• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.31.4-32
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• 2016

Observing the solar atmosphere with ground-based telescopes in the near-infrared has a number of advantages when compared to classical measurements in visible wavelengths. One of them comes from the magnetic sensitivity of spectral lines, which varies as ${\lambda}_g$, where g is the effective $Land{\acute{e}}$ factor of the transition. This wavelength dependence makes the near-infrared range adequate to study subtle spatial or temporal variations of the magnetic field. Spectral lines, such as the photospheric Fe I $1.5648{\mu}m$ spectral line, with a $Land{\acute{e}}$ factor g=3, have often been used in the past for this type of studies. To study the chromosphere, the Ca II IR triplet and the He I $1.0830{\mu}m$ triplet are the most often observed lines. The latter has the additional advantage that the photospheric Si I $1.0827{\mu}m$ is close enough so that photosphere and chromosphere can be simultaneously recorded with a single detector in a spectrograph. The instrument TIP (Tenerife Infrared Polarimeter) has been continuously operating since 1999 at the 70-cm German VTT of the Observatorio del Teide and has been recently moved to the 1.5-m German GREGOR. During all this time, results have been obtained concerning the nature of the weak photospheric magnetic field of the quiet sun, magneto-acoustic wave propagation, evolution with the cycle of sunspot magnetic fields, photospheric and chromospheric magnetic field in emerging regions, magnetic field in chromospheric structures such as filaments, prominences, flares, and spicules, etc. In this talk, I will review the main results obtained after all these observations and mention the main challenges for the future. With its novel polarization-free design and a complete suite of instruments aimed at simultaneous (imaging and spectroscopic) observations of the solar photosphere and chromosphere, the EST (European Solar Telescope) will represent a major world-wide infrastructure to understand the physical nature of all these phenomena.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.53.2-53.2
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• 2014

IGRINS, the Immersion GRating INfrared Spectrometer, is a near-infrared wide-band high-resolution spectrograph jointly developed by the Korea Astronomy and Space Science Institute and the University of Texas at Austin. IGRINS employs three HAWAII-2RG focal plane array (FPA) detectors. The mechanical mounts for these detectors serves a critical function in the overall instrument design: Optically, they permit the only positional compensation in the otherwise "build to print" design. Thermally, they permit setting and control of the detector operating temperature independently of the cryostat bench. We present the design and fabrication of the mechanical mount as a single module. The detector mount includes the array housing, a housing for the SIDECAR ASIC, a field flattener lens holder, and a support base. The detector and ASIC housing will be kept at 65 K and the support base at 130 K. G10 supports thermally isolate the detector and ASIC housing from the support base. The field flattening lens holder attaches directly to the FPA array housing and holds the lens with a six-point kinematic mount. Fine adjustment features permit changes in axial position and in yaw and pitch angles. We optimized the structural stability and thermal characteristics of the mount design using computer-aided 3D modeling and finite element analysis. Based on the computer simulation, the designed detector mount meets the optical and thermal requirements very well.

• Journal of The Korean Astronomical Society
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• v.28 no.2
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• pp.245-253
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• 1995

We have analyzed the time series of Ca II H,K and ${\lambda}8498$ line profiles taken for a sunspot (SPO 5007) with the Echelle spectrograph attached to Vacuum Tower Telescope at Sacramento Peak Solar Observatory. Each set of spectra was taken simultaneously for 20 minutes at a time interval of 30 seconds. A total of 40 photographic films for each line was scanned by a PDS at Korea Astronomy Observatory. The central peak intensity of Ca II H ($I_{max}$), the intensity measured at ${\Delta}{\lambda}=-0.1{\AA}$ from the line center of ${\lambda}8498(I_{{\lambda}8489})$, the radial velocity ($V_r$) and the Doppler width (${\Delta}{\lambda}_D$) estimated from Ca II H have been measured to study the dynamical behaviors of the sunspot chromosphere. Fourier analysis has been carried out for these measured quantities. Our main results are as follows: (1) We have confirmed the 3-minute oscillation being dominant throughout the umbra. The period of oscillations jumps from 180 sec in the umbra to 500 to 1000 sec in the penumbra. (2) The nonlinear character of the umbral oscillation is noted from the observed sawtooth shaped radial velocity fluctuations with amplitudes reaching up to $5{\sim}6\;km/sec$. (3) The spatial distribution of the maximum powers shows that the power of oscillations is stronger in the umbra than in the penumbra. (4) The spatial distributions of the time averaged < $I_{max}$ > and < $V_r$ > across the spot are found to be nearly axially symmetric, implying that the physical quantities derived from the line profiles of Ca II H and ${\lambda}8498$ are inherently associated with the geometry of the magnetic field distribution of the spot. (5) The central peaks of the CaII H emission core lead the upward motions of the umbral atmosphere by $90^{\circ}$, while no phase delay is found in intensities between $I_{max}$ and $I_{{\lambda}8498}$, suggesting that the umbral oscillation is of standing waves.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.111.2-111.2
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• 2012

