National Astronomical Observatory of Japan (NAOJ) has had the responsibility for the Telescope Structure System (STR) of Thirty Meter Telescope (TMT) and engaged Mitsubishi Electric Corporation (MELCO) to take over the preliminary/final design and pre-production work since 2012. TMT defines that STR shall be designed to withstand earthquakes up to the levels of the 1000-years annual return period as keeping accelerations at the mirror/instrumental interface points below the specified thresholds. In this paper, we present the Seismic Isolation System (SIS) of TMT STR, as focusing on (1) the design to achieve compatibility of two conflicting performances that are the rigid connection to the ground during normal observations and flexible movement during seismic to suppress the seismic energy, (2) prototype results of the seismic isolation system, and (3) compliance status of the seismic requirements which is evaluated by time history analysis using the Finite Element Method (FEM) model of TMT STR.
How much light from the astronomical object actually reaches the focal plane of a telescope? To what extent the sensitivity can be extended to both ends of the visible wavelengths – ultraviolet (UV) and infrared (IR) – as much as possible from the ground? And how to maintain good throughput of the telescope optics? In this report, we make a simplified model to show effect in the reflectivity change of the telescope mirror from the recoating and cleaning versus degradation focusing on a segmented primary mirror of a telescope. The better understandings and monitoring of these competing factors will help fine tune the scheduling of the in-situ cleaning such as CO2 cleaning. By maintaining the high throughput of the optics, it becomes more feasible to catch rare atmospheric condition whenever it becomes available for very sensitive UV or IR observations during Moon’s dark and bright phases, respectively. The degradation not recoverable by the cleaning is reset by replacing dirty segments with freshly coated ones. The importance of regular in-situ cleaning is evident when it takes long time to replace the large number of freshly coated segments. It is important to clean the entire aperture as much as possible when a wet condition is forecast; for once the contamination settles on the surface, CO2 cleaning alone won’t be able to recover good surface characteristics of reflectivity, scattering, and emissivity.
The Thirty Meter Telescope (TMT) is expected to reveal the birth of galaxies, planetary surfaces and even the atmospheric composition of exoplanets. The TMT is an optical infrared reflecting telescope that uses very large hydrostatic bearings in the drive units. High precision is required for the sliding surface of the hydrostatic bearing. In the case of TMT, the radius of the hydrostatic bearing of the elevation journal is about 10 meters and it cannot be manufactured as an integral structure, so has a segmented structure. The size of each member of the segmented structure exceeds 10 meters. When high precision machining of about 30 micrometers is performed on the large structure exceeding 10 meters, it may take several days for a single process, which is greatly affected by changes in ambient temperature. Changes in ambient temperature not only cause thermal expansion and contraction of the workpiece, but also cause deformation of the machine tool. There are only a few large machine tools that can process parts over 10 meters in size. We constructed a temperaturecontrolled chamber that covers the large machine tool to prevent ambient temperature fluctuations. We compared the accuracy of machining in a room temperature (variable temperature) environment and machining in a constant temperature environment. This result demonstrates that machining errors can be suppressed in a constant temperature environment. In addition, this paper also shows the results of combining machining and the use of abrasive paper to finish the sliding surface, which improved the surface roughness without deforming the shape of the machined sliding surface. By using these improved machining methods, we were able to establish a precision machining method for large structures.
The Infrared Doppler (IRD) instrument is a fiber-fed high-resolution NIR spectrometer for the Subaru telescope covering the Y,J,H-bands simultaneously with a maximum spectral resolution of 70,000. The main purpose of IRD is a search for Earth-mass planets around nearby M-dwarfs by precise radial velocity measurements, as well as a spectroscopic characterization of exoplanet atmospheres. We report the current status of the instrument, which is undergoing commissioning at the Subaru Telescope, and the first light observation successfully done in August 2017. The general description of the instrument will be given including spectrometer optics, fiber injection system, cryogenic system, scrambler, and laser frequency comb. A large strategic survey mainly focused on late-type M-dwarfs is planned to start from 2019.
