Yoshikazu Nakatani

TEMPORAL EVOLUTION AND SPATIAL DISTRIBUTION OF WHITE-LIGHT FLARE KERNELS IN A SOLAR FLARE

On 2011 September 6, we observed an X2.1-class flare in continuum and H

Deconvolution of partially compensated solar images from additional wavefront sensing

\alpha

Development of a universal tunable filter for future solar observations

with a frame rate of about 30~Hz. After processing images of the event by using a speckle-masking image reconstruction, we identified white-light (WL) flare ribbons on opposite sides of the magnetic neutral line. We derive the lightcurve decay times of the WL flare kernels at each resolution element by assuming that the kernels consist of one or two components that decay exponentially, starting from the peak time. As a result, 42% of the pixels have two decay-time components with average decay times of 15.6 and 587 s, whereas the average decay time is 254 s for WL kernels with only one decay-time component. The peak intensities of the shorter decay-time component exhibit good spatial correlation with the WL intensity, whereas the peak intensities of the long decay-time components tend to be larger in the early phase of the flare at the inner part of the flare ribbons, close to the magnetic neutral line. The average intensity of the longer decay-time components is 1.78 times higher than that of the shorter decay-time components. If the shorter decay time is determined by either the chromospheric cooling time or the nonthermal ionization timescale and the longer decay time is attributed to the coronal cooling time, this result suggests that WL sources from both regions appear in 42% of the WL kernels and that WL emission of the coronal origin is sometimes stronger than that of chromospheric origin.

Development of a new solar adaptive optics system at the Hida Observatory

A technique for restoring solar images partially compensated with adaptive optics is developed. An additional wavefront sensor is installed in an adaptive optics system to acquire residual wavefront information simultaneously to a solar image. A point spread function is derived from the wavefront information and used to deconvolve the solar image. Successful image restorations are demonstrated when the estimated point spread functions have relatively high Strehl ratios.

Developments of the wideband spectropolarimeter of theDomeless Solar Telescope at Hida Observatory

We have developed a new narrowband tunable filter to perform imaging spectroscopy of the solar chromosphere. Using Liquid Crystal Variable Retarders (LCVRs) as the tuning elements for wavelength, wide-band polarizers and super achromatic half-wave plates, it is possible to make high speed tuning (about 0.1Sec), to exclude mechanical drives (and oil tank), and to cover a wide wavelength range (510-100nm). This filter builds up with seven stages each consisting of a pair of calcites, LCVR, half-wave plates and linear polarizer. The full width at half maximum (FWHM) of the filter transmission is about 0.025nm at 656.3nm.We demonstrate that the concept of the universal tunable filter using the LCVRs as tuning elements is highly promising for future application to space mission and ground based observations.

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

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.

The CHAIN-Project and Installation of Flare Monitoring Telescopes in Developing Countries

We developed a new universal spectropolarimeter on the Domeless Solar Telescope at Hida Observatory to realize precise spectropolarimetric observations in a wide range of wavelength in visible and near infrared. The system aims to open a new window of plasma diagnostics by using Zeeman effect, Hanle effect, Stark effect, and impact polarization to measure the external magnetic field, electric field, and anisotropies in atomic excitation in solar atmosphere. The polarimeter consists of a 60 cm aperture vacuum telescope, a high dispersion vacuum spectrograph, polarization modulator and analyser composed of a continuously rotating waveplate whose retardation is constant in 400 - 1100 nm and Wallaston prisms located closely behind the focus of the telescope, and a fast and high sensitive CCD camera or a infrared camera. The duration for this polarimeters achieving photometric accuracy of 10-3 is 30 - 60 s. Instrumental polarization of the telescope is calibrated by using a remotely controllable turret accommodating linear polarizer attached at the entrance window of the telescope to induce well known polarized light into the telescope. Thus a Mueller matrix model of the telescope is established to compensate the instrumental polarization included in observed data within the required accuracy.

Developments of a multi-wavelength spectro-polarimeter on the Domeless Solar Telescope at Hida Observatory

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.

Experiments of GLAO using the domeless solar telescope of the Hida Observatory

The Flare Monitoring Telescope (FMT) was constructed in 1992 at Hida Observatory in Japan to investigate the long-term variation of solar activity and explosive events. It has five solar imaging telescopes that simultaneously observe the full-disk Sun at different wavelengths around the H-alpha absorption line or in different modes. Therefore, the FMT can measure the three-dimensional velocity field of moving structures on the full solar disk. The science target of the FMT is to monitor solar flares and erupting filaments continuously all over the solar disk and to investigate correlation between the characteristics of the erupting phenomena and the geoeffectiveness of the corresponding coronal mass ejections (CMEs). We are planning to start up a new worldwide project, the Continuous H-alpha Imaging Network (CHAIN) project, as an important IHY project of our observatories. As part of this project, we are examining the possibility of installing telescopes similar to the FMT in developing countries. We have selected Peru and Algeria as the countries where the first and second overseas FMTs will be installed, and we are aiming to start operation of these FMTs by the end of 2010 before the maximum phase of solar cycle 24. To create such an international network, it will be necessary to improve the information technologies applied in our observation-system. In this paper, we explain the current status and future areas of work regarding our system.

Parallel processing of solar image restoration with phase diversity technique

To obtain full Stokes spectra in multi-wavelength windows simultaneously, we developed a new spectro-polarimeter on the Domeless Solar Telescope at Hida Observatory. The new polarimeter consists of a 60 cm aperture vacuum telescope on an altazimuth mount, an image rotator, a high dispersion spectrograph, polarization modulator and analyzer composed of a continuously rotating waveplate with a retardation nearly constant around 127