• 천문학회보
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• 제35권2호
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• pp.41.1-41.1
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• 2010

It has been suggested that merging plays an important role in the formation and the evolution of early-type galaxies. Optical-NIR color gradients of early-type galaxies in high density environments are found to be less steep than those in low density environment, hinting frequent merger activities in early-type galaxies in high density environment. In order to confirm if the flat color gradient is the result of dry merger, we decided to look deeply to find merging features and get their relation with color gradient. We selected samples which show extreme values of optical-NIR color gradients based on the data of previous study, and observed them at Maidanak observatory 1.5m telescope with long exposure. After masking out overlaid sources, our analysis reveals that these galaxies do not have extreme color gradient values. High degree sky flat technique was used during observation to aid discovery of faint, extended features. However, flatness of detector (SNUCAM) was good enough, so we could not see any marked improvement in image quality compared to those using normal sky flats. Additionally we noticed a feature that looks like merging tidal tail in the CFHT archival image, but this does not show up on the image we obtained. This demonstrates that flatness and correct sky estimation is very important when we look for faint merging features. In future we plan to enlarge the number of the sample.

• 천문학회보
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• 제35권2호
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• pp.82.1-82.1
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• 2010

We have investigated the spatial configuration of stars within the tidal radius of metal poor globular cluster NGC 6626 in the bulge direction. Data were obtained in near-IR J,H,Ks bands with wide-field ($20'\times20'$) detector, WIRCam at CFHT. To trace the stellar density around target cluster, we sorted cluster's member stars by using a mask filtering algorithm and weighting the stars on the color-magnitude diagram. From the weighted surface density map, we found that the stellar spatial distributions within the tidal radius appear asymmetric and distorted features. Especially, we found that more prominent over-density features are extending toward the direction of Galactic plane rather than toward the directions of the Galactic center and its orbital motion. This orientation of the stellar density distribution can be interpreted with result of disk-shock effect of the Galaxy that the cluster had been experienced. Indeed, this over-density feature are well represented in the radial surface density profile for different angular sections. As one of the metal poor globular clusters with extended horizontal branch (EHB) in the bulge direction, NGC 6626 is kinematically decoupled from the normal clusters and known to have disk motion of peculiar motion. Thus, our result will be able to add further constraints to understand the origin of this cluster and the formation of bulge region in early universe.

• 천문학회보
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• 제43권1호
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• pp.72.2-72.2
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• 2018

The Opposition Effect (OE) is an enhancement of the brightness of a reflecting light as the phase angle (the Sun-target-observer angle) approaches zero. The mechanisms have been studied both theoretically and experimentally and nowadays recognized that there are two major mechanisms, namely, coherent backscattering OE (CBOE) and shadow hiding OE (SHOE). From data analyses of an S-type asteroid Itokawa taken with the Hayabusa spacecraft onboard camera, it is suggested that the CBOE would be dominant at phase angle smaller than ~ 1.4 deg, while SHOE dominates at larger phase angles (M. Lee & M. Ishiguro, under review). The study on the physical parameters which affect the OE, such as size and composition, will lead us to find a way to disentangle each of them from observation. The experiments in lab, however, faces two major difficulties: (a) the detector blocks the incident light if phase angle is nearly zero and (b) incident and emission angles must be controlled with high angular resolution to prevent blurring of OEs at different phase angles in one measurement. In this presentation, we introduce a new apparatus which has been installed at Seoul National University to investigate the OE in our lab, and summarize the initial results. It will be a valuable starting point to establish infrastructure in Korea, and will shed light on the investigation of OE physics using laboratory simulants.

• 천문학회보
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• 제36권2호
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• pp.128.2-128.2
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• 2011

Experiments to study high-energy cosmic rays (CRs) employ Monte Carlo codes for extensive air shower (EAS) simulations to figure out the properties of CRs. COSMOS and CORSIKA among EAS simulation codes are currently being used to analyze the data of the Telescope Array experiment. We have generated a library of about 10,000 simulated EASs with the primary energy ranging from $10^{18.5}eV$ to $10^{20}eV$ and the zenith angle of primary particles ranging from 0 to 45 degree for proton and iron primaries. We have compared the results predicted by CORSIKA and COSMOS under the same condition. In this talk, we show the differences in the energy spectra at the ground, the longitudinal shower profile as a function of atmospheric depth, the Calorimetric energy, and the Xmax distribution. We also discuss the lateral distribution function obtained from GEANT4 simulations which is being used to measure the detector response.

• 천문학회보
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• 제36권2호
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• pp.94.2-94.2
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• 2011

Electron microbursts, energetic electron precipitation having duration less than 1 sec, have been thought to be generated by chorus wave and electron interactions. While the coincidence of chorus and microburst occurrence supports the wave-particle interaction theory, more crucial evidences have not been observed to explain the origin of microbursts. We propose the measurement of energy dispersion of microbursts could be an evidence supporting wave-particle theory. During chorus waves propagate along magnetic field, the resonance condition should be satisfied at different magnetic latitude for different energy electrons. If we observed electron microbursts at low altitude, the arrival time of different energy electrons should make unique dispersion structures. In order to observe such energy dispersion, we need a detector having fast time resolution and wide energy range. Our study is motivated from defining the time resolution and energy range of the detectors required to measure microburst energy dispersions. We performed test particles simulation to investigate how electrons interact with simple coherent waves like chorus waves. We compute a large number of electron's trajectories and successfully produce energy dispersion structures expected when microbursts are observed with 10 msec time resolution detectors at the altitude of 600 km. These results provide useful information in designing electron detectors for the future mission.

