We have prepared remote observing environment for the 188 cm telescope at Okayama Astrophysical Observatory. A KVM-over-IP and a VPN gateway are employed as core devices, which offer reliable, secure and fast link between on site and remote sites. We have confirmed the KVM-over-IP has ideal characteristics for serving the remote observing environment; the use is simple for both users and maintainer; access from any platform is available; multiple and simultaneous access is possible; and maintenance load is small. We also demonstrated that the degradation of observing efficiency specific to the remote observing is negligibly small. The remote observing environment has fully opened since the semester 2016A, about 30% of the total observing time in the last semester was occupied by remote observing.
Two types of field measurements on the Atacama Submillimeter Telescope Experiment 10-m antenna have been made to
diagnose antenna oscillations in strong wind gusts and to reduce pointing errors due to static/quasi-static wind loadings.
The measurements with seismic accelerometers on the reflector have been compared with those from axis angle encoders.
Our results have confirmed that the dominant wind effects are at low frequencies, and have found that twist and pitching
motion of yoke arms are the dominant source of pointing jitters and decrease with frequency along the Kolmogorov
slope of -5/3. In the range from about 1 to 10 Hz, the servo-loop excites and dominates pointing error oscillations. For
azimuth oscillations, the frontal wind has the largest effects, compared with side- or tail-wind. To improve pointing
performance against static/quasi-static wind effects, we have implemented and tested an auxiliary auto-pointingcorrection
system with a lookup table compiled from all-sky pointing measurements under strong winds, invoking the
Taylor's "frozen turbulence" hypothesis. We have successfully demonstrated that use of upwind data from a nearby
anemometer helps to reduce the pointing errors of static wind effects from 2.4 " rms (correction OFF) to 1.2 " rms
(correction ON) under a mean wind speed of 9.3 m s-1.
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.
Reflector surface deformation due to wind loading on the Nobeyama
45-m antenna has been measured with four LED
lamps on the surface at r = 20 m and two CCD cameras on the central hub as it rotates in azimuth with elevation angles
of 90 and 11 degrees. The side-wind loading of 8.4 m s-1 caused a tilt of 12 arcseconds and an astigmatic deformation of
0.8 mm. The front- and back-wind loading of 9.9 m s-1 induced a vertical displacement variation of 2.3 mm. These largescale
surface deformation profiles have been compared with those of finite element calculations and coefficients of axial
force and yaw moment predicted by a JPL wind tunnel data excerpt.
Direct exploration of exoplanets is one of the most exciting topics in astronomy. Our current efforts in this field are concentrated on the Subaru 8.2m telescope at Mauna Kea, Hawaii. Making use of the good observing site and the excellent image quality, the infrared coronagraph CIAO (Coronagraphic Imager with Adaptive Optics) has been used for various kinds of surveys, which is the first dedicated cold coronagraph on the 8-10m class telescopes. However, its contrast is limited by the low-order adaptive optics and a limited suppression of the halo speckle noise.
HiCIAO is a new high-contrast instrument for the Subaru telescope. HiCIAO will be used in conjunction with the new adaptive optics system (188 actuators and/or its laser guide star - AO188/LGSAO188) at the Subaru infrared Nasmyth platform. It is designed as a flexible camera comprising several modules that can be configured into different modes of operation. The main modules are the AO module with its future extreme AO capability, the warm coronagraph module, and the cold infrared camera module. HiCIAO can combine coronagraphic techniques with either polarization or spectral simultaneous differential imaging modes. The basic concept of such differential imaging is to split up the image into two or more images, and then use either different planes of polarization or different spectral filter band-passes to produce a signal that distinguishes faint objects near a bright central object from scattered halo or residual speckles.
In this contribution, we will outline the HiCIAO instrument, its science, and performance simulations. The optical and mechanical details are described by Hodapp et al. (2006)1. We also present a roadmap of Japanese facilities and future plans, including ASTRO-F (AKARI), SPICA, and JTPF, for extrasolar planet explorations.