For the Thirty Meter Telescope (TMT) that aims high-resolution and high-sensitivity observations for optical-infrared astronomy, detailed design is underway for Telescope Structure System (STR) including the mount control system and the segment handling system. The technical requirements for the STR system are very challenging on its performance and interface condition with telescope-mounted optics and observation instruments. The major challenging technical requirements include low flexure of mirror support structure and low optical path length variation due to gravitational deformation, high seismic performance against large earthquake, very accurate mount drive control for high tracking and guiding performance, and fast, safe and labor-saving segment exchange. To meet these technical requirements, Mitsubishi Electric Corporation (MELCO) has made a detailed design and technology development. In this paper, overview of major key technologies is introduced that is adopted for the TMT telescope structure in the detailed design and technology development.
A future plan for the next-generation Subaru adaptive optics, is a system based on an adaptive secondary mirror. A ground-layer adaptive optics combined with a new wide-field multi-object infrared camera and spectrograph will be a main application of the adaptive secondary mirror. A preliminary simulation results show that the resolution achieved by the ground-layer adaptive optics is expected to be better than 0.2 arcsecond in the K-band over 15 arcminutes field-of-view. In this paper, the performance simulation is updated taking dependence on observation conditions, the zenith angle and the season, into account.
We present an overview of the design of IRIS, an infrared (0.84 - 2.4 micron) integral field spectrograph and imaging
camera for the Thirty Meter Telescope (TMT). With extremely low wavefront error (<30 nm) and on-board wavefront
sensors, IRIS will take advantage of the high angular resolution of the narrow field infrared adaptive optics system
(NFIRAOS) to dissect the sky at the diffraction limit of the 30-meter aperture. With a primary spectral resolution of
4000 and spatial sampling starting at 4 milliarcseconds, the instrument will create an unparalleled ability to explore high
redshift galaxies, the Galactic center, star forming regions and virtually any astrophysical object. This paper summarizes
the entire design and basic capabilities. Among the design innovations is the combination of lenslet and slicer integral
field units, new 4Kx4k detectors, extremely precise atmospheric dispersion correction, infrared wavefront sensors, and a
very large vacuum cryogenic system.
KEYWORDS: Telescopes, Optical instrument design, Computer aided design, Mirrors, Electroluminescence, Control systems design, Control systems, Earthquakes, Safety, Thirty Meter Telescope
We present an overview of the preliminary design of the Telescope Structure System (STR) of Thirty Meter Telescope (TMT). NAOJ was given responsibility for the TMT STR in early 2012 and engaged Mitsubishi Electric Corporation (MELCO) to take over the preliminary design work. MELCO performed a comprehensive preliminary design study in 2012 and 2013 and the design successfully passed its Preliminary Design Review (PDR) in November 2013 and April 2014. Design optimizations were pursued to better meet the design requirements and improvements were made in the designs of many of the telescope subsystems as follows: 1. 6-legged Top End configuration to support secondary mirror (M2) in order to reduce deformation of the Top End and to keep the same 4% blockage of the full aperture as the previous STR design. 2. “Double Lower Tube” of the elevation (EL) structure to reduce the required stroke of the primary mirror (M1) actuators to compensate the primary mirror cell (M1 Cell) deformation caused during the EL angle change in accordance with the requirements. 3. M1 Segment Handling System (SHS) to be able to make removing and installing 10 Mirror Segment Assemblies per day safely and with ease over M1 area where access of personnel is extremely difficult. This requires semi-automatic sequence operation and a robotic Segment Lifting Fixture (SLF) designed based on the Compliance Control System, developed for controlling industrial robots, with a mechanism to enable precise control within the six degrees of freedom of position control. 4. CO2 snow cleaning system to clean M1 every few weeks that is similar to the mechanical system that has been used at Subaru Telescope. 5. Seismic isolation and restraint systems with respect to safety; the maximum acceleration allowed for M1, M2, tertiary mirror (M3), LGSF, and science instruments in 1,000 year return period earthquakes are defined in the requirements. The Seismic requirements apply to any EL angle, regardless of the operational status of Hydro Static Bearing (HSB) system and stow lock pins. In order to find a practical solution, design optimization study for seismic risk mitigation was carried out extensively, including the performing of dynamic response analyses of the STR system under the time dependent acceleration profile of seven major earthquakes. The work is now moving to the final design phase from April 2014 for two years.
