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Author name code: kobiki
ADS astronomy entries on 2022-09-14
author:"Kobiki, Toshihiko"
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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
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<SUP>-1</SUP>. 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{^”<SUB>.</SUB>}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.
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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
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.
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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
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 MgF<SUB>2</SUB>
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. <P />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). <P />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.
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Title: Integral Field Spectroscopy of the Sun with Microlens Array
and Liquid Crystal Retarders
Authors: Suematsu, Y.; Shinoda, K.; Sano, I.; Kobiki, T.
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.
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Title: A Sounding Rocket Experiment for Spectropolarimetric
Observations with the Ly<SUB>α</SUB> 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.
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 Ly<SUB>α</SUB> 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 Ly<SUB>α</SUB> 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.
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Title: Sunspot magnetic fields observed with a large-format infrared
array
Authors: Sakurai, Takashi; Yanagisawa, Kenshi; Kobiki, Toshihiko;
Kasahara, Shouichi; Nakakubo, Kayoko
2003naoj.book...34S Altcode:
No abstract at ADS
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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
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 μI<SUB>o</SUB> (here I<SUB>o</SUB> is
the intensity of the solar disk center, and μI<SUB>o</SUB> means
I<SUB>o</SUB>×10<SUP>-6</SUP>). 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 μI<SUB>o</SUB>, could be a good
site for the observations of the Sun considering the transparency of
the sky.
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Title: Sunspot Magnetic Fields Observed with a Large-Format Infrared
Array
Authors: Sakurai, Takashi; Yanagisawa, Kenshi; Kobiki, Toshihiko;
Kasahara, Shouichi; Nakakubo, Kayoko
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 g<SUB>L</SUB> = 1.53) and 15652.9Å (g<SUB>L eff</SUB>
= 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..
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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.
1998RNAOJ...3..145N Altcode: 1998RNOAJ...3..145N
This report gives some results of γ-ray irradiation (Co<SUP>60</SUP>
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.
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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.
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 R<SUB>sun</SUB> and 2.0 R<SUB>sun</SUB>
by ≡80 km s-1 was found in the streamer.
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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
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.
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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.
1996mpsa.conf..413I Altcode: 1996IAUCo.153..413I
No abstract at ADS
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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.
1995pist.conf...72I Altcode:
No abstract at ADS
