Author name code: kobiki ADS astronomy entries on 2022-09-14 author:"Kobiki, Toshihiko" ------------------------------------------------------------------------ Title: Infrared spectro-polarimeter on the Solar Flare Telescope at NAOJ/Mitaka Authors: Sakurai, Takashi; Hanaoka, Yoichiro; Arai, Takehiko; Hagino, Masaoki; Kawate, Tomoko; Kitagawa, Naomasa; Kobiki, Toshihiko; Miyashita, Masakuni; Morita, Satoshi; Otsuji, Ken'ichi; Shinoda, Kazuya; Suzuki, Isao; Yaji, Kentaro; Yamasaki, Takayuki; Fukuda, Takeo; Noguchi, Motokazu; Takeyama, Norihide; Kanai, Yoshikazu; Yamamuro, Tomoyasu Bibcode: 2018PASJ...70...58S Altcode: 2018PASJ..tmp...63S; 2018PASJ..tmp...82S An infrared spectro-polarimeter installed on the Solar Flare Telescope at the Mitaka headquarters of the National Astronomical Observatory of Japan is described. The new spectro-polarimeter observes the full Sun via slit scans performed at two wavelength bands, one near 1565 nm for a Zeeman-sensitive spectral line of Fe I and the other near 1083 nm for He I and Si I lines. The full Stokes profiles are recorded; the Fe I and Si I lines give information on photospheric vector magnetic fields, and the helium line is suitable for deriving chromospheric magnetic fields. The infrared detector we are using is an InGaAs camera with 640 × 512 pixels and a read-out speed of 90 frames s-1. The solar disk is covered by two swaths (the northern and southern hemispheres) of 640 pixels each. The final magnetic maps are made of 1200 × 1200 pixels with a pixel size of 1{^''.}8. We have been carrying out regular observations since 2010 April, and have provided full-disk, full-Stokes maps, at the rate of a few maps per day, on the internet. Title: High-Reflectivity Coatings for a Vacuum Ultraviolet Spectropolarimeter Authors: Narukage, Noriyuki; Kubo, Masahito; Ishikawa, Ryohko; Ishikawa, Shin-nosuke; Katsukawa, Yukio; Kobiki, Toshihiko; Giono, Gabriel; Kano, Ryouhei; Bando, Takamasa; Tsuneta, Saku; Auchère, Frédéric; Kobayashi, Ken; Winebarger, Amy; McCandless, Jim; Chen, Jianrong; Choi, Joanne Bibcode: 2017SoPh..292...40N Altcode: Precise polarization measurements in the vacuum ultraviolet (VUV) region are expected to be a new tool for inferring the magnetic fields in the upper atmosphere of the Sun. High-reflectivity coatings are key elements to achieving high-throughput optics for precise polarization measurements. We fabricated three types of high-reflectivity coatings for a solar spectropolarimeter in the hydrogen Lyman-α (Lyα ; 121.567 nm) region and evaluated their performance. The first high-reflectivity mirror coating offers a reflectivity of more than 80 % in Lyα optics. The second is a reflective narrow-band filter coating that has a peak reflectivity of 57 % in Lyα , whereas its reflectivity in the visible light range is lower than 1/10 of the peak reflectivity (∼5 % on average). This coating can be used to easily realize a visible light rejection system, which is indispensable for a solar telescope, while maintaining high throughput in the Lyα line. The third is a high-efficiency reflective polarizing coating that almost exclusively reflects an s-polarized beam at its Brewster angle of 68° with a reflectivity of 55 %. This coating achieves both high polarizing power and high throughput. These coatings contributed to the high-throughput solar VUV spectropolarimeter called the Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP), which was launched on 3 September, 2015. Title: Precision VUV Spectro-Polarimetry