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The telescope of the University of Tokyo Atacama Observatory has a primary mirror with a diameter in 6.5m. In order to fabricate the reflecting film initially on the mirror surface and to maintain its optical performance over a long period, a mirror{coating facility will be installed in operation building beside enclosure of the telescope at the summit of Co. Chajnantor (5,640m). The facility consists of mirror coating chamber, cleaning unit for stripping off the old film and clean-up the mirror, and a cart with a lifter for handling the primary mirror cell. Almost all equipment, including the main chamber, was completed by early 2020 and engaged as a mirror coating facility. In order to optimize the coating parameters, comprehensive performance tests were carried out (without primary mirror cell which plays a role of a part of chamber). The evaluation items are how long it takes to reach the target vacuum level and parameters of the current, voltage, and application time during ion bombardment and aluminization. Through iterating test, we were able to obtain each parameter that ultimately met the requirements of the TAO telescope mirror.

The University of Tokyo Atacama Observatory Project is to construct a 6.5 m infrared-optimized telescope at the summit of Co. Chajnantor (5640 m altitude) in northern Chile. The telescope optics uses a Ritchey-Chretien type layout, with an under-sized secondary mirror to reduce stray light caused by thermal emission from the telescope structure. The primary mirror is a F/1.25 lightweight borosilicate glass (Ohara E6) mirror with honeycomb structure, which is developed by Steward Observatory Richard F. Caris Mirror Lab. The telescope has two Nasmyth foci and two folded-Cassegrain foci, which can be switched by rotating a tertiary mirror. The final focal ratio is 12.2 with a field of view of 25 arcmin in diameter. The telescope mount is a tripod-disk alt-azimuth mount. Both the azimuth and elevation axes are supported by and run on hydrostatic bearings, and they are driven by friction drives with servo motors, which are controlled by the telescope control system. It also controls the hexapod mount of the secondary mirror and the pneumatic actuators of the primary mirror support to keep good image quality during the observation. An off-axis Shack-Hartmann sensor installed in each focus measures the wavefront aberration of the telescope optics, then the misalignment between the secondary and primary mirrors is corrected by adjusting the hexapod mount while other aberrations are corrected by the deformation of the primary mirror. The force distribution of the actuators for correction will be calculated by fitting the wave-front errors with a series of bending modes of the primary mirror.

Institute of Astronomy, Graduate School of Science, the University of Tokyo is promoting the University of Tokyo Atacama Observatory Project, which is to construct an infrared-optimized 6.5m telescope at the summit of Co. Chajnantor (5640m altitude) in northern Chile. The high altitude and dry climate (PWV-0.5mm) realize transparent atmosphere in the infrared wavelength. The project is now approaching the final phase of the construction. Production of major components are almost completed: Production and preassembly test of a telescope mount and dome enclosure have been completed in Japan, and they are being transported to Chile. Three mirrors, the 6.5m primary, 0.9m secondary, and 1.1m-0.75m tertiary mirrors and their support systems have been all completed and tested in the USA. An aluminizing chamber have been fabricated in China, and its tests have been carried out in Japan. Development of two facility instruments, SWIMS and MIMIZUKU, are also completed. They were transported to the Subaru telescope, successfully saw the first light in 2018, and are confirmed to have the performance as designed. On-site construction work at the summit is now underway. Expansion of a summit access road from the ALMA concession was completed in 2019. Installation of foundation will follow, and then erection of the dome enclosure and a control building. The construction works are delayed by COVID-19, and we expect to complete the dome enclosure by Q3 of 2021. The telescope will be installed inside the dome and see the engineering first light by early 2022.

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.

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 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.

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.