We observed an Ellerman bomb(EB) and its associated surge using the Fast Imaging Solar Spectrograph(FISS) and the broadband TiO filter of the 1.6 meter New Solar Telescope at Big Bear Solar Observatory. As is well-known, the EB appears as a feature that is very bright at the far wings of the H alpha line. The lambdameter method applied to these wings indicates that the EB is blue-shifted up to 6km/s in velocity. In the photospheric level below the EB, we see rapidly growing "granule-like" feature. The transverse velocity of the dark lane at the edge of the "granule" increased with time as reached a peak of 6km/s, at the time of the EB's occurrence. The surge was seen in absorption and varied rapidly both in the H alpha and the Ca II 8542 line. It originated from the Ellerman bomb, and was impulsively accelerated to 20km/s toward us(blueshift). Then the velocity of the surge gradually changed from blueshift of 20km/s to redshift of 40km/s. By adopting the cloud model, we estimated the temperature of the surge material at about 27000K and the non-thermal velocity at about 10km/s. Our results shed light on the conventional idea that an EB results from the magnetic reconnection of an emerging flux tube and pre-existing field line.

• The Journal of Korean Academy of Prosthodontics
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• v.18 no.1
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• pp.49-57
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• 1980

The adhesive mechanisms on the metal-ceramic restorations have been reported to be mechanical interlocking, chemical bonding, compressive force, and Van der Waal's force, etc. Of these, the mechanical interlocking and chemical bonding forces are thought to affect the adhesive force between Ni-Cr alloy and porcelain. This study investigates the adhesion of Ni-Cr alloy to porcelain according to surface treatment. For this purpose, the following experiments were made; The compositions of Ni-Cr alloy as cast by emission spectrograph, and the oxides produced on Ni-Cr alloy during degassing at $1850^{\circ}F$ for 30 minutes in air and in vacuum were analyzed by X-ray diffractograph. The metal phases of Ni-Cr alloy were observed according to porcelain-baking cyclic heat treatment by photo microscope and the distribution and the shift of elements of Ni-Cr alloy and porcelain and the failure phases between Ni-Cr alloy and porcelain by scanning electron microscope. The adhesive force between Ni-Cr alloy and porcelain was measured according to surface treatment with oxidization and roughening by Instron Universal Testing Machine. Results were as follows; 1. The metal phases of Ni-Cr alloy as cast and degassing state showed the enlarged and fused core, but when subjected to porcelain-baking cyclic heat treatment, showed a dendrite growing. 2. The kinds of metal oxides produced on Ni-Cr alloy during degassing were found to be NiO and $Cr_2O_3$. 3. The distribution of elements at the interface of Ni-Cr alloy and porcelain in degassing state showed demarcation line, but in roughening state, showed mechanical interlocking phase. 4. The shift of elements at the interface occurred in both states, but the shift amount was found to be larger in roughening than in degassing. 5. The adhesive force between Ni-Cr alloy and porcelain was found to be $3.45{\pm}0.93kg/mm^2$, in degassing and $3.82{\pm}0.99kg/mm^2$, in roughening. 6. The failure phase between Ni-Cr alloy and porcelain showed the mixed type failure.

• Economic and Environmental Geology
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• v.8 no.4
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• pp.183-201
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• 1975

The south and southwestern parts of Jeonra-namdo has been known as an alunite province in Korea. The alunite deposits investigated for the present study are Okmaisan, Seongsam, Bugog, Gasado south, Gasado north, Jangsando, Dogcheon and Jungyongri deposits. The main purpose of this study is to depict the genetical origin of the alunite deposits. The rocks distributed in the areas mentioned above consist chiefly of rhyolitic tuff, breccia tuff and andesitic tuff of Cretaceous age which represent different episodes of volcanic activities during Cretaceous epoch. The attitude of bedding of the tuffaceous rocks varies from place to place but generally dips very gently. The alunite deposits are embedded mostly in the rhyolitic tuff so that they appear as layered deposits, this occurrence may be the result of stratigraphic and lithologic controls. The result of this study can be summarized as below. The mineral sequence studied by the mineral paragenesis and the result of the spectrograph anlyses is such that (1) alunite was formed at first and pyrophyllite was nearly contemporaneous with alunite but pyrophyllite formation can be recognized as a secondary mineralization products, (2) kaoline was succeeded to form later and hematite finally deposited, and (3) pyrite was deposited from the begining to the end of the above mineralization period. The compositional change of host rocks is such that CaO, $SiO_2$ and $Na_2O$ were largely removed from the parent rocks and some $Al_2O_3$ and $SO_3$ were transported by the solution so as to enrich the rocks. The sequencial process of such mineralization has resulted in forming those distinguish mineral zones; alunite, kaoline, pyrophyllite, silicifide and sulphide zone which manifest irregular shape. These deposits were formed by hydrothermal solution which was possibly low temperature and contained sulphuric acid originated from $H_2S$ and $SO_2$ gases.