for Solar Chromospheric Magnetic Field Measurements Authors: Ishikawa, R.; Bando, T.; Hara, H.; Ishikawa, S.; Kano, R.; Kubo, M.; Katsukawa, Y.; Kobiki, T.; Narukage, N.; Suematsu, Y.; Tsuneta, S.; Aoki, K.; Miyagawa, K.; Ichimoto, K.; Kobayashi, K.; Auchère, F.; Clasp Team Bibcode: 2014ASPC..489..319I Altcode: The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a VUV spectro-polarimeter optimized for measuring the linear polarization of the Lyman-α line (121.6 nm) to be launched in 2015 with NASA's sounding rocket (Ishikawa et al. 2011; Narukage et al. 2011; Kano et al. 2012; Kobayashi et al. 2012). With this experiment, we aim to (1) observe the scattering polarization in the Lyman-α line, (2) detect the Hanle effect, and (3) assess the magnetic fields in the upper chromosphere and transition region for the first time. The polarization measurement error consists of scale error δ a (error in amplitude of linear polarization), azimuth error Δφ (error in the direction of linear polarization), and spurious polarization ɛ (false linear polarization signals). The error ɛ should be suppressed below 0.1% in the Lyman-α core (121.567 nm ±0.02 nm), and 0.5% in the Lyman-α wing (121.567 nm ±0.05 nm), based on our scientific requirements shown in Table 2 of Kubo et al. (2014). From scientific justification, we adopt Δ φ<2° and δ a<10% as the instrument requirements. The spectro-polarimeter features a continuously rotating MgF2 waveplate (Ishikawa et al. 2013), a dual-beam spectrograph with a spherical grating working also as a beam splitter, and two polarization analyzers (Bridou et al. 2011), which are mounted at 90 degree from each other to measure two orthogonal polarization simultaneously. For the optical layout of the CLASP instrument, see Figure 3 in Kubo et al. (2014). Considering the continuous rotation of the half-waveplate, the modulation efficiency is 0.64 both for Stokes Q and U. All the raw data are returned and demodulation (successive addition or subtraction of images) is done on the ground.

We control the CLASP polarization performance in the following three steps. First, we evaluate the throughput and polarization properties of each optical component in the Lyman-α line, using the Ultraviolet Synchrotron ORbital Radiation Facility (UVSOR) at the Institute for Molecular Science. The second step is polarization calibration of the spectro-polarimeter after alignment. Since the spurious polarization caused by the axisymmetric telescope is estimated to be negligibly small because of the symmetry (Ishikawa et al. 2014), we do not perform end-to-end polarization calibration. As the final step, before the scientific observation near the limb, we make a short observation at the Sun center and verify the polarization sensitivity, because the scattering polarization is expected to be close to zero at the Sun center due to symmetric geometry. In order to clarify whether we will be able to achieve the required polarization sensitivity and accuracy via these steps, we exercise polarization error budget, by investigating all the possible causes and their magnitudes of polarization errors, all of which are not necessarily verified by the polarization calibration. Based on these error budgets, we conclude that a polarization sensitivity of 0.1% in the line core, δ a<10% and Δ φ<2° can be achieved combined with the polarization calibration of the spectro-polarimeter and the onboard calibration at the Sun center(refer to Ishikawa et al. 2014, for the detail).