Periodic vortex shedding from a 12-m parabola antenna has been found in the wind of 9 m s-1 and an attack angle of 26
degrees. The measurements have been made at the NRAO VLA site. The periodic yaw motion of an elevation axis has
been detected with linear gauges mounted on a reference structure that was built in each side of the yoke. It has also been
observed in the angle difference of two encoders installed at both ends of the elevation axis. The frequency of yaw
motion was 0.15 Hz. The same periodicities have been found in both the wind direction and wind velocity measured with
an ultrasonic anemometer in the wake downstream of the antenna. Such periodicities have been seen in neither common
displacement of the bearing housings nor rotation of the elevation axis. The Reynolds number of the flow was 6 x 106
(hypercritical), suggesting the vortex shedding be periodic, which is consistent with our observations. The Strouhal
number of parabola has been found to be 0.19 that is comparable to those of cylinder, inverse triangle, and other similar
geometric shapes. The coefficient for oscillatory lateral force exerted on the antenna by shedding vortices has been
estimated to be about 1.
The National Astronomical Observatory of Japan has constructed a prototype 12-m antenna of the Atacama Compact Array to evaluate its performance at the ALMA Test Facility in the NRAO VLA observatory in New Mexico, the United States. The antenna has a CFRP tube backup structure (BUS) with CFRP boards to support 205 machined Aluminum
surface panels. Their accuracies were measured to be 5.9 m rms on average. A chemical treatment technique of the surface panels has successfully applied to scatter the solar radiation, which resulted in a subreflector temperature increase of about 25 degrees relative to ambient temperature during direct solar observations. Holography measurements and panel adjustments led to a final surface accuracy of 20 m rms, (weighted by 12dB edge taper), after three rounds of the panel adjustments. Based on a long term temperature monitoring of the BUS and thermal deformation FEM calculation, the BUS thermal deformation was estimated to be less than 3.1 m rms. We have employed gear drive mechanism both for a fast position switching capability and for smooth drive at low velocities. Servo errors measured with angle encoders were found to be less than 0.1 arcseconds rms at rotational velocities below 0.1 degrees s-1 and to increase to 0.7 arcseconds rms at the maximum speed of the 'on-the-fly' scan as a single dish, 0.5 deg s-1 induced by the irregularity of individual gear tooth profiles. Simultaneous measurements of the
antenna motion with the angle encoders and seismic accelerometers mounted at the primary reflector mirror edges and at the subreflector showed the same amplitude and phase of oscillation, indicating that they are rigid, suggesting that it is possible to estimate where the antenna is actually pointing from the encoder readout. Continuous tracking measurements of Polaris during day and night have revealed a large pointing drift due to thermal distortion of the yoke structure. We have applied retrospective thermal corrections to tracking data for two hours, with a preliminary thermal deformation model of the yoke, and have found the tracking accuracy improved to be 0.1 - 0.3 arcseconds rms for a 15-munites period. The whole sky absolute pointing error under no wind and during night was measured to be 1.17 arcseconds rms. We need to make both an elaborated modeling of thermal deformation of the structure and systematic searches for
significant correlation among pointing errors and metrology sensor outputs to achieve the stable tracking performance requested by ALMA.