• 천문학논총
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• 제30권2호
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• pp.251-254
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• 2015

Low resolution spectra of Nova Delphini 2013 (V339 Del) in the optical range have been obtained at Bosscha Observatory, Indonesia during its maximum light (V = 4.3). Spectra were observed from August 16 to 27, 2013. The GAO-ITB RTS 20.3 cm telescope, and SBIG DSS-7 spectrograph and SBIG ST-7 XE as the detector have been employed throughout the observations. The spectra show P-Cygni profiles in Balmer, NaI'D' and Fe II lines, from which we determined shell expansion velocities of $1421.66{\pm}39.18km/s$, $1227.54{\pm}21.57km/s$ and 1402.86 km/s, respectively. Our spectroscopic observations followed the spectral evolution of V339 Del from the pre-maximum phase to early Orion phase. The characteristics of the nova Delphini 2013 resembles those of Fe II-type novae.

• 천문학회보
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• 제37권2호
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• pp.222.1-222.1
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• 2012

JEM-EUSO (Extreme Universe Space Observatory on-board the Japanese Experiment Module)는 국제우주정거장(International Space Station)의 일본 실험 모듈인 'KIBO'에 우주 망원경을 설치하여, 100 EeV이상의 초고에너지 우주선 관측을 수행함으로써, 초고에너지의 스펙트럼, 구성성분과 기원을 연구하는 국제공동연구 프로젝트이다. 구경 2.5 m로 60도의 광시야각을 가지는 대형 굴절 망원경을 통해서, 지구 대기에 우주선 shower로부터 발생한 형광 신호를 관측하려고 한다. 이 프로젝트는 2016~2017년에 발사되어, 5년 이상의 임무 수행을 목표로 하고 있으며, 그 전단계로 Prototype 시스템을 가지고 지상실험인 EUSO-TA와 고도 40 km에서 수행할 EUSO-Balloon실험을 준비하고 있다. 먼저, 망원경의 prototype을 2012년 12월쯤 미국 유타에 있는 Telescope Array(TA) 실험에 설치하여 우주선 또는 임의로 인가한 광원에 의해서 생성된 shower를 TA의 Fluorescence Detector와 함께 측정하여, 시스템 calibration과 더불어 지상에 검출된 우주선을 연구할 계획이다. 그 이듬해인 2013년 여름에는 Balloon에 망원경의 Engineering model을 실어서, 대기고도 40 km아래에서 우주선에 의해 생성되는 shower를 개발한 트리거 시스템을 통해서 검출하고, 대기권에 존재하는 UV background 광원들을 측정하여 우주선을 연구할 예정이다. 한국 그룹은 JEM-EUSO을 위해서 개발한 디지털 신호처리 및 트리거 장치의 제작 중에 있으며, 위의 실험들을 위해 망원경과 함께 조립하여 테스트를 수행할 계획이다.

• 천문학회보
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• 제46권1호
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• pp.37.1-37.1
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• 2021

For the first time in Korea, we are developing technology for gravitational wave (GW) detectors as a major R&D program. Our main research target is quantum noise reduction technology which can enhance the sensitivity of a GW detector beyond its limit by classical physics. Technology of generating squeezed vacuum state of light (SQZ) can suppress quantum noise (shot noise at higher frequencies and radiation pressure noise at lower frequencies) of laser interferometer type GW detectors. Squeezing technology has recently started being used for GW detectors and becoming necessary and key components. Our ultimate goal is to participate and make contribution to international collaborations for upgrade of existing GW detectors and construction of next generation GW detectors. This presentation will summarize our results in 2020 and plan for the upcoming years. Technical details will be presented in other family talks.

• 천문학회보
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• 제46권1호
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• pp.44.1-44.1
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• 2021

한기로 나누어 보면, 흑점의 관측 빈도는 두 기간에서 비슷하지만, 오로라는 냉한기에 집중적으로 관측된다. 특이하게도, 크기가 큰 흑점의 경우는 냉한기보다 온난기에서 관측 빈도가 세 배 이상 높다. 또한, 흑점과 관련된 오로라의 강도를 분석해보면 크기가 큰 흑점은 작은 흑점보다 2~3배 이상 지구영향성이 높다는 것을 알 수 있다.

• 천문학회보
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• 제46권1호
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• pp.37.3-38
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• 2021

Radiation pressure noise of photon and photon shot noise are quantum noise limitation in interferometric gravita-tional wave detectors. Since relationship between the two noises is position and momentum of the Heisenberg uncertainty principle, quantum non-demolition (QND) technique is required to reduce the two noises at the same time. Frequency dependent squeezing using a filter cavity is one of realistic solutions for QND measurement and experimental results show that its cutting-edge performance is sufficient to apply to the current gravitational wave detectors. A 300m filter cavity is under construction at adv-LIGO. KAGRA (gravitational wave detector in Japan) has also started international collaboration to build a filter cavity. Recently we joined the filter cavity project for KAGRA. Current status of squeezing and filter cavity research at KASI and details of the KAGRA filter cavity project will be presented.