet shows good performance for chromatic aberration. Therefore, we design our optics on the basis of the triplet with ZnSe. The designed optics shows good performances. Ensquared energy within 2 pixel square is more than 85% over the entire wavelength range and F.O.V. We do not need refocusing with the change of observed wavelengths because chromatic aberration is as small as 100 μm by the triplet with ZnSe over the entire wavelength range from 0.85 to 2.5 μm. Lateral chromatic aberration of 15 μm is less than 1 pixel size. Detailed tolerance analysis is done with possible manufacturing and aligning errors considered. The result shows that designed performances will be kept with a probability of 80% with reasonable tolerances. Ghost analysis is also done over entire F.O.V. and we find a ghost image of 13 magnitude fainter than original image that is not significant for our purpose. Therefore, we conclude that we can obtain enough performances with designed optics.
We report on the results of the performance tests of the HAWAII-2 FPAs for Multi-Object Infra-Red Camera and Spectrograph (MOIRCS). MOIRCS provides wide-field imaging mode (4'x7' F.O.V.) and multi-object spectroscopy mode for the wavelength range from 0.85 to 2.5 μm. To achieve the wide field-of-view with the high angular resolution, we use two 2048 x 2048 HgCdTe FPAs, HAWAII-2. We have made performance tests of both the engineering-grade and the science-grade HAWAII-2 arrays. Array performances such as stability of bias frames, read noise and dark current are evaluated at the operating temperature of 78K. In addition, we search for the optimum well depth, readout speed by changing bias voltages. We have finished tests of the engineering-grade array and the performance of our science-grade arrays is under investigation.
TUFPAC (Tohoku University Focal Plane Array Controller) is an array control system originally designed for flexible control and efficient data acquisition of 2048 x 2048 HgCdTe (HAWAII-2) array. A personal computer operated by Linux OS controls mosaic HAWAII-2s with commercially available DSP boards installed on the PCI bus. Triggered by PC, DSP sends clock data to front-end electronics, which is isolated from the DSP board by photo-couplers. Front-end electronics supply powers, biases and clock signals to HAWAII2. Pixel data are read from four outputs of each HAWAII2 simultaneously by way of four channel preamps and ADCs. Pixel data converted to 16 bit digital data are stored in the frame memory on the DSP board.
Data are processed in the memory when necessary. PC receives the frame data and stores it in the hard disk of PC in FITS format. A set of the DSP board and front-end electronics is responsible for controlling each HAWAII-2. One PC can operate eight mosaic arrays at most. TUFPAC is applicable to the control of CCDs with minor changes of front-end electronics.
MOIRCS (Multi-Object InfraRed Camera and Spectrograph) is one of the second generation instruments for the Subaru Telescope. This instrument is under construction by the National Astronomical Observatory of Japan and Tohoku University. It has imaging and multi-object spectroscopy (MOS) capabilities in the wavelength range from 0.85 μm to 2.5 μm with 4' x 7' F.O.V. The focal plane is imaged onto two 2048 x 2048 pixel HAWAII-2 HgCdTe arrays with a pixel scale of 0."12 pixel-1 through two independent optical trains. The optical design is optimized to maximize K band performance. Unique design of MOIRCS allows multi-object spectroscopy out to K band with cooled multi-slit masks. Twenty-four masks are stored in a mask dewar and are exchanged in the cryogenic environment. The mask dewar has its own vacuum pump and cryogenic cooler, and the masks can be assessed without breaking the vacuum of the main dewar. The two-channel optics and arrays are mounted back-to-back of a single optical bench plate. A PC-Linux based infrared array control system has been prepared to operate HAWAII-2. The first light of MOIRCS is planned in the spring of 2003.
We use the HAWAII-2 (2048 × 2048 HgCdTe) FPAs in MOIRCS (Multi-Object Infra-Red Camera and Spectrograph) for the astronomical use on the Subaru telescope. MOIRCS, which is currently being constructed by Tohoku University and the National Astronomical Observatory of Japan, is one of the second generation instruments for Subaru. It will provide the wide-field imaging mode (4 × 7 arcmin2) and the multi-object spectroscopy mode with the wavelength range of 0.8 to 2.5 μm.
To achieve the large field of view with the high spatial resolution, we use two large-format near-infrared arrays, HAWAII-2. We have developed an infrared array control system specially designed for flexible control and efficient data acquisition of the HAWAII-2 arrays. The array control system, TUFPAC, consists of a personal computer operated by LINUX OS and commercially available DSP boards. By using TUFPAC and the cryostat for array tests, we have made tests of the HAWAII-2 array. In this paper, we report on our array control system and the results of various performance tests for the HAWAII-2 array.
To built a 3K X 3K pixel near-IR FPA, we have made a package and a multi-chip module for Mitsubishi 1040 X 1040 PtSi CSD, which is one of the largest SWIR FPAs. Mosaicing demands smallest gaps between chips to achieve a large fill-factor and controlled flatness to fit a camera focal plane. The package of 52-pin half-pitch PGA has been designed to be smaller than the bear chip. After the chip is glued on the package and wire-bonded, nine packages with the chip are arrayed in three by three on a multi chip module (MCM) of 6 cm X 6 cm area. The fill-factor of the imaging area is 89 percent. The package and MCM are made of AlN ceramic of high thermal conductivity. MCM, therefore, plays a role of an efficient heat sink. The surface of the package, with which the chip is in contact, has been polished with accurate flatness as well as MCM. As the result, the height of nine chips built on MCM are uniform within approximately 20 micrometers in 6 cm X 6 cm area. The mosaic array will be equipped in a near-IR camera for astronomical observations of a wide field view.
We present the performance of the 1040 by 1040 PtSi CSD manufactured by Mitsubishi Electric Co. for an application of astronomical imaging. The sensor was evaluated both in laboratory and in real observing conditions. The results of noise, quantum efficiency, linearity, dark current and photometric accuracy are presented.
A new infrared camera equipped with a 1040 by 1040 PtSi CSD array is in operation as a common-use instrument at Kiso Observatory of the University of Tokyo. The camera attached to the prime focus (F/3.1) of the 105 cm Schmidt telescope gives a field of view of 18'.4 by 18'.4 with a spatial resolution f 1'.1 per pixel. The image resolution, detection limit, and other performances in an astronomical application are presented. Based on the observations of nearby galaxies and Galactic objects, we demonstrate that the camera is very powerful for wide-field imaging in astronomy.
We have constructed a near-infrared camera with a 1040 by 1040 PtSi CSD array for astronomical use. The camera is attached to the prime focus (f/3.1) of the 105 cm Schmidt telescope at Kiso observatory. The field of view is 18.4 by 18.4 arcmin2 and the spatial resolution is 1.06 by 1.06 arcsec2/pixel. The camera can be used mainly in J ((lambda) eff equals 1.25 micrometer), H (1.65 micrometer), and K' (2.15 micrometer) bands. Since thermal emissions from the atmosphere and room-temperature bodies are main background noise sources in the near-infrared, we designed a cold baffle inside the camera to minimize the effect of the thermal radiation from the telescope. Both the charge transfer efficiency and the dark current of PtSi arrays are sensitive to the array temperature. Therefore we carefully control the temperature at 60 +/- 0.05 K by using a refrigerator and a temperature controller. The readout noise was reduced to 70 e by adopting a correlated multiple sampling technique. The array response was linear within 0.7% accuracy below 25% of the full well capacity (< 4.0 X 105 e).