An adaptive optics (AO) system is developed for the 60cm domeless solar telescope of the Hida Observatory, Japan. Its performances are analyzed by the computer simulations, and improved by replacing the Zernike polynomials by Karhunen-Loève functions. Also, a tomographic wavefront sensor is developed for a ground-layer AO system. From test data acquired at the Hida observatory, wavefront-phase maps both in the ground-layer and in an upper layer are successfully derived.
We are developing a new adaptive optics (AO) system for the 60cm domeless solar telescope of the Hida Observatory, Japan. The system has a deformable mirror with 97 piezo-actuators, a Shack-Hartmann wavefront sensor with a 10×10-microlens array and standard personal computers. We conducted solar observations in September, 2013, and confirmed that our AO system cancelled image-shifts so that the deviations were within the resolution of the telescope. We report the detailed performances of our new AO system.
We developed a polarimeter for the ground-based solar observation using a high-speed rotating waveplate (typically
12.5–25 revolutions s−1) and a high-speed camera (typically 200–400 frames s−1) with commercially available
devices. Fast polarization modulation is required for the ground-based solar polarimetry to avoid producing
seeing-induced false polarization signals. Modulation with a high-speed rotating waveplate realizes not only fast
full-Stokes modulation but also wide coverage of the wavelength range, and therefore, a polarimeter with a highspeed
rotating waveplate is most suitable for the simultaneous polarimetry observations at multi-wavelengths
with a spectrograph. A comprehensive description of the instrument and some results of the solar spectropolarimetry
with this polarimeter are given in this paper.
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.
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.
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.
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.
We have developed a new digital imaging system for the Hα imager of the Solar Flare Telescope at Mitaka, NAOJ, for high-cadence observations of solar flares. To resolve individual spikes elementary bursts) of impulsive solar flares requires a time resolution within 1 s and a spatial resolution of about 1", and the high-speed Hα camera realized them. Such high-resolution observations produce huge amount of data, and it has been the major difficulty to construct a high-cadence system. Generally the amount of data from solar optical observations is huge, because they are multi-dimensional (in space/time/wavelength/polarization status). Efficient real-time processing of observational data is essentially important to extract meaningful information from the raw data. Recent advances in computer technology have made possible to handle vast data with a small computer. Therefore, firstly we have developed a PC-based flexible real-time image processing system, which is applicable to various real-time data processings required for solar optical observations. The high-speed Hα camera is developed based on this system. In this paper, the real-time image processing system and the high-speed Hα camera system are described as well as the actual operation of the Hα camera.
A high-speed video spectroheliograph was developed for imaging spectroscopy observations in multi-wavelength bands. It is attached to the focal plane of the spectrograph of the 60 cm Domeless Solar Telescope at Hida Observatory, Kyoto University. Although to take spectroheliograms needs some time to scan the solar image on the slit, a spectroheliograph gets spectral information co-temporally without suffering image blurrings by the seeing effect. Therefore, a spectroheliograph is suitable to obtain a data cube (spatial 2-D + spectral 1-D) for quantitative spectral analyses such as velocity field calculations. In our spectroheliograph system, up to three CCD video cameras can be attached to the spectrograph, and we can simultaneously observe up to three wavelength bands, for example, Ca II K/G-band/Hα,with three CCD video cameras, owing to the wide wavelength coverage of the spectrograph. Therefore, heliograms at different heights in the solar atmosphere can be obtained simultaneously. Images from the cameras are digitized by a frame grabber to 512 (4.3' along the slit) pixels × 256 (along the dispersion, typically 24 Å wide) lines and processed by a PC with a frame rate of 30 frames s-1. Therefore, it takes only 17 s to obtain a set of 512 × 512 pixel heliograms, which cover the field of view of 4.3'×4.3'.