• Journal of Astronomy and Space Sciences
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• 제29권2호
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• pp.233-244
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• 2012

The Korea Astronomy and Space Science Institute and the Department of Astronomy at the University of Texas at Austin are developing a near infrared wide-band high resolution spectrograph, immersion grating infrared spectrometer (IGRINS). The compact white-pupil design of the instrument optics uses seven cryogenic mirrors, including three aspherical off-axis collimators and four flat fold mirrors. In this study, we introduce the optomechanical mount designs of three off-axis collimating mirrors and one flat slit-viewer fold mirror. Two of the off-axis collimators are serving as H and K-band pupil transfer mirrors, and are designed as system alignment compensators in combination with the H2RG focal plane array detectors in each channel. For this reason, the mount designs include tip-tilt and parallel translation adjustment mechanisms to properly perform the precision alignment function. This means that the off-axis mirrors' optomechanical mount designs are among the most sensitive tasks in all IGRINS system hardware. The other flat fold mirror is designed within its very limitedly allowed work space. This slit-viewer fold mirror is mounted with its own version of the six-point kinematic optics mount. The design work consists of a computer-aided 3D modeling and finite element analysis (FEA) technique to optimize the structural stability and the thermal behavior of the mount models. From the structural and thermal FEA studies, we conclude that the four IGRINS mirror mounts are well designed to meet all optical stability tolerances and system thermal requirements.

• 천문학논총
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• 제30권2호
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• pp.665-669
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• 2015

The Kepler mission has shown that small planets are extremely common. It is likely that nearly every star in the sky hosts at least one rocky planet. We just need to look hard enough-but this requires vast amounts of telescope time. MINERVA (MINiature Exoplanet Radial Velocity Array) is a dedicated exoplanet observatory with the primary goal of discovering rocky, Earth-like planets orbiting in the habitable zone of bright, nearby stars. The MINERVA team is a collaboration among UNSW Australia, Harvard-Smithsonian Center for Astrophysics, Penn State University, University of Montana, and the California Institute of Technology. The four-telescope MINERVA array will be sited at the F.L. Whipple Observatory on Mt Hopkins in Arizona, USA. Full science operations will begin in mid-2015 with all four telescopes and a stabilised spectrograph capable of high-precision Doppler velocity measurements. We will observe ~100 of the nearest, brightest, Sun-like stars every night for at least five years. Detailed simulations of the target list and survey strategy lead us to expect $15{\pm}4$ new low-mass planets.

• 천문학회보
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• 제37권2호
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• pp.113.1-113.1
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• 2012

The characteristics of Doppler shifts in a quiet region of the Sun are investigated by comparing between the $H{\alpha}$ line and the Caii infrared line at 854.2 nm. A small area of $16^{\prime\prime}{\times}40^{\prime\prime}$ was observed for about half an hour with the Fast Imaging Solar Spectrograph (FISS) of the 1.6 meter New Solar Telescope (NST) at Big Bear Solar Observatory. The observed area contains a network region and an internetwork region, and identified in the network region are $H{\alpha}$ fibrils, Caii fibrils and bright points. We infer the Doppler velocity from each line profile at a point with the lambdameter method as a function of half wavelength separation ${\Delta}{\lambda}$. It is confirmed that the bisector of the spatially-averaged Caii line profile has an inverse C-shape of with a significant peak redshift of +1.8 km/s. In contrast, the bisector of the spatially-averaged $H{\alpha}$ line profile has a different shape; it is almost vertically straight or, if not, has a C-shape with a small peak blueshift of -0.5 km/s. In both the lines, the bisectors of bright network points are much different from those of other features in that they are significantly redshifted not only at the line centers, but also at the wings. We also find that the spatio-temporal fluctuation of Doppler shift inferred from the Caii line is correlated with those of the $H{\alpha}$ line. The strongest correlation occurs in the internework region, and when the inner wings rather than the line centers are used to determine Doppler shift. In this region, the RMS value of Doppler shift fluctuation is the largest at the line center, and monotonically decreases with ${\Delta}{\lambda}$. We discuss the physical implications of our results on the formation of the $H{\alpha}$ line and Caii 854.2 nm line in the quiet region chromosphere.

