Akihiko Miyashita

Current performance and on-going improvements of the 8.2 m Subaru Telescope

An overview of the current status of the 8.2m Subaru Telescope constructed and operated at Mauna Kea, Hawaii, by the National Astronomical Observatory of Japan is presented. The basic design concept and the verified performance of the telescope system are described. Also given are the status of the instrument package offered to the astronomical community, the status of operation, and some of the future plans. The status of the telescope reported in a number of SPIE papers as of the summer of 2002 are incorporated with some updates included as of 2004 February. However, readers are encouraged to check the most updated status of the telescope through the home page, http://subarutelescope.org/index.html, and/or the direct contact with the observatory staff.

Subaru Telescope: current performances and future upgrade plans

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.

Temperature control for the primary mirror and seeing statistics of Subaru Telescope

Based on the successful numerical weather forecasting performed by collaboration between MKWC and Subaru Telescope, we develop a temperature control system of the primary mirror of the Subaru Telescope. Temperature forecast is accurate 80% in 2 degrees. After to start the operation, the temperature of the primary mirror controlled below 1 degree centigrade compare by the ambient night air temperature in over 70% probability. The effect of the temperature control for the improvement of the seeing of Subaru telescope seems to be moderately effective.The median of the seeing size of Subaru Telescope on May 2000 to July 2002 is 0.69 arcsec FWHM. We need further investigation whether the improvement is the result of our successful temperature control system of the primary mirror, or the effect of the annual variation of seeing itself. Thus, we need a long period data for verification the effect of the temperature control.

Statistics of the weather data, environment data, and the seeing of the Subaru Telescope

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.

All-sky 10 μm cloud monitor on Mauna Kea

We report an infrared all sky cloud monitor operating at Subaru telescope at Mauna Kea, Hawaii. It consists of panoramic optics and a 10 μm infrared imager. Aspheric metal mirrors coated with gold (sapphire over-coated) are used in the panoramic optics, which is similar to the MAGNUM observatorys cloud monitor at Haleakala, Maui. The imager is a commercially available non-cooled bolometer array. The system is waterproof and (almost) maintenance-free. The video signals from the imager are captured, averaged over 50 frames, subtracted clear-sky frame and flat-fielded in two minutes interval. The processed cloud images are transferred to Subaru observational software system (SOSS) and displayed combined with telescope/targets information and also stored to Subaru Telescope data archive system (STARS). The processed images will be opened on Internet web site.

Development of zodiacal light observation system: WIZARD

We describe a new system (WIZARD: Wide-field Imager of Zodiacal light with ARray Detector) for the zodiacal light observation developed by a Korean and Japanese zodiacal light observation group. Since the zodiacal light is faint and wide-spread all over the sky, it consists of a very sensitive CCD camera of a quantum efficiency of 90% at 460(nm) and a wide angle lens with the field-of-view of 49x98 (degree). WIZARD is designed to measure the absolute brightness of diffuse sky in visible wavelengths. The zodiacal component will be separated from the integrated starlight, the airglow continuum and the scattered light in the atmosphere in the data reduction procedure. We got a first image by WIZARD in 2001 at Mauna Kea (4200m, Hawaii) under the collaboration with SUBARU Telescope. We observed the zodiacal light and the gegenschein in 2002 again, and got the excellent images. In this paper, we describe the design of WIZARD and report the performance examined by the laboratory measurements and the observations at Mauna Kea in 2002.

Numerical weather forecast at Mauna Kea Astronomical Observatory by Subaru telescope supercomputer

In order to operate large telescope, it is crucial to have a good weather forecast especially of the temperature when the telescope begins preparation, i.e., open the dome to introduce new fresh air inside. For this purpose, the Mauna Kea Weather Center (MKWC) has been established in July 1998 by the initiative of Institute of Astronomy, University of Hawaii. The weather forecast is not a simple matter and is difficult in general especially as in the quite unique environment as in the summit of Mauna Kea. MKWC introduced a system of numerical forecasting based on the mesoscale model, version five, so called MM5, was running on the vector parallel super computer VPP700 of Subaru Telescope for past three years. By the introduction of new supercomputer system at Subaru Telescope, we have prepared new programs for the new supercomputer systems. The long term but coarse grid forecast is available through National Center for Environmental Predict (NCEP) every day, and the MKWC system get the result of simulations on coarse grid over the pacific ocean from NCEP, and readjustment of data to the fine grid down to 1km spatial separation at the summit of Mauna Kea, i.e. Telescope sites of Mauna Kea Observatories. Computation begins around 20:00 HST, to end 48 hours forecast around 0100am next morning. Conversion to WWW graphics will finish around 0500am, then, the specialist of MKWC would take into the result of the numerical forecast account, to launch a precious forecast for the all observatories at the summit of Mauna Kea, at 10:00am HST. This is the collaboration among observatories to find a better observation environment.

The DIMM station at Subaru Telescope

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.

Improvement of the thermal environment around the Subaru Telescope enclosure

As the construction of the Subaru Telescope neared the end and the preparation of the first aluminum coating of the primary mirror on the ground floor of the telescope enclosure was in progress in 1997, dust particles blown into the enclosure became a serious issue. The source of the dust particles was mainly volcano cinder rocks in the immediate vicinity of the dome that were crushed through the construction activities, especially by heavy vehicle traffic around the dome. The mitigation measure proposed was to pave the immediate surrounding of the dome. The Subaru dome has a unique design with the special consideration to the airflow through the structure with a few ventilators for the best seeing condition possible. The heat retained by the pavement that may possibly cause thermals was an immediate concern. We examined several types of pavement materials to solve this problem and decided the most suitable materials and method. As a result, we paved the area using asphalt, and were able to improve seeing performance before midnight observation by painting the surface of pavement area white in 2003.

An experiment for developing a micro-crack alert system for large thin mirror

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.