We report the current status of the Infrared Doppler (IRD) instrument for the Subaru telescope, which aims at detecting
Earth-like planets around nearby M darwfs via the radial velocity (RV) measurements. IRD is a fiber-fed, near infrared
spectrometer which enables us to obtain high-resolution spectrum (R~70000) from 0.97 to 1.75 μm. We have been
developing new technologies to achieve 1m/s RV measurement precision, including an original laser frequency comb as
an extremely stable wavelength standard in the near infrared. To achieve ultimate thermal stability, very low thermal
expansion ceramic is used for most of the optical components including the optical bench.
Hyper Suprime-Cam (HSC) is an 870 Mega pixel prime focus camera for the 8.2 m Subaru telescope. The wide field corrector delivers sharp image of 0.25 arc-sec FWHM in r-band over the entire 1.5 degree (in diameter) field of view. The collimation of the camera with respect to the optical axis of the primary mirror is realized by hexapod actuators whose mechanical accuracy is few microns. As a result, we expect to have seeing limited image most of the time. Expected median seeing is 0.67 arc-sec FWHM in i-band. The sensor is a p-ch fully depleted CCD of 200 micron thickness (2048 x 4096 15 μm square pixel) and we employ 116 of them to pave the 50 cm focal plane. Minimum interval between exposures is roughly 30 seconds including reading out arrays, transferring data to the control computer and saving them to the hard drive. HSC uniquely features the combination of large primary mirror, wide field of view, sharp image and high sensitivity especially in red. This enables accurate shape measurement of faint galaxies which is critical for planned weak lensing survey to probe the nature of dark energy. The system is being assembled now and will see the first light in August 2012.
M. Tamura, H. Suto, J. Nishikawa, T. Kotani, B. Sato, W. Aoki, T. Usuda, T. Kurokawa, K. Kashiwagi, S. Nishiyama, Y. Ikeda, D. Hall, K. Hodapp, J. Hashimoto, J. Morino, S. Inoue, Y. Mizuno, Y. Washizaki, Y. Tanaka, S. Suzuki, J. Kwon, T. Suenaga, D. Oh, N. Narita, E. Kokubo, Y. Hayano, H. Izumiura, E. Kambe, T. Kudo, N. Kusakabe, M. Ikoma, Ya. Hori, M. Omiya, H. Genda, A. Fukui, Y. Fujii, O. Guyon, H. Harakawa, M. Hayashi, M. Hidai, T. Hirano, M. Kuzuhara, M. Machida, T. Matsuo, T. Nagata, H. Ohnuki, M. Ogihara, S. Oshino, R. Suzuki, H. Takami, N. Takato, Y. Takahashi, C. Tachinami, H. Terada
IRD is the near-infrared high-precision radial velocity instrument for the Subaru 8.2-m telescope. It is a relatively compact (~1m size) spectrometer with a new echelle-grating and Volume-Phase Holographic gratings covering 1-2 micron wavelengths combined with an original frequency comb using optical pulse synthesizer. The spectrometer will employ a 4096x4096-pixel HgCdTe array under testing at IfA, University of Hawaii. Both the telescope/Adaptive Optics and comb beams are fed to the spectrometer via optical fibers, while the instrument is placed at the Nasmyth platform of the Subaru telescope. Expected accuracy of the Doppler-shifted velocity measurements is about 1 m s-1. Helped with the large collecting area and high image quality of the Subaru telescope, IRD can conduct systematic radial velocity surveys of nearby middle-to-late M stars aiming for down to one Earth-mass planet. Systematic observational and theoretical studies of M stars and their planets for the IRD science are also ongoing. We will report the design and preliminary development progresses of the whole and each component of IRD.
