Hydrogen Hα (656.2nm) and HeI 1083nm are the spectral lines most commonly used for diagnosing the solar chromosphere. We aim to investigate the scientific advantage in combining these lines in imaging spectroscopic observation using a narrowband tunable filter. Simultaneous imaging in two wavelengths is possible by splitting the light with a polarizing beam splitter attached at the exit of the filter and using two cameras. We have constructed a setup that enables spectroscopic imaging in Hα and HeI 1083nm lines almost simultaneously, with a time required for switching the wavelength of about 0.1 second. The full width at half maximum of the transmission in Hα is 0.25A, while, with an additional stage of the Lyot filter, it is 0.367A in HeI 1083nm. In this paper, we describe the overview of the system and demonstrate its observing capability by presenting some examples of observations. We also discuss the advantage of combining these two lines in view of their responses to the physical condition as inferred from a non-LTE calculation.
In order to derive solar magnetic fields, a 2D spectro-polarimeter working in the near-infrared wavelength range is under development. A voltage-wavelength-tunable lithium-niobate (LiNbO3) etalon filtergraph is used as the 2D spectrometer. A rotating waveplate for modulating the polarization is used, which has a nearly constant retardation of about 127 degrees over a wide wavelength range. The filtergraph consists of two etalons, 0.9 mm and 1.2 mm thick, optimized for ordinary ray transmission for both the He I 1083 nm chromospheric line and the photospheric magnetic-sensitive line of Fe I 1564 nm when used in tandem-etalon configuration. The etalons are Y-cut LiNbO3 wafers coated with reflective and conductive (ITO) layers. A linear polarizer between the rotating retarder and the filtergraph functions as a polarization analyzer and selects the ordinary ray transmission. We carried out polarization observations of solar active regions at several wavelength points in the He I 1083 nm line with a high-speed IR camera at Hida Observatory, Kyoto University. Some observational results together with the instrumental properties are presented.
We describe newly developed voltage-tunable lithium-niobate (LiNbO3) Fabry-Perot etalons for solar near-infrared filtergraph. Two etalons were fabricated for tandem use: One etalon is 0.9 mm thick and the other is 1.2 mm thick, optimized in ordinary ray transmission for both He I 1083.035 nm and magnetic sensitive Fe I 1564.85 nm lines. The etalons are Y-cut lithium-niobate wafers coated with highly reflective and conductive (ITO) layers. We examined optical and voltage-tunable properties of the etalons using the horizontal spectrograph of the Domeless Solar Telescope at Hida Observatory, Kyoto University. Some solar observations with tandem etalons were also ran and their good imaging quality was demonstrated. Some results from the measurements are reported.
We report experiments of solar ground-layer (GL) adaptive optics (AO) using the 60cm domeless solar telescope of the Hida Observatory, Japan. We developed an averaging-type GL wavefront sensor and confirmed that it properly worked in computer simulations. We set the wavefront sensor behind a conventional AO system and modified AO software so as to drive a deformable mirror using the GL sensor. We conducted solar observations with the GLAO system in September, 2017. It worked to improve observational images over wide fields.
We aim at improving solar images partially compensated by Adaptive Optics (AO) or Ground-Layer (GL) AO using a phase diversity (PD) method. To reduce computational time in the PD execution, we develop a computer cluster system that enables restoration of several images in parallel. We set a PD-observational system downstream of an AO system in the Hida Observatory in Japan. Driving the AO system, we recorded focused and defocused solar images. They were segmented to partial images, and then were restored by the PD method. We show the results of solar image restoration, and also demonstrate the reduction of processing time by the computer cluster.
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 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 polarimeter's 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.
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.
In order to perform precise and high time cadence magnetic field measurement across the solar surface, the Tandem
Fabry-Perot filter imaging spectro-polarimeter for the Solar Magnetic Activity Research Telescope (SMART) is revised.
By using the CCD with moderate frame rate of 30fps, full Stokes vectors on the field-of-view 320"x240" can be obtained
at 4 wavelengths around FeI6302 line within about 15s. The optical performance of the Tandem Fabry-Perof filters is
investigated by using the spectrograph at the Domeless Solar Telescope at Hida Observatory. The test results show the
full-width-half-maximum (FWHM) of the tandem filters is about 0.017nm over the 60mm clear aperture is achieved. The
system is developed to start the regular observations from 2010.
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.
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.
In recent years, it is beginning to be shown observationally and theoretically that the existence of the magnetic field is
indispensable for active phenomena on the solar surface. In particular, the rotation or helicity of the magnetic field and
their temporal variation are considered to be important factors which influence solar activity. In order to confirm this, it
is necessary to compute vector components of the magnetic field with a higher accuracy than before. Therefore, we developed two kinds of filter-type magnetographs for the Solar Magnetic Activity Research Telescope (SMART) at Hida observatory, which allow us to observe the polarization components in sunlight with high accuracy. We use a Lyot filter in one of two sets of magnetographs. On the other hand, a tandem-typed Fabry-Perot filter is used in one more set. For these two instruments, we made the following concrete advances. 1. The method of coating of the pre-filters. 2. Special fine-anneal on the main lenses. 3. Highly accurate rotating wave-plate. 4. Simultaneous observation of two kinds of filtergrams which have orthogonally polarized light mutually by using Fabry-Perot channel. 5. Observation in four wavelengths which can suppress various errors.
6. Low apparent Doppler shift in the FOV due to the oblique incidence of the rays to the filters. 7. Large format CCD (large-sized chip, large full-well). 8. High speed data transfer interface between the CCD and PC. In this paper, we report the details of these points, the expected effect of them, and the results of initial measurements.
A new spectropolarimeter is developed at the Domeless Solar Telescope
(DST) in Hida Observatory. It consists of a rotating waveplate, Wollaston prisms, and a high-dispersion spectrograph which is vertically installed at the focus of the DST. In order to realize a high-precision measurement, it is inevitable to compensate the instrumental polarization due to the DST. We observed the quiet region of the Sun, which is considered to be highly unpolarized, with and without a sheet linear polarizer or circular polarizer set at the entrance window of the telescope. The theoretical model which represents the total instrumental polarization of the DST with some characteristic parameters was calculated and compared with the observation. The model that two flat mirrors have different properties can explain the observation in 0.5% accuracy for the unpolarized light, and in 7% for the polarized light.
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