Next generation radio telescope designs face two serious technical challenges in pointing accuracy. The first is that improved resolution requires more precise pointing, and the second is that increased size makes that pointing accuracy even harder to achieve. New telescopes, such as the 50 m LMT/GTM, require sub-arcsecond pointing in significant wind, whereas current large radio telescopes point only to a couple of arcseconds without wind. A commonly proposed solution to the pointing problem is laser metrology. In this approach, structural deformations are measured, enabling correction of the resulting pointing errors. These measurements are typically slow, allowing only quasi-static effects to be removed. However, the low natural frequencies of large structures allow a significant response to the frequency content of the wind. This effect is difficult to calculate accurately because of both the limited knowledge of the actual wind power spectrum and the complex interaction of the wind with the structure. To investigate the dynamic behavior of large radio telescope in the wind, we conducted pointing measurements with the Nobeyama Radio Observatory (NRO) 45 m telescope. We measured the pointing error in elevation and cross-elevation as a function of time and wind speed, and examined the frequency content of the results. We present results which confirm that the dominant wind effects are at low frequencies, suitable for elimination via a laser-based system. However, the resonant behavior of the telescope is clearly visible in the data, and these dynamic errors are the dominant effects above about 0.1 Hz, even in modest (approximately 4 m/s) wind. As a result, an understanding of this dynamic behavior will be essential for the design of future large telescopes and metrology systems.
A large focal plane array receiver system for the NRO 45 m telescope (SIS 25-BEam Array Receiver System, or BEARS) is described. This new array receiver uses SIS junctions and has 25 elements. It can operate at the frequency range of 82 - 116 GHz. The development of this new system is almost complete. We describe about the whole system in detail, which includes the receiver, the IF systems, the new spectrometers and the remote control systems. We also describe about the performances and the uniformity of the system and show the astronomical result.
We are developing high quality reflector panels for the new 10-m telescope for millimeter/sub-millimeter waves, which is to be a prototype antenna for LMSA/ALMA. The telescope consists of 205 reflector panels, and is expected to achieve the surface accuracy of 17 micrometer for the entire telescope. Each reflector panels are machined from a single block of aluminum in size of 80 cm X 80 cm and weighs 15 kg/m2. The panel surface needs to be processed not to focus the sun-light on to the sub-reflector and the support structure to protect them from heating up. We have examined several methods for surface processing, including scratching the surface by a steel-wool or a sandpaper, and to blast sand like small particles against the panel surface. As a result, we found the sand-blast process to be the acceptable solution. The scattering width for the sun-lights were measured to be 86 degree(s) (FWHM), which feeds less than 1% of the incident sun- light to the sub-reflector, and causes temperature increase of only 45 degree(s)C. The sub-millimeter reflectivity of the sand- blasted panel was measured with the Fourier transform spectrometer which showed that the sand-blast process does not affect the reflectivity for the sub-millimeter waves up to 1.5 THz. The reflector panel mounted on the telescope is yet to be processed for scattering the sun-light in the near future.
A 10-m submillimeter telescope designed for interferometric observations at bands from 3 to 0.3 mm has constructed at Nobeyama Radio Observatory. The telescope is an engineering model for a large millimeter and sub-millimeter array, and will be operated for developments of sub-millimeter observation techniques at a remote site. We have fabricated lightweight machined aluminum panels (15 kg m-2) that have a surface accuracy of 5 micrometer rms. They have a typical size of 0.8 m X 0.6 m, and are supported with three motorized screws. The back-up structure is constructed of a central hub of low thermal expansion alloy, and CFRP honeycomb boards and tubes. Holography measurements will be made with a nearby transmitter at 3 mm. The overall surface accuracy is expected to be < 25 micrometer rms; the goal being 17 micrometer rms. We have achieved an accuracy of 0.03' rms for angle encoders. The drive and control system is designed to achieve a pointing error of 1'.0 rms with no wind and at night. Under a wind velocity of 7 m s-1, the pointing error increases to 2'.0 rms. An optical telescope of 10-cm diameter mounted on the center hub will be used to characterize pointing and tracking accuracy. Thermal effects on the pointing and surface accuracy will be investigated using temperature measurements and FEM analyses. The fast position switching capability is also demanded to cancel atmospheric fluctuations. The antenna is able to drive both axes at a maximum velocity of 3 deg s-2 with a maximum acceleration of 6 deg. s-2. The telescope is currently equipped with SIS receivers for 100, 150, 230, and 345 GHz and a continuum backend and an FX-type digital autocorrelator with an instantaneous bandwidth of 512 MHz and 1024 channel outputs.