• Journal of Astronomy and Space Sciences
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• v.19 no.4
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• pp.283-292
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• 2002

Electronic boards of Far-ultraviolet IMaging Spectrograph (FIMS) should be designed to maintain their performances, and their temperatures should be remained within the allowed temperatures in operational environments. Thermal analysis at the electronic board level has been performed, and it is confirmed the electronics parts could be kept within their allowed temperature ranges.

• Journal of The Korean Astronomical Society
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• v.54 no.5
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• pp.139-155
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• 2021

We present an updated version of the multilayer spectral inversion (MLSI) recently proposed as a technique to infer the physical parameters of plasmas in the solar chromosphere from a strong absorption line. In the original MLSI, the absorption profile was constant over each layer of the chromosphere, whereas the source function was allowed to vary with optical depth. In our updated MLSI, the absorption profile is allowed to vary with optical depth in each layer and kept continuous at the interface of two adjacent layers. We also propose a new set of physical requirements for the parameters useful in the constrained model fitting. We apply this updated MLSI to two sets of Hα and Ca II line spectral data taken by the Fast Imaging Solar Spectrograph (FISS) from a quiet region and an active region, respectively. We find that the new version of the MLSI satisfactorily fits most of the observed line profiles of various features, including a network feature, an internetwork feature, a mottle feature in a quiet region, and a plage feature, a superpenumbral fibril, an umbral feature, and a fast downflow feature in an active region. The MLSI can also yield physically reasonable estimates of hydrogen temperature and nonthermal speed as well as Doppler velocities at different atmospheric levels. We conclude that the MLSI is a very useful tool to analyze the Hα line and the Ca II 8542 line spectral daya, and will promote the investigation of physical processes occurring in the solar photosphere and chromosphere.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.38.4-39
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• 2021

The Local Volume Mapper (LVM), for the Sloan Digital Sky Survey V, consists of four 16 cm telescopes with three fiber spectrographs in the Las Campanas Observatory in Chile. With the fixed telescopes on optical tables, the Alt-Alt mounted siderostats point and guide targets during spectrograph exposures. We are developing the integrated LVM instrument control software. Considering international travel restrictions caused by the COVID-19 pandemic in 2021, we decided to make a simplified version of siderostat to test the LVM telescope control system in Korea. The prototype siderostat consists of two aluminum flat mirrors, optomechanical housing structures made by aluminum profiles, and the Planewave L-350 mount. We designed the optical mirrors and the optomechanical structure of the siderostat. From structural analysis at various pointing cases, we estimated the tilt misalignments of mirrors within 4 arcsec, which would affect the telescope pointing errors.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.46.3-47
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• 2021

Recently a multilayer spectral inversion (MLSI) model has been proposed to infer the physical parameters of plasmas in the solar chromosphere. The inversion solves a three-layer radiative transfer model using the strong absorption line profiles, H alpha and Ca II 8542 Å, taken by the Fast Imaging Solar Spectrograph (FISS). The model successfully provides the physical plasma parameters, such as source functions, Doppler velocities, and Doppler widths in the layers of the photosphere to the chromosphere. However, it is quite expensive to apply the MLSI to a huge number of line profiles. For example, the calculating time is an hour to several hours depending on the size of the scan raster. We apply deep neural network (DNN) to the inversion code to reduce the cost of calculating the physical parameters. We train the models using pairs of absorption line profiles from FISS and their 13 physical parameters (source functions, Doppler velocities, Doppler widths in the chromosphere, and the pre-determined parameters for the photosphere) calculated from the spectral inversion code for 49 scan rasters (~2,000,000 dataset) including quiet and active regions. We use fully connected dense layers for training the model. In addition, we utilize a skip connection to avoid a problem of vanishing gradients. We evaluate the model by comparing the pairs of absorption line profiles and their inverted physical parameters from other quiet and active regions. Our result shows that the deep learning model successfully reproduces physical parameter maps of a scan raster observation per second within 15% of mean absolute percentage error and the mean squared error of 0.3 to 0.003 depending on the parameters. Taking this advantage of high performance of the deep learning model, we plan to provide the physical parameter maps from the FISS observations to understand the chromospheric plasma conditions in various solar features.