• 천문학회보
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• 제36권1호
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• pp.37.2-37.2
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• 2011

Our previous study on tiny pores (R < 2") observed by HINODE/Solar Optical Telescope (SOT) revealed that the plasma in the pores at the photosphere is always moving down and the pores are surrounded by the strong downward motions (highly red-shifted) of neighboring granulations. From this study, we speculated that the flow motions above the pore should be related with the motions at the photosphere, since the pore is strong magnetic field region. Meanwhile, SNU and KASI installed Fast Imaging Solar Spectrograph (FISS) in the Cude room of the 1.6 m New Solar Telescope (NST) at Big Bear Solar Observatory. FISS is a unique system that can do imaging of H-alpha and Ca II 8542 band simultaneously, which is quite suitable for studying of dynamics of chromosphere. To get some clue on the relationship between the photospheric and low-chromospheric motions at the pore region, we took a coordinate observation with NST/FISS and Hinode/SOT for new emerging active region (AR11117) on October 26, 2010. In the observed region, we could find two tiny pores and two small magnetic islands (SMIs), which have similar magnetic flux with the pores but does not look dark. Magnetic flux density and Doppler velocities at the photosphere are estimated by applying the center-of-gravity (COG) method to the HINODE/spectropolarimeter (SP) data. The line-of-sight motions above the photosphere are determined by adopting the bisector method to the wing spectra of Ha and CaII 8542 lines. As results, we found the followings. (1) There are upflow motion on the pores and downflow motion on the SMIs. (2) Towards the CaII 8542 line center, upflow motion decrease and turn to downward motion in pores, while the speed of down flow motion increases in the SMIs. (3) There is oscillating motion above pores and the SMIs, and this motion keep its pattern along the height. (4) As height increase, there is a general tendency of the speed shift to downward on pores and the SMIs. This is more clearly seen on the other regions of stronger magnetic field. In this talk, we will present preliminary understanding of the coupling of pore dynamics between the photosphere and the low-chromosphere.

• 한국광학회지
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• 제28권3호
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• pp.116-121
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• 2017

본 연구에서는 오염된 지표면의 화학물질을 탐지하기 위해 라만 라이다 기반의 지표면 화학물질 탐지 시스템을 설계하고 제작하였다. 화학물질에 레이저를 조사하였을 때 나오는 라만 산란광을 측정하여 측정 시료의 분광정보를 얻는 라만 라이다 시스템은 측정 시료의 라만 산란광을 유도하는 레이저를 포함한 송광부와 라만 산란광을 수광하는 수광부, 수광된 광을 파장별로 나눠주는 분광부로 구성된다. 측정거리가 변하여도 수광부에 의해 집광되는 광이 동일한 위치에 집속되도록 code V 시뮬레이터를 사용하여 광학계를 설계하였다. 총 12종의 화학물질이 유리와 콘크리트 위에 있을 때 라만 스펙트럼을 측정하여 비교한 결과 라만 스펙트럼의 특성이 유사하지만, 세기에 차이가 있는 것을 관찰하였다. 고체 시료인 PTFE (polytetra-fluoroethylene)를 사용하여 시스템과의 거리 변화에 따른 라만 스펙트럼의 세기를 비교한 결과 시뮬레이션에서 얻은 거리에 따른 수광 효율과 유사한 것을 확인하였다. 결론적으로 본 시스템을 이용하여 다양한 거리에서도 화학물질의 라만 스펙트럼 측정이 가능함을 확인하였다.