We are currently conducting verification tests of the flight components and development of the UV light source for the polarization calibration. From 2014 spring, we will begin the integration, alignment, and calibration. We will update the error budgets throughout the course of these tests. Title: Integral Field Spectroscopy of the Sun with Microlens Array and Liquid Crystal Retarders Authors: Suematsu, Y.; Shinoda, K.; Sano, I.; Kobiki, T. Bibcode: 2011AGUFMSH13B1947S Altcode: Simultaneous spectrographic observations over extended solar structures, at a high spatial resolution and temporal cadence, are important to track and understand the physics of transient phenomena such as Ellerman bombs, flare kernels, prominences/filaments and spicules. With two-dimensional (2-D) field spectral data, we can make monochromatic images at a given wavelength in a designed passband and line profile analysis to derive 2-D distribution of atmospheric parameters. One technique to produce a spectrum of each spatial elements in an extended two-dimensional field is to use a micro-lens array. Replacing a slit of a conventional spectrograph with a micro-lens array then helps to capture two-dimensionally distributed short spectra from 2-D field using additional optics inserted, a bandpass filter and a large format detector. For observations of magnetic field, we can add polarization modulator made of liquid crystal retarders which give a sequence of alternative orthogonal polarization states with time. We describe a design concept and limitations for observations with the micro-lens array spectrograph and an initial result applied for a few existing solar telescopes at NAOJ and Hida Observatory, Kyoto University. Title: A Sounding Rocket Experiment for Spectropolarimetric Observations with the Lyα Line at 121.6 nm (CLASP) Authors: Ishikawa, R.; Bando, T.; Fujimura, D.; Hara, H.; Kano, R.; Kobiki, T.; Narukage, N.; Tsuneta, S.; Ueda, K.; Wantanabe, H.; Kobayashi, K.; Trujillo Bueno, J.; Manso Sainz, R.; Stepan, J.; de Pontieu, B.; Carlsson, M.; Casini, R. Bibcode: 2011ASPC..437..287I Altcode: A team consisting of Japan, USA, Spain, and Norway is developing a high-throughput Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP), which is proposed to fly with a NASA sounding rocket in 2014. CLASP will explore the magnetism of the upper solar chromosphere and transition region via the Hanle effect of the Lyα line for the first time. This experiment requires spectropolarimetric observations with high polarimetric sensitivity (∼0.1%) and wavelength resolution (0.1 Å). The final spatial resolution (slit width) is being discussed taking into account the required high signal-to-noise ratio. We have demonstrated the performance of the Lyα polarimeter by extensively using the Ultraviolet Synchrotron ORbital Radiation Facility (UVSOR) at the Institute for Molecular Sciences. In this contribution, we report these measurements at UVSOR together with the current status of the CLASP project. Title: Sunspot magnetic fields observed with a large-format infrared array Authors: Sakurai, Takashi; Yanagisawa, Kenshi; Kobiki, Toshihiko; Kasahara, Shouichi; Nakakubo, Kayoko Bibcode: 2003naoj.book...34S Altcode: No abstract at ADS Title: Observations of the Mie scattered light intensities around the Sun with a portable coronagraph Authors: Tanaka, Nobuyuki; Kobiki, Toshihiko; Saito, Moriya; Shinoda, Kazuya; Irie, Makoto Bibcode: 2002RNAOJ...6...11T Altcode: Measurements of Mie scattering intensites around the Sun have been carried out by using a 5 cm coronagraph at (1) Chichijima, Ogasawara Islands, (2) Shiiba, Miyazaki prefecture, (3) Kitadaito Island, Okinawa, (4) Hateruma Islands, Okinawa, and (5) Saku Island, Aichi prefecture. Although our observations were limited in time for only a few days, the results indicate that the solar corona may be observable even at an altitude of 1,000m or less (for example at Shiiba, Miyazaki) where the intensity of scattered light is eventually less than 100 μIo (here Io is the intensity of the solar disk center, and μIo means Io×10-6). Comparison among the tested sites is diffucult because the measurements were done in various seasons in the year; and monitoring over longer time period is necessary to derive definite conclusions. However, the sites where the scattered light intensity is stable and less than 100 μIo, could be a good site for the observations of the Sun considering the transparency of the sky. Title: Sunspot