A wide-field adaptive optics system based on an adaptive secondary mirror (ASM) is one of a future plan for
the next-generation Subaru adaptive optics system. The main application of ASM based AO will be a groundlayer
adaptive optics (GLAO) with field-of-view larger than 10 arc minutes. The high Strehl-ratio of on-source correction by high-order ASM (expected to be about 1000) and the reduction of emissivity are also attractive points. In this paper, we report a preliminary result of simulations for the these applications of ASM to study conceptual design of the next-generation wide-field Subaru adaptive optics.
We describe an optical design of an imager mode of the IRIS instrument for the Thirty Meter Telescope. IRIS
is a fully-cryogenic diffraction-limited infrared camera and integral field spectrograph working in the wavelength
coverage from 0.84 to 2.4 microns. The imager mode covers 16.4" × 16.4" FOV with a 4096 × 4096 detector
array with sampling 4 milli-arcsec/pix. There are two challenges in performance which the science cases require
in the imager mode. 1) rms wavefront error should be less than 30 nm, and 2) optical distortion should be
corrected sufficiently to achieve astrometric accuracy of 10 micro-arcsec. Among possible optical configurations
consisting of reflective and refractive solutions, a refractive solution with apochromatic triplets best meets the
requirements. The optical system consists of a collimator and camera both of which have a BaF2-Fused Silica-
ZnSe apochromatic triplet and a single BaF2 lens near the focus. The rms wavefront error of the system including
the telescope, adaptive optics, and imager mode is less than 22 nm with ideal optical parameters. A sensitivity
analysis shows that reasonable amount of errors in fabrication and alignment will give the rms wavefront error of
less than 30 nm in 90 % of all cases. We also investigate accuracy of the distortion correction and how movable
parts affect the correction accuracy. We find that uncorrectable distortion correction errors are well below 10
micro-arcsec with reasonable stability and repeatability of the movable parts.
We present an overview of the design of IRIS, an infrared (0.85 - 2.5 micron) integral field spectrograph and imaging
camera for the Thirty Meter Telescope (TMT). With extremely low wavefront error (<30 nm) and on-board wavefront
sensors, IRIS will take advantage of the high angular resolution of the narrow field infrared adaptive optics system
(NFIRAOS) to dissect the sky at the diffraction limit of the 30-meter aperture. With a primary spectral resolution of
4000 and spatial sampling starting at 4 milliarcseconds, the instrument will create an unparalleled ability to explore high
redshift galaxies, the Galactic center, star forming regions and virtually any astrophysical object. This paper summarizes
the entire design and basic capabilities. Among the design innovations is the combination of lenslet and slicer integral
field units, new 4Kx4k detectors, extremely precise atmospheric dispersion correction, infrared wavefront sensors, and a
very large vacuum cryogenic system.
Developing new instruments and upgrading existing instruments has been an important aspect of Subaru telescope's
operation. Seven facility instruments and two visiting instruments are currently under use. Among them
HiCIAO, a coronagraphic imager combined with adaptive optics (AO188), has started its full operation in the 2nd
semester of 2009. We are using HiCIAO for a large program (SEEDS) to find new exo-planets and comprehend
planet formation from proto-planetary disks. To achieve higher contrast, a new coronagraph attachment with an
extreme AO (SCExAO) will be installed as a PI instrument. AO188 is also used with the IRCS in natural guide
star mode. Its laser guide star mode is currently commissioning. The Fibre multi-object spectrograph (FMOS),
which is comprised of 400 fibers placed at the prime focus and delivers 0.9-1.8um spectra, will be partly offered
to open use from mid 2010. Hyper Suprime-Cam, the wide-field upgrade (1.5 deg FoV) of the Suprime-Cam, is
under development for its first light in 2011. Development of an immersion grating has taken place for upgrading
the IRCS with a high-resolution infrared spectrograph.
