Reizaburou Kitai

Performance of Software-Based Solar Adaptive Optics System

This paper reports the performance of our modified adaptive optics system for solar observations. This system operates at a frame rate of about 400 Hz and has the closed-loop cutoff frequency at 105 Hz. The results of the laboratory experiments show that this system compensates for a temporal wavefront-variation of less than 99 Hz and improves the Strehl ratio by a factor of five.

Solar adaptive optics system at the Hida Observatory

A solar adaptive optics system is developed for the 60 cm domeless solar telescope of the Hida Observatory in Japan. It is designed for compensating low order turbulence in G-band using a 52-electromagnetic-actuator deformable mirror, a 6x6 Shack-Hartmann wavefront sensor and standard personal computers. The details of the system, particularly features of the deformable mirror are described. Laboratory experiments show that the use of adaptive optics raises the Strehl ratio by a factor of five for turbulence of under 99Hz. In solar observations, the improvement of resolution in long-exposure images with the adaptive optics system is demonstrated.

Advances in solar adaptive optics system at the domeless solar telescope of the Hida Observatory

A solar adaptive optics system for the 60 cm domeless solar telescope of the Hida Observatory in Japan is developed. A high-speed deformable mirror with 52 electromagnetic actuators is newly used in an experimental adaptive optics system. The use of the mirror resulted in the improvement of Strehl ratios in laboratory experiments. In solar observations, the system worked well when solar granulation was used as a target for wavefront sensing. An adaptive optics system being developed for a vertical spectrograph of the domeless solar telescope is described.

Solar adaptive optics at the Hida Observatory: latest achievements of current system and design of new system

Solar adaptive optics (AO) systems are developed at the 60cm domeless solar telescope in the Hida Observatory, Japan. An AO system currently used has a deformable mirror with high-speed 97 electromagnetic actuators and a Shack- Hartmann wavefront sensor with a 10x10-microlens array and 4000fps-CMOS camera. Its control frequency is about 1100-1400 Hz, and hence the -3dB cutoff frequency of the system is theoretically above 100 Hz. In parallel to developing the system, a new full-scaled AO system is designed to be applicable to various observations, such as highdispersion spectroscopy and simultaneous wide-range spectroscopy. The new system will work as classical AO at first. The details of the current system, observational results using it, and the design of the new AO system are described.

Preliminary study of the evolution of solar magnetic structures and photospheric horizontal velocity fields

Abstract In October 1997, we made a coordinated observation of the solar photosphere and chromosphere at Hida observatory (Kyoto university, Japan) and at Teide observatory (Tenerife) over a 10 day. We obtained imaging data series continuously during 6 hr 45 min in G-band (4308 A) observed with the Domeless Solar Telescope (DST) at Hida on 24th October (effective FOV; 96″×99″). Additionally, in this observation, we simultaneously observed image series of the chromosphere during the latter 4 hr 10 min in H α line center and H α ±0.6 A. From these data set, we could detect that emerging flux tubes crossed the photosphere to the chromosphere and that ‘convective collapse’ phenomena appeared at the stage of the spot formation. Moreover, we confirmed that the lifetime of mesogranulation was about 4000 sec (70 min) from the temporal evolution of velocity patterns. We show here only a summary of these observations.

Optical setup and wavefront sensor for solar adaptive optics at the Domeless Solar Telescope, Hida Observatory

A solar adaptive optics system for a high-dispersion spectrograph is developed at the 60 cm domeless solar telescope of the Hida Observatory in Japan. Details of its optical setup are described for implementing a scanning slit spectroscopy with wavefront correction. A wavefront sensor used in the system is specified and a technique of reducing computational cost in wavefront sensing is also described. In solar observations, the improvement of contrast in images obtained with the adaptive optics system was demonstrated when a sunspot was used as a target of wavefront sensing.

Image acquisition and processing using a PC cluster toward real-time solar image improvement

This paper describes a PC-cluster-based observation system for improving the angular resolution of solar images. The system consists of two equipments separately working: one equipment realizes automatic acquisition of one hundred images at every fifteen seconds, and selects ten best images to be used in image processing. In the other one, image restoration and resolution improvement are carried out with a blind deconvolution method and a super-resolution method, respectively, using a PC cluster system. The system can take images at every fifteen seconds with high angular resolution. A test observation at the Hida Observatory confirmed a satisfactory performance of this system. The two equipments in the current hybrid system will be united in a future system that will realize image processing in pseudo-real time. A condition toward pseudo-real time processing is also investigated in this paper.

Horizontal Flow Field in the Solar Photosphere

A real-time frame selector (RTFS), a new observational system, was developed at the Domeless Solar Telescope of Hida Observatory, Kyoto University. RTFS allows automatic selection of a video frame with the highest spatial resolution in a series of live video images during a prescribed time span and stores it in digital format in a hard disk file. We applied the RTFS to observations of solar granulation in the g-band wavelength (λ 4308 A, passband 20 A), resulting in a time series of data with a time step of 15 sec. By a modified and simplified version of local-correlation tracking (November and Simon, 1988), we derived the horizontal velocity field using the granulation pattern as tracers. In the quiet photosphere, we clearly found a mesogranulation flow field (November et al., 1981) from a 70 min span of data on May 25, 1996 (Figure 1). Super-granular flow patterns were also detected and identified from comparison with an Hα wing image. Also, using RTFS on a sunspot area of NOAA7981 observed on Aug 2, 1996, we have found new evidence of horizontal inflow from penumbral areas to umbral areas and also the presence of another circumferential inflow from the surrounding photosphere to the penumbral outer edge (Figure 2). The inflow into the umbra is probably due to inflowing motions of penumbral grains found by Muller (1973).