• 한국광학회지
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• 제33권5호
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• pp.201-209
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• 2022

기존 마이크로스폿 분광타원계의 집속광학계를 개선하여 원자힘 현미경(atomic force microscope, AFM) 헤드를 장착할 수 있도록 한 AFM 융합형 마이크로스폿 분광타원계를 개발하였다. 빔의 워블에 의한 영향을 최소화하기 위해 편광자-시료-보정기-검광자 배치에서 회전보정기 구동방식을 채택하고 이상적인 4분파장 위상지연 특성으로부터 벗어나는 비색성 위상지연자를 사용할 수 있도록 측정이론을 제시하였다. 개발된 마이크로스폿 분광타원계는 AFM 헤드를 장착한 상태에서도 20 ㎛ 이하의 스폿 사이즈를 가지며 190-850 nm의 파장대역에 걸쳐 구동하고 δΔ ≤ 0.05°와 δΨ ≤ 0.02°의 측정정밀도를 가지는 것을 확인하였다. 연속회전하는 스테핑 모터의 속도와 분광계를 정밀하게 동기화시켜 ≤3 s/sp의 빠른 측정속도를 구현하였다. AFM과 융합된 마이크로스폿 분광타원계는 초미세 패턴시료의 구조 및 광학물성 분석에 유용하게 사용될 수 있을 것으로 기대한다.

• 천문학회지
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• 제56권2호
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• pp.213-224
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• 2023

Type II solar radio bursts show frequency drifts from high to low over time. They have been known as a signature of coronal shock associated with Coronal Mass Ejections (CMEs) and/or flares, which cause an abrupt change in the space environment near the Earth (space weather). Therefore, early detection of type II bursts is important for forecasting of space weather. In this study, we develop a deep-learning (DL) model for the automatic detection of type II bursts. For this purpose, we adopted a 1-D Convolution Neutral Network (CNN) as it is well-suited for processing spatiotemporal information within the applied data set. We utilized a total of 286 radio burst spectrum images obtained by Hiraiso Radio Spectrograph (HiRAS) from 1991 and 2012, along with 231 spectrum images without the bursts from 2009 to 2015, to recognizes type II bursts. The burst types were labeled manually according to their spectra features in an answer table. Subsequently, we applied the 1-D CNN technique to the spectrum images using two filter windows with different size along time axis. To develop the DL model, we randomly selected 412 spectrum images (80%) for training and validation. The train history shows that both train and validation losses drop rapidly, while train and validation accuracies increased within approximately 100 epoches. For evaluation of the model's performance, we used 105 test images (20%) and employed a contingence table. It is found that false alarm ratio (FAR) and critical success index (CSI) were 0.14 and 0.83, respectively. Furthermore, we confirmed above result by adopting five-fold cross-validation method, in which we re-sampled five groups randomly. The estimated mean FAR and CSI of the five groups were 0.05 and 0.87, respectively. For experimental purposes, we applied our proposed model to 85 HiRAS type II radio bursts listed in the NGDC catalogue from 2009 to 2016 and 184 quiet (no bursts) spectrum images before and after the type II bursts. As a result, our model successfully detected 79 events (93%) of type II events. This results demonstrates, for the first time, that the 1-D CNN algorithm is useful for detecting type II bursts.

• 천문학회지
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• 제56권2호
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• pp.169-185
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• 2023

The GMT-Consortium Large Earth Finder (G-CLEF) is the first instrument for the Giant Magellan Telescope (GMT). G-CLEF is a fiber feed, optical band echelle spectrograph that is capable of extremely precise radial velocity measurement. G-CLEF Flexure Control Camera (FCC) is included as a part in G-CLEF Front End Assembly (GCFEA), which monitors the field images focused on a fiber mirror to control the flexure and the focus errors within GCFEA. FCC consists of an optical bench on which five optical components are installed. The order of the optical train is: a collimator, neutral density filters, a focus analyzer, a reimager and a detector (Andor iKon-L 936 CCD camera). The collimator consists of a triplet lens and receives the beam reflected by a fiber mirror. The neutral density filters make it possible a broad range star brightness as a target or a guide. The focus analyzer is used to measure a focus offset. The reimager focuses the beam from the collimator onto the CCD detector focal plane. The detector module includes a linear translator and a field de-rotator. We performed thermoelastic stress analysis for lenses and their mounts to confirm the physical safety of the lens materials. We also conducted the global structure analysis for various gravitational orientations to verify the image stability requirement during the operation of the telescope and the instrument. In this article, we present the opto-mechanical detailed design of G-CLEF FCC and describe the consequence of the numerical finite element analyses for the design.