Magnetic Fields Observed with a Large-Format Infrared Array Authors: Sakurai, Takashi; Yanagisawa, Kenshi; Kobiki, Toshihiko; Kasahara, Shouichi; Nakakubo, Kayoko Bibcode: 2001PASJ...53..923S Altcode: Spectro-polarimetric observations of sunspots were carried out by using a PtSi near-infrared camera (KONIC) of Kiso Observatory, The University of Tokyo, in the period of 1999 November 3-5. The camera was attached to a spectrograph of the Domeless Solar Telescope at Hida Observatory, Kyoto University. We observed the absorption lines of FeI at 15648.5Å (Lande factor gL = 1.53) and 15652.9Å (gL eff = 3), and derived the distribution of the magnetic field strengths and inclination angles across the sunspots. The ratio of the Zeeman splitting of the two lines was derived to be 0.39 +/- 0.01, while the ratio of the Lande factors is 0.51. Our data indicates that the effective Lande factor of the 15652.9Å line is 1.17 +/- 0.03.. Title: Radiation testing of optical glasses and crystals for Solar-B optical instruments. Authors: Nishino, Y.; Suematsu, Y.; Tsuneta, S.; Ichimoto, K.; Kobiki, T.; Takeyama, N. Bibcode: 1998RNAOJ...3..145N Altcode: 1998RNOAJ...3..145N This report gives some results of γ-ray irradiation (Co60 source) testing on optical glasses and crystals which may be used in the next Japanese solar space mission Solar-B. Ordinary optical glasses darken when exposed to high-energy radiation which is present in natural space environment. In case of Solar-B, whose orbit will be polar-sun-synchronous, the satellite will undergo the total dose of more than 1000 krad in five years. Hence it is very crucial for the success of the mission to know the feasibility of transmitting optical elements in space. The authors tested two kinds of fused silica, a fluorite, and ten kinds of UV transmitting glasses. Calcite was also tested. It was found that the fused silica is radiation-resistant but the other glasses and the fluorite are nonresistant and become quite opaque in UV and visible wavelength regions after the irradiation. Title: Measurement of the coronal electron temperature at the total solar eclipse on 1994 November 3. Authors: Ichimoto, K.; Kumagai, K.; Sano, I.; Kobiki, T.; Sakurai, T.; Munoz, A. Bibcode: 1997ASIC..494...31I Altcode: 1997topr.conf...31I The coronal electron temperature was determined for the first time from the shape of weak depressions at 3900 Å and 4300 Å in the continuous coronal spectra. It was found that the coronal streamer has overall temperatures of about 1.5 - 1.7 MK, while the coronal hole has evidently lower temperature of 0.9 - 1.1 MK. No significant height variation of the temperature was found in the streamer, while the coronal hole shows evidence of increasing temperature with height. An acceleration of the expanding motion between 1.1 Rsun and 2.0 Rsun by ≡80 km s-1 was found in the streamer. Title: Measurement of the Coronal Electron Temperature at the Total Solar Eclipse on 1994 November 3 Authors: Ichimoto, Kiyoshi; Kumagai, Kazuyoshi; Sano, Issei; Kobiki, Toshihiko; Munoz, Alberto; Sakurai, Takashi Bibcode: 1996PASJ...48..545I Altcode: A spectroscopic observation was carried out at the total solar eclipse on 1994 November 3 in Putre, Chile, in order to investigate the electron temperature and the expanding motion of the corona. The shape of weak depressions at 3900 Angstroms and 4300 Angstroms in the continuous coronal spectra was compared with the theoretical electron-scattered coronal spectra; thus, the magnitude of the electron thermal motion was determined directly. It was found that a coronal streamer on the eastern limb and a coronal hole on the south-pole have overall temperatures of about 1.5--1.7 MK and 0.9--1.1 MK, respectively. No significant height variation in the temperature was found in the streamer, while the coronal hole shows evidence of increasing temperature with height. An acceleration of the expanding motion between 1.1 RO and 2.0 RO by ~ 80 km s(-1) was found in the streamer. Title: Measurement of the Coronal Electron Temperature at the Total Solar Eclipse on 3rd Nov. 1994 Authors: Ichimoto, K.; Kumagai, K.; Sano, I.; Kobiki, T.; Sakurai, T.; Munoz, A. Bibcode: 1996mpsa.conf..413I Altcode: 1996IAUCo.153..413I No abstract at ADS Title: Measurement of the Coronal Electron Temperature at the Total Solar Eclipse on November 3, 1994 Authors: Ichimoto, K.; Kumagai, K.; Sano, Y.; Kobiki, T.; Sakurai, T.; Munos, A. Bibcode: 1995pist.conf...72I Altcode: No abstract at ADS