Measurement of the alignment error of the telescope mirrors is an essential and demanding task in the telescope assembly phase. One method is to examine the aberration over the whole telescope field of view from sky images with stars, but there are complicated issues in the case of large telescopes. The focal plane of the University of Tokyo Atacama Observatory (TAO) 6.5-m telescope has a large diameter of 546mm and a field curvature. Therefore, many imaging sensors must be arrayed on the curved focal plane. We propose a concept of a screen camera for the TAO 6.5-m telescope. To lower the cost, we accept the degradation of the spatial resolution up to ∼2 arcseconds and the decrease in optical throughput. This system consists of a transparent screen, a camera lens, and a CMOS sensor, and it obtains sky images through the telescope on the screen. The transparent spherical screen with one side sanded is placed at the telescope focal plane. A CMOS sensor with a commercially available camera lens and filters is placed at about 1.5 meters from the screen and captures the starry sky on the screen. The pixel scale on the CMOS sensor is calculated to be 0.31 arcseconds, and the estimated limiting magnitude is about 13 in a 10-second exposure at a 10σ level. After the telescope mirror alignment, the screen camera will provide focused sky images in the whole field of view, 25 arcminutes diameter.
The University of Tokyo Atacama Observatory (TAO) is a project to build and operate a 6.5m telescope at the summit of Co. Chajnantor (5640 m.a.s.l). This is promoted by the Institute of Astronomy, School of Science, the University of Tokyo in collaboration with many institutes and universities in Japan and Chile. The site construction started in 2018 and was successfully completed by April 2024. An operation support building and an enclosure have already been constructed and are operational at the summit. Electricity is supplied by two generators installed in the operations building. The telescope mount and mirrors have already completed their tests in Japan and the U.S., respectively. They were transported to Chile and wait for the assembly. The first light instruments, NICE and MIMIZUKU, are undergoing final adjustment in Japan and will be transported to Chile as the telescope assembly progresses. The near-infrared instrument SWIMS has completed its open use on the Subaru telescope and returned back to Japan in Aug. 2023 for upgrading for TAO. The near-infrared spectrograph TARdYS, which is being developed in collaboration with Pontificia Universidad Católica de Chile, is also making progress in the development of its optics and detectors. In addition to these, the development of a new optical instrument has been started this year. Allocation of the observing time was also determined. TAO will use approximately 45% of its scientific observation time as project time, 35% as Japan open time for the Japanese community, and 10% as Chilean time for the Chilean community. 5-15% will be provided as paid observing time.
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 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.
Since the University of Tokyo Atacama Observatory (TAO) is located in extremely high altitude (5,640 m.a.s.l.), safety management is one of the most important issues for the project. We have developed safety management program for work at the site in order to prevent medical illness for humans. In this program all staff have to take medical examinations such as Electrocardiogram and Hipobaria before their work starts. The results are reviewed by medical doctor. Only authorized staff can be permitted to work at the site. During stay in site, all staff need to always use oxygen supply because there is only half of the oxygen at the site. It is also important to understand physical workload at the site. Our safety staff reviews it and determines necessary resting time for each worker, e.g. great load works need to work 50 minutes and rest 10 minutes. In addition to low air pressure, very low temperature, extremely high UV radiation, and extremely dry atmosphere should be concerned. Our program requests all staff to use winter clothes, sunblock and UV protection sunglasses and a lot of potable water consumption. Keep communication is also very important to secure the safety. Normal telephone communication is not available as well as internet connectivity. We have established satellite communication as well as UHF internal communication for general works and safety coordination with other observatories in Atacama area.
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 Near-Infrared Cross-dispersed Echelle spectrograph (NICE) is a first light instrument for the TAO 6.5 m telescope. The instrument covers a wavelength range of 0.9 to 2.4 µm and has a resolving power of λ/∆λ ~2,600. NICE was first used on the 1.5 m infrared telescope at the National Astronomical Observatory of Japan from 2001 to 2005 and on the 1.6 m Pirka telescope in Japan from 2009 to 2018. We are now upgrading the cryogenics and computer system for the installation of NICE on the TAO telescope. Here we report on the current status and future schedules of instrumentation updates, control system, and modified specifications of NICE for its transfer to the TAO 6.5 m telescope.
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.
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.
One of remarkable features of the University of Tokyo Atacama Observatory (TAO) is an altitude of the site (5,640 m.a.s.l.) While this provides us an excellent condition for astronomical observations, the site development is attended with difficulty due to the hard conditions such as low pressure, low temperature, and limited access. Site preparation for the TAO 6.5 m telescope started in Apr. 2018. Firstly, we have constructed an access road from Pampa la bola plateau (~ 5,000 m.a.s.l) to the summit. It has a width of < 6.5 meter for transportation of telescope parts including the 6.5meter mirror. In order to prevent collapse, angle of side slope is carefully determined based on ground condition and frozen soils. All workers always use oxygen during their work as a measure against hypobaropathy. Since the site temperature in night is lower than 0 degree even in the summer season, it is difficult to ensure quality of foundation concrete if we cast it in-situ. We use pre-cast concrete for the foundation of the telescope, the enclosure, and the support building. The biggest part is the telescope foundation. It has a weight of 600 ton. Considering the transportation to the summit, it is divided into 43 parts and unified at the summit. This is a new trial to make a massive foundation for a large telescope with pre-cast concrete.
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.
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