Masao Nakagiri

SOLAR NEUTRON EVENTS THAT HAVE BEEN FOUND IN SOLAR CYCLE 23

In this paper, we report solar neutron events detected in the solar cycle 23, especially three interesting events detected on November 23rd and 28th 1998 in Tibet and October 28th 2003 in Tsumeb.

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.

Cleaning procedure for mirror coating at Subaru Telescope

We would like to present the procedure of how to prepare the primary mirror of Subaru Telescope for the realuminization. The equipment for the coating and its preparation are located at the ground floor of the telescope enclosure. There are two trolleys for carrying the mirror cell and the mirror itself, a mirror lifting jig, a washing facility for the primary mirror (PMWF), the water purification system, the coating chamber and the waste water pit. The PMWF can provide the tap water for initial rinsing, the chemical for stripping the old coating, and the deionized water for final cleaning. It has two pairs of arms that deploy horizontally above the mirror and have nozzles to spray. The arms spin around its center where the rotary joints are connected to the plumbing from storage tanks. Deck above the water arms serve as platform for personnel for the inspection or for scrubbing work. We use hydrochloric acid mixture to remove the old aluminum coating. For rinsing and final cleaning, we use the water through the purification system. The water supply from the nozzles and the rotation of the arms can be controlled from a panel separated from the washing machine itself. After several experiments and improvements in the washing, we have carried out the coating of the 8.3 m primary mirror in September last year. This was the third time, and the reflectivity of the new coating show satisfactory result.

Status of the coating facility of the Subaru Telescope

One of the major problems to retain the efficiency of a telescope is to achieve and maintain high reflectivity in the wide wavelengths of the coatings of the telescope optics. For coating the large mirrors of Subaru Telescope, we employed the conventional evaporation scheme, in the expectation of uniform coverage of the film. In this paper, we will report the installation and the performance verification of the coating facility. This facility consists of a washing tower for stripping off the old coating, an evaporation coating chamber, two trolleys and a scissors- like lifter for handling the primary mirror. To supply a large number of filaments loaded with uniform quality molten metal, the practical solution is to pre-wet the filaments with the agent metal and keep them in a controlled manner before the evaporation. The aluminum film deposit on the test samples in the 8.3 m coating chamber proved the film thickness uniformity matching with the specification. Reflectivity of the fresh surface was over 90% at visible wavelength. In September 1997, we re-aluminized 1.6 m and 1.3 m mirrors for the first time (at least for ourselves) application to the real astronomical telescopes. The resultant surface reflectivity confirmed the feasibility of using pre-wetted filaments.

Evaluation of the JNLT Site

Two steps have been taken to decide at what place and altitude to set up the JNLT on Mauna Kea. First, the wind tunnel experiment has been made in collaboration with the Institute of Meteorology using the two models of summit area with the reduced scales of 1/1000 and 1/5000. This study tells us that the north-west cone is suitable for JNLT. Secondly, we have done the measurement of the microthermal activities in this area with a 30 m tower, which was continued for about 4 months in collaboration with the University of Hawaii. This experiment has given the mean vertical profile of (math) over 4 months and its scale height in the boundayr layer on our site. By use of these measurements, the contribution of the boundary layer to seeing is estimated. The behaviour of (math) under strong winds can be explained very well by topographic effects, which is in fairly good agreement with the results of our wind tunnel experiment.

Performance of 10-100 GeV gamma ray camera for SUBARU optical-infared telescope

We developed the gamma-ray camera for SUBARU infrared-optical telescope, named CheSS (Cherenkov light detecting System on Subaru). The CheSS was designed based on Imaging Atmospheric Cherenkov Technique (IACT) which has been established by detections of high energy gamma-ray sources in the last decade. According to our Monte Carlo simulation, the energy thresholds of the CheSS for the Crab are 30 GeV at zenith angle of 10 degrees, and the expected sensitivity for the unpulsed component can reach ~10σ level and more for pulsed one during 10 hours on-source pointing.

Coating and cleaning of the Subaru Telescope mirrors

After the initial coating of the 8.3-m primary mirror of the Subaru Telescope in November 1998, we have conducted the first re-aluminization in August 1999. The primary mirror washing fixture worked efficiently for stripping the old coating and for washing the surface. Dry process is still to be improved. Suite of secondary and tertiary mirrors are being tested at the telescope, two of which were coated in- house, one in silver for the infrared observations and the other in aluminum for the optical observations, respectively. Evaluation of the coating film is conducted in two methods. Using a portable microScan, the reflectivity and the BRDF numbers of the primary mirror is monitored. Reflectivity over a wide range of the wavelength is measured in the witness mirrors. The preliminary data shows reasonably good number for the telescope optics. The in-situ cleaning of the primary mirror with solid and gaseous CO2 sprinkle arms is operating once every month. Next step for the coating chamber commissioning is to improve the heating capacity for silver coating of the infrared secondary and tertiary mirrors, and the experiment for silver coating is going.