In the context of instrumentation for Extremely Large Telescopes (ELTs), an Integral Field Spectrographs
(IFSs), fed with a Multi-Object Adaptive Optics (MOAO) system, has many scientific and technical advantages.
Integrated with an ELT, a MOAO system will allow the simultaneous observation of up to 20 targets in a several
arc-minute field-of-view, each target being viewed with unprecedented sensitivity and resolution. However,
before building a MOAO instrument for an ELT, several critical issues, such as open-loop control and calibration,
must be solved. The Adaptive Optics Laboratory of the University of Victoria, in collaboration with the Herzberg
Institute of Astrophysics, the Subaru telescope and two industrial partners, is starting the construction of a
MOAO pathfinder, called Raven. The goal of Raven is two-fold: first, Raven has to demonstrate that MOAO
technical challenges can be solved and implemented reliably for routine on-sky observations. Secondly, Raven
must demonstrate that reliable science can be delivered with multiplexed AO systems. In order to achieve these
goals, the Raven science channels will be coupled to the Subaru's spectrograph (IRCS) on the infrared Nasmyth
platform. This paper will present the status of the project, including the conceptual instrument design and a
discussion of the science program.
The High-Contrast Coronographic Imager for Adaptive Optics (HiCIAO), is a coronographic simultaneous differential
imager for the new 188-actuator AO system at the Subaru Telescope Nasmyth focus. It is designed primarily to search
for faint companions, brown dwarves and young giant planets around nearby stars, but will also allow observations of
disks around young stars and of emission line regions near other bright central sources. HiCIAO will work in
conjunction with the new Subaru Telescope 188-actuator adaptive optics system. It is designed as a flexible,
experimental instrument that will grow from the initial, simple coronographic system into more complex, innovative
optics as these technologies become available. The main component of HiCIAO is an infrared camera optimized for
spectral simultaneous differential imaging that uses a Teledyne 2.5 μm HAWAII-2RG detector array operated by a
Sidecar ASIC. This paper reports on the assembly, testing, and "first light" observations at the Subaru Telescope.
We present an upgrade plan of the infrared camera and spectrograph for the Subaru Telescope (IRCS1-4) to introduce the high resolution spectroscopic mode (a resolving power; R=λ/Δλ > 70,000) in the infrared bands
(1.4-5.5 μm). To realize the compact and stable cooled instrument, we are developing the immersion grating5 with Si whose refractive index is ~ 3.4. The optics design is significantly compact (600mm × 250mm × 250mm) using the Si immersion grating, and it can be easily located beside or inside the IRCS main dewar. The IRCS
has been operating for 8 years with an extremely stable condition, and it is combined with the next generation adaptive optics system (AO1886) and the laser guide star system (LGS7) of the Subaru Telescope. The quick integration of the new high resolution spectrograph unit (HRU) can be expected by using the existing stable
instrument. The total performance with the designed optics is so good that the optical design could meet the required specifications. The image quality shows a strehl ratio of > 0.88 for the entire bands, and 24 scannings of the gratings can cover the 1.4-5.5 μm. We plan to fabricate the Si immersion grating for the actual astronomical
use in 2009, and the HRU will be built around 2011. It will be the first high sensitive infrared spectrograph with high spectral resolution capability in the northern hemisphere and with the laser guide star AO system.