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 telescope of the University of Tokyo Atacama Observatory has a primary mirror with a diameter in 6.5m. In order to fabricate the reflecting film initially on the mirror surface and to maintain its optical performance over a long period, we have a mirror-coating facility being installed at the summit of Co. Chajnantor (5,640m). The facility consists of a clean booth for stripping off the old film, a mirror coating chamber, and a cart with a lifter for handling the primary mirror. A conventional evaporation system with a metal pre-wetted filament array is adopted for achieving various optical requests. Among the many development items, the fabrication of the transportation and lifting cart has been already completed. It has efficient performance in load capacity (>60 tons) and maximum lifting height (1,750 mm). A cleaning machine having injection nozzles that can realize an efficient and safe cleaning sequence also been completed. A test of the evaporation system using dedicated filaments and filament boxes, which are customized to the TAO's requirements, has shown a uniform coating on a test mirror. An array pattern of the filaments has also been decided based on the coating tests to satisfy the optical specification of the telescope. A detailed design of the main chamber has been almost completed, it is only waiting for the production in the near future.

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/uλ 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.

A basic design of enclosure and support facilities for the University of Tokyo Atacama observatory (TAO) 6.5-m telescope is described in this paper. The enclosure facility has a carousel shape with an open-space near the ground surface. The upper carousel rotates independently of the telescope. Horizontally opened slit doors, a dozen ventilation windows, wind and moon shields, and an overhead bridge-crane are equipped. For safety reasons, most of maintenance walkways are placed inside of the enclosure facility. An observation floor of the enclosure facility is connected to the support facility via a bridge for maintenance of observation instruments and a primary mirror of the telescope. Air inside of the enclosure and support facilities is exhausted to an underground tunnel.

The telescope of the University of Tokyo Atacama Observatory has a 6.5-m primary mirror in diameter. In order to fabricate the reflecting film initially and to maintain its performance over a long period, we have mirror coating facility on site. We have chosen to leave the primary mirror in its cell with the mirror support system intact. Two major advantages of leaving the mirror in its cell are that the mirror does not have to be lifted or handled and the support system does not have to be removed or reinstalled for coating. The facility consists of a clean booth for stripping of the old film, an evaporation coating chamber, and a cart with a lifter for handling the primary mirror. A conventional evaporation system with a metal pre-wetted filament array is adopted for achieving various optical requests. The coating equipment has also a function of fabrication for film on secondary and tertiary mirrors.

We here summarize the design and the current fabrication status for the University of Tokyo Atacama Observatory (TAO) 6.5-m telescope. The TAO telescope is operated at one of the best sites for infrared observations, at the summit of Co. Chajnantor in Chile, and is optimized for infrared observations. The telescope mount, mirrors, and mirror support systems are now at the final design phase. The mechanical and optical designs are done by following and referring to those of the Magellan telescopes, MMT, and Large Binocular Telescope. The final focal ratio is 12.2. The field-of-view is as wide as 25 arcmin in diameter and the plate scale is 2.75 arcsec mm −1 . The F/1.25 light-weighted borosilicate (Ohara E6) honeycomb primary mirror is adopted and being fabricated by the Steward Observatory Mirror Laboratory. The primary mirror is supported by 104 loadspreaders bonded to the back surface of the mirror and 6 adjustable hardpoints. The mirror is actively controlled by adjusting the actuator forces based on the realtime wavefront measurement. The actuators are optimized for operation at high altitude of the site, 5640-m above the sea level, by considering the low temperature and low air pressure. The mirror is held in the primary mirror cell which is used as a part of the vacuum chamber when the mirror surface is aluminized without being detached from the cell. The pupil is set at the secondary mirror to minimize infrared radiation into instruments. The telescope has two Nasmyth foci for near-infrared and mid-infrared facility instruments (SWIMS and MIMIZUKU, respectively) and one folded-Caseggrain focus for carry-in instruments. At each focus, autoguider and wavefront measurement systems are attached to achieve seeing-limited image quality. The telescope mount is designed as a tripod-disk type alt-azimuth mount. Both the azimuthal and elevation axes are supported by and run on the hydrostatic bearings. Friction drives are selected for these axis drives. The telescope mount structure and primary mirror support as well as the mirrors are under thermal control and maintained at ambient air temperature to minimize the mirror seeing.