• 한국화재소방학회논문지
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• 제26권6호
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• pp.99-108
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• 2012

본 연구에서는 최근 빈번히 발생하고 있는 폐타이어의 가공 및 저장상황에서의 산화열에 의한 자연발화현상을 규명하기 위해 폐타이어 분쇄물에 대한 화재 재연실험과 가공 및 저장장소에서 수거한 화재 잔존물에 대한 면밀한 성분 분석 및 발화개시온도, 무게감량, 반응열 등을 분석하였다. 이를 위해 열축적이 용이한 폐타이어 분쇄물 2.5~15 mm 범위의 파쇄된 분쇄물을 대상으로 재연실험 및 DSC 및 TGA, DTA, DTG, GC/MS를 통한 열분석을 시행하여 자연발화의 가능성에 대한 과학적인 개연성을 부여하고자 하였다. 연구결과를 살펴보면 재연실험을 통하여 관찰한 결과 48시간 저장시에 온도의 급상승($178^{\circ}C$) 및 탄화현상, 연기발생이 관찰되었다. 또한 DTA, DTG 분석한 결과 $166.15^{\circ}C$에서 최초 중량감소가 일어나는 것으로 분석되었다. 아울러 DSC 및 TGA를 이용한 폐타이어 분쇄물 1(Unburnt)의 실험결과 $180^{\circ}C$ 부근에서 열분해를 시작하는 것으로 나타나 폐타이어의 발화 개시온도는 $160{\sim}180^{\circ}C$라고 말할 수 있다. 그리고 $305^{\circ}C$에서 최초 원료 무게의 10 % 중량감소가 있었고, 원료 무게의 50 % 중량감소는 $416^{\circ}C$로 분석되었다. 또한 GC/MS와 DSC를 이용한 산화성 및 자기반응성시험에 있어서는 1,3 cyclopentnadiene 등 산화성성분이 다량 검출되었지만 표준물질과 폐타이어 분쇄물과의 열분석실험결과 기준치 이하로 분석되어 자기반응성은 없는 것으로 분석되었다. 따라서 폐타이어의 산화열에 의한 자연발화현상을 방지하기 위해서는 분쇄시 열축적이 적거나 없는 냉동파쇄방식 등의 가공공정으로 전환유도를 고려해야하며 현재 파쇄 분쇄물을 대형 마대(500 kg)로 저장하는 방식에서, 마대를 소형화하여 분쇄물을 분산 저장하는 등의 방법으로 열축적을 방지해야한다.

• 천문학회보
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• 제45권1호
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• pp.34.3-34.3
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• 2020

Faint z ~ 5 quasars with M1450 ~ -23 mag are known to be the potentially important contributors to the ultraviolet ionizing background in the post-reionization era. However, their number density has not been well determined, making it difficult to assess their role in the early ionization of the intergalactic medium (IGM). In this work, we present the updated results of our z ~ 5 quasar survey using the Infrared Medium-deep Survey (IMS), a near-infrared imaging survey covering an area of 85 square degrees. From our spectroscopic observations with the Gemini Multi-Object Spectrograph (GMOS) on the Gemini-South 8 m Telescope, we discovered eight new quasars at z ~ 5 with -26.1 ≤ M1450 ≤ -23.3. Combining our IMS faint quasars with the brighter Sloan Digital Sky Survey (SDSS) quasars, we derive, for the first time, the z ~ 5 quasar luminosity function (QLF) without any fixed parameters down to the magnitude limit of M1450 = -23 mag. We find that the faint-end slope of the QLF is very flat (-1.2) with a characteristic luminosity of -25.7 mag. The number density of z ~ 5 quasars from the QLF gives lower ionizing emissivity and ionizing photon density than those in previous works. These results imply that quasars are responsible for only 10-20% of the photons required to completely ionize the IGM at z ~ 5, disfavoring the idea that quasars alone could have ionized the IGM at z ~ 5.