The Subaru Telescope has been operated smoothly for eight years after its first light. With the advent of instruments with high spatial resolution such as the adaptive optics, elongation of images has been noticed towards specific azimuth (AZ) and elevation (EL). With accelerometers with high time resolution, we detected vibrations of the telescope and could attribute the elongation of images to the vibrations. The detected vibrations are at 3.6 Hz and at 7-9 Hz in AZ direction and at 5-6 Hz in EL direction. Image motion due to these vibrations is 0.4 arcsec peak-to-peak at maximum, which is not negligible compared to image motion of 0.063 arcsec rms in quiescent state. The motion, which can not be canceled with the auto guider, results in elongation of images. The 3.6 Hz vibration in AZ direction is only excited while culmination EL of above 80 degrees. The 7-9 Hz vibration in AZ direction and the 5-6 Hz vibration in EL direction are excited by periodic errors in incremental encoders which are used to measure velocity of telescope rotation. We investigated possibilities to reduce the vibrations with tuning control loops of the AZ and EL axes.
The 8 m SUBARU telescope atop Mauna Kea on Hawaii will shortly be equipped with a 188 actuator adaptive optics system (AO 188). Additionally it will be equipped with a Laser guide star (LGS) system to increase the sky coverage of that system. One of the additional tip-tilt sensor which is required to operate AO 188 in LGS mode will be working in the infrared to further enhance the coverage in highly obscured regions of the sky. Currently, various options for this sensor are under study, however the baseline design is a pyramid wavefront sensor. It is currently planned to have this sensor be able to provide also information on higher modes in order to feed AO 188 alone, i.e. without the LGS when NIR-bright guide stars are available. In this paper, we will present the results of the basic design tradeoffs, the performance analysis, and the project plan. Choices to be made concern the number of subapertures available across the primary mirror, the number of corrected modes, control of the AO system in combination with and without LGS, the detector of the wavefront sensor, the operation wavelength range and so forth. We will also present initial simulation results on the expected performance of the device, and the overall timeline and project structure.
The Subaru telescope had its astronomical first light in January 1999 and has been stably operated since the common use started in December 2000. The telescope is mounted on an alt-azimuth structure. The structure of 550 tons is supported by six hydrostatic oil pads which lift the structure by 50 microns. The azimuth (Az) and elevation (El) axes are driven by direct-drive linear motors, ensuring very smooth pointing and tracking operations. The Az rail consists of eight circular arc pieces. They were installed in January 1997 with a peak-to-peak level of within 0.1mm. However at a later time, vertical undulations of the Az rail were found to be more than 0.2 mm peak-to-peak at some locations where the telescope structure in the rest position applies load. Open-loop tracking accuracy of the telescope, which was about 2 arcsec RMS on the sky, was found to be due to the undulations of the Az rail. We made a table to correct telescope pointings due to the undulations. It has made open-loop tracking accuracy better than 0.2arcsec RMS. Since then, we have been monitoring the flatness of the Az rail. So far the undulations have not changed.
To get the strategy to confirm image qualities of Subaru Telescope, we have obtained the statistics of seeing measured with auto guider images obtained during scientific observations. In addition to this, we started a regular operation of a stationary DIMM at the Subaru Telescope site. From the data of natural seeing measured with the DIMM, we expect to reveal contributions of telescope vibration, inadequate enclosure ventilation, or optical aberrations including deformation of primary mirror by wind load. The stationary DIMM station consists of one 30 cm diameter DIMM, its enclosure, the local control unit and Linux based control PC. We put our DIMM station at the catwalk of the Subaru enclosure at the level of 12-m from the ground, because the high location from the ground can minimize the influence of ground layer. We describe details of our DIMM station and show seeing data obtained since June 2005 and comparison with the seeing obtained with Subaru auto guider images in order to check whether the enclosure of Subaru Telescope may affect the DIMM to measure the seeing.
We have a plan to install a micro-crack alert system for the primary
mirror of Subaru Telescope based on the monitoring of the acoustic
emission from any incident events. We report the results of our preliminary experiment for characterizing the acoustic properties of actual Subaru primary mirror. The attenuation of acoustic wave was confirmed to be small enough to allow detection of such events at any locations of the mirror. The position of incident events that might lead to the generation of possible micro-cracks can be identified within less than 3 cm accuracy by placing seven acoustic sensors along the circumference of the primary mirror.