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.

TAO (The University of Tokyo Atacama Observatory) is planned to be constructed at the summit of Co. Chajnantor (5640 m altitude) in Chile. MIMIZUKU (Mid-Infrared Multi-field Imager for gaZing at the UnKnown Universe) is a mid-infrared imager (Field of View: 1' x 1'- 2' x 2') and spectrometer (Δλ/λ: 60-230) for the 6.5-m TAO telescope, covering the wavelength range of 2-38 μm. The MIMIZUKU has a unique equipment called Field Stacker (FS) which enables the simultaneous observation of target and reference object. The simultaneity is expected to improve photometric accuracy and to realize long-term monitoring observations. The development status of the MIMIZUKU is reported in this paper. The FS and the cryostat of the MIMIZUKU have been fabricated and under testing. The cold optics (550 mm x 750 mm x 2 floors) with 28 mirrors has been constructed. The mirrors were aligned with the positional precision of 0.1 mm and the angular precision of 0.1 deg. The evaluated optical performance is that the diffraction-limited image at λ

SWIMS (Simultaneous-color Wide-field Infrared Multi-object Spectrograph) is one of the first-generation instruments for the University of Tokyo Atacama Observatory (TAO; P.I.: Yuzuru Yoshii) 6.5-m telescope which is planned to be constructed at the world's highest site, the summit of Cerro Chajnantor (an altitude of 5,640 m or 18,500 ft) in northern Chile. By placing a dichroic mirror into the collimated beam, SWIMS is capable of wide-field (φ 9'.6 with 0".126 pixel-1) two-color simultaneous imaging as well as multi-object spectroscopy (MOS) using cooled multi-slit masks covering the entire near-infrared spectra between 0.9 and 2.5 μm in a single exposure with low-to-medium spectral resolutions. Up to 20 user-defined slit masks as well as long slit masks are available. The field of view is covered with four 2048 x 2048 pixel HgCdTe focal plane arrays (HAWAII-2RG). Tests of the MOS slit mask exchanger motions have been completed successfully without any trouble under cryogenic environment. Further MOS tests will be performed at various tilt and rotation angles of the instrument using a telescope simulator. Also, a conceptual study of a compact and cryogenic wide-field integral field spectroscopy unit handled by the slit mask exchanger is now being carried out. The part of the current designs is optimized for installation on the Subaru Telescope for performance verification and early scientific observations prior to the construction of the TAO 6.5-m telescope. In this paper, we present the design and development status of the instrument.

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.

We have evaluated on-sky performances of a mid-infrared camera MAX38 (Mid-infrared Astronomical eXploerer) on the miniTAO 1-meter telescope. A Strehl ratio at the N-band is estimated to be 0.7-0.8, and it reaches to 0.9 at the 37.7 micron, indicating that diffraction limited angular resolution is almost achieved at the wavelength range from 8 to 38 micron. System efficiencies at the N and the Q-band are estimated with photometry of standard stars. The sensitivity at the 30 micron cannot be exactly estimated because there are no standard stars bright enough. We use the sky brightness instead. The estimated efficiencies at the 8.9, 18.7, and 31.7 micron are 4%, 3%, 15% , respectively. One-sigma sensitivity in 1 sec integration of each filter is also evaluated. These give good agreements with the designed values. Preliminary scientific results are briefly reported.