The Subaru Telescope has been stably operated with high image quality since common use began in December 2000. We have updated the following items in order to achieve further improvement of observation efficiency, image quality, and tracking. 1. High reflectivity of mirrors. The reflectivity of the primary mirror has been maintained, yielding 84% at 670 nm by regular CO2 cleaning (every two to three weeks). We successfully carried out the silver coating of the Infrared secondary mirror in April 2003 without over-coating. The reflectivity has been maintained at greater 98% at 1,300 nm. 2. Image Quality. Subaru telescope delivers exceptional image quality {a median image size of 0.6 arc-second FWHM in the R-band as taken by Auto-Guider Cameras at all four foci; Prime, Cassegrain, and two Nasmyth. We optimized parameters of the servo control system of the Elevation servo, reducing the amplitude of 3{8 Hz vibration mode of the telescope and improving image quality when using the Adaptive Optics (AO) system. 3. Acquisition Guiding. Dithering time was shortened by updating the control software. The slit viewer camera for HDS and the fiber bundle for FMOS are available for acquisition guiding in addition to Auto-Guider Cameras. 4. New instruments. We are developing a new prime focus unit for FMOS and will start functional tests in 2005. Moreover, we have started to prepare new interfaces and facilities for FMOS and the new 188 element AO natural/laser guide star system. The focus switching time
will be shortened by updating the hardware of the IR and Cassegrain Optical secondary mirrors from September 2004, reducing it to 10 minutes to switch the focus between Cassegrain and Nasmyth foci.
We have been taking weather data at the location of the Subaru Telescope since 1999. We have also obtained the environmental data on many points in the telescope enclosure and on the telescope structure. Based on those, we will report the statistics of weather data and environmental condition around the Subaru Telescope as well as correlations among them. The statistics of nighttime clear sky ratios at Subaru Telescope site is presented. We have been gathering seeing data since the First Light of the Subaru Telescope in 1999, and we found a clear seasonal variation of the seeing size defined by FWHM method. A strong correlation between seeing sizes and wind velocities/directions is reported.
The SUBARU Telescope has four focal positions to allow different types of astronomical instrument. At present, there are four different Top Units; three types of secondary mirrors and one primary focus unit. IR secondary mirror which is one of the three units, has silver coated surface. Other secondary mirrors are coated by aluminum for observations at visible wavelength. The silver coating for IR secondary mirror was first carried out in 1999 at the medium size (1.6 m) vacuum evaporation chamber in Mitaka campus of NAOJ at Tokyo JAPAN. Since then the reflectivity had deteriorated over the years. Then, we made a plan to recoat IR secondary mirror in 2003 using the SUBARU’s large-size vacuum evaporation chamber at the summit facility on Mauna Kea, Hawaii. Some tests were performed for silver vacuum evaporation at the base facility, and then the IR secondary mirror was recoated at the summit. The reflectivity achieves 97.6% and 99.3% at the wavelength of 500 nm and 2000 nm, respectively. Degradation of the coat has not been seen 8 months after recoating. We also performed the recoating of the aluminum surface of the primary mirror in 2003. This year we made effort to simplify the procedure. The reflectivity is 91.2% and 97.4% at the wavelength of 500 nm and 2000 nm, respectively.