Thirty micron has remained one of unexplored frontiers of ground-based astronomical observations. Recent developments of extreme high sites including the Chajnantor TAO site (5,640m) enable us to access the this wavelengths from the ground. The expected transmittance seems clear enough for astronomical observations, but practical evaluations based on astronomical data has not been carried out yet. We have analyzed images obtained at the 31.7 micron with a mid-infrared camera MAX38 attached on a mini-TAO 1.0-meter telescope. 109 images of a star IRC+10420 and 11,114 images of the sky have been reduced. Clear relationship between the measured photocurrents and the perceptible water vapor has been found. Simple estimation of the photocurrents with of the ATRAN model gives good agreements with the measurements, indicating that the ATRAN model reproduce the atmospheric transmittance reasonably well. This also supports our assumption that the scaling factor 0.85 of the PVW at the Chajnantor TAO site to the PWV at the APEX. The average transmittance in the 31.7 micron is achieved to be over 20% when the PWV below 0.6 mm. In some cases clear degradation up to 10% in the transmittance is found. It may be caused by droplets of liquid or iced water with a size over 10 micron although the causes are not exactly specified. Diurnal time variations of the sky photocurrents are also investigated. The sky is sometimes bright and usually unstable in the twilight time. On the other hand the sky around the noontime does not show clear difference from the night sky. It may suggest that the observing condition at the thirty micron windows remain good even in the daytime.

We describe the design and current status of a near-infrared multi-object spectrograph for the University of Tokyo Atacama Observatory (TAO) project, which is to construct a 6.5m infrared telescope on the summit of Co. Chajnantor (altitude of 5,460m) in the northern Chile. The instrument, named SWIMS (Simultaneous-color Wide-field Infrared Multi-object Spectrograph), covers a wavelength range from 0.9 to 2.5 μm with a field of view of 9.6 in diameter using 4096 × 4096 pixels with a pixel scale of 0.13 pixel-1. It has two observation modes: a wide-field imager and a multi-object spectrograph (MOS). The MOS mode adopts cooled multi-slit masks with 30 slits at a maximum, and achieves a spectral resolution of λ/uλ~ 1000. Up to 20 masks can be installed in a mask storage dewar. In both modes, two wavelength ranges of 0.9-1.4 μm and 1.4-2.5 μm are observed simultaneously with a dichroic mirror placed in the collimated beam. This will provide us data covering the wide spectral range under same conditions such as weather, telescope pointing, and so on. Such data are important not only for redshift surveys of distant galaxies but also for rapidly time-variable events such as gamma-ray bursts. As SWIMS is expected to be completed before the construction of the 6.5m telescope, we plan to carry out performance verification and early scientific observations on the Subaru Telescope at Hawaii.

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.

Ground-based mid-infrared observations have two distinct advantages over space observations despite relatively lower sensitivity. One is the high spatial resolution and the other is the monitoring capability. These advantages can be emphasized particularly for the next coming ground-based infrared project University of Tokyo Atacama Observatory (TAO). Thanks to the low water vapor of the TAO site (5,640m) and the large aperture of the telescope (6.5meter), we can observe at 30 micron with a spatial resolution of 1 arcsec. It is about ten times higher than that of current space telescopes. The TAO is also useful for monitoring observations because of the ample observing time. To take these advantages we are now developing a new mid-infrared infrared instrument for the TAO 6.5-meter telescope. This covers a wide wavelength range from 2 to 38 micron with three detectors (Si:As, Si:Sb, and InSb). Diffraction limited spatial resolution can be achieved at wavelengths longer than 7 micron. Low-resolution spectroscopy can also be carried out with grisms. This instrument equips a newly invented "field stacker" for monitoring observations. It is an optical system that consists of two movable pick-up mirrors and a triangle shaped mirror, and combine two discrete fields of the telescope into camera's field of view. It will enable us to apply a differential photometry method and dramatically improve the accuracy and increase the feasibility of the monitoring observations at the mid-infrared wavelengths.

We have been developing 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 major aim of this camera is to carry out an imaging survey in Paschen α emission line (1.8751μm) from the ground for the first time. The camera is based on a PACE-HAWAII2 array with an Offner relay optics for re-imaging, and field of view is 5.'3 × 5.'3 with pixel scale of 0."308/pix. It is scheduled to see first light in the end of 2008, and start the Paschen α/β survey of the Galactic plane in 2009.