Subaru Telescope has currently achieved the following performances. 1. Image Quality. (1) Subaru Telescope delivers a median image size, evaluated by equipped Auto Guider (AG) cameras, of 0.6-0.7 arcsec FWHM in the R and I-band at all the four foci: Prime (P), Cassegrain (Cs), and tow Nasmyth (Ns). (2) The best image sizes obtained so far are 0.2 arcsecs FWHM without AO in near-infrared (IR), less than 0.1 arcsec FWHM with AO, and 0.3 arcsec FWHM in optical and mid-IR wavelengths. (3) Stable Shack-Hartmann measurement enables one to keep the errors of Zernike coefficients to less than 0.2μm which corresponds to ~0.1 arcsec image size. 2. Tracking and Pointing. (1) Blind pointing accuracy is better than 1 arcsec RMS over most of the sky. (2) Tracking accuracy is better than 0.2 arcsec RMS in 10 minutes. (3) Guiding accuracy is between 0.8 and 0.18 arcsec RMS with 12-18th magnitude guide stars. 3. IR secondary mirror (M2). (1) Chopping performances: typical figures are at 3 Hz, 80% duty cycle with 30-60 arcsec chopping throw. (2) Tip-Tilt performances: Position stability is about 0.030 arcsec RMS for the effective closed-loop bandwidth less than 5 Hz. 4. Others. (1) The reflectivity of the primary mirror has been maintained at higher than 85 and 95% at 670 and 1300 nm wavelengths by regular cleaning with CO2 ice every two to three weeks. (2) The reflectivity of the blue-side image rotator (ImR) at Nasmyth-optical focus was improved after re-coating of mirrors.
We report current status of active mirror support of Subaru telescope. Total wavefront error we provide for observation is 150-300 nm rms . Elevation dependency of the shape of the primary mirror and wind buffeting effect are shown. We also show a procedure for SH measurements at prime focus with half-cut (D-shape) pick-up mirror.
KEYWORDS: Control systems, Telescopes, Infrared telescopes, Local area networks, LabVIEW, Infrared radiation, Signal processing, Astronomical telescopes, Astronomy, Observatories
We report on the status of the Cassegrain Instrument Automatic Exchanger (CIAX) control system for the Subaru Telescope. Devices controlled by a shell program in the previous version are now controlled by a macro. It can now be operated safely from remote site. Features of the new system are: 1. New macro. The new macro has two features: (1) Action skip. The macro can skip actions that have been executed earlier. It judges whether to skip by checking the status of devices. Resumption of interrupted macro or reversal from halfway of a process is possible. (2) Macro flexibility: The script has every possible sequential action and chooses actions by checking device status. For instance, it can determine whether the cart is at the telescope or at one of the instrument standby flanges and select a proper hookup command. 2. GUI for macro operation and CGI for rewriting setup files. The new GUI uses a commercial instrument control language. A CGI application accesses setup files. 3. Omni-directional Infrared (IR) LAN. Omni-directional IR LAN is being tested for the cart because radio frequency wireless LAN is prohibited on Mauna Kea to avoid interference to radio telescopes. Conventional IR LAN failed because of its directionality. The CIAX system is now routinely used for instrument exchange. For complete automatic operation, there are still a few tasks left, such as macro-controlled instrument shutdown and restarting, standardizing interfaces and procedure for all instruments and further increasing reliability which is higher already compared to conventional manual exchange.
The CIAX system especially CIAX-3 increased observation efficiency for Cassegrain test instruments at the early phase of Subaru telescope test observation. In order to control this system effectively and automatically, a control software for the entire system of the CIAX was developed. The software design goals are (1) redundancy for robust system, (2) the safety of the instrument by interlocking, (3) maximum efficiency by automatic control and (4) easy user interface for operator. In this paper, we describe the software which has been being tested through the telescope and instrument commissioning phase.
The Cassegrain Instrument Automatic eXchanger (CIAX) system for the 8.2 meter Subaru Telescope moves instruments between the Cassegrain mounting flange and stand-by flanges without manual intervention. Observation efficiency improves not only because of quick exchanges, scheduled or emergency, but also because of increased flexibility in selecting an optimum instrument for weather conditions or observation goals. Reliable and safer instrument exchanges are achieved by the precision mechanical positioning system (less than 0.5 mm) and an automatic connector system for electrical cables, optical fibers and fluid lines. Instrument down time due to connector/cable failure by human error is eliminated. Interfaces to the telescope flange are standardized for all five Cassegrain instruments (approximately 2000 kgf each) currently in use or under preparation.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.