• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.31.1-31.1
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• 2010

We present a spectroscopic study of the globular clusters (GCs) in the giant elliptical galaxy (gE) NGC 4636 in the Virgo cluster. Line indices of GCs in NGC 4636 are measured from the integrated spectra obtained with Faint Object Camera and Spectrograph (FOCAS) on the Subaru Telescope. We derive the [Fe/H] of the GCs in NGC 4636 using Brodie & Huchra (1990) method. The [Z/H], age, and alpha-element of the GCs are obtained from the comparison of the Lick line indices with the SSP model grid. We investigate the distribution and radial variation of the metallicity, age, and alpha-element of NGC 4636 GCs. The metallicity distribution of NGC 4636 GCs shows a bimodality. The chemical properties of these GCs show little radial variation. These results will be discussed with regard to the formation and evolution of NGC 4636.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.69.2-69.2
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• 2010

The far-ultraviolet (FUV) H2 and C IV emission images and spectra of Orion Eridanus Superbubble (OES) is hereby presented. The OES seems to consists of multiple phase through the detection of highly-ionized gas and pervasive neutral hydrogen. The former is traced by hot gas while the latter is traced by cold medium. A spectral image made with H2 fluorescent emission shows that the spatial distribution of hydrogen molecule is well correlated with the dust map. The model spectra was taken from a photodissociation region (PDR) radiation code which find a best suitable parameter such as hydrogen density, gas temperature and incident uv intensity of the radiation field. C IV emission is caused by intermediate temperature ISM about 10^4.5 K~10^6 K. Therefore we could get more clear evidence to reveal the structure of OES. Feature of spectra for the each sub region is also presented and discussed. The data were obtained with the Far-Ultraviolet Imaging Spectrograph (FIMS) and the whole data handling were followed by previous FIMS analysis.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.60.2-60.2
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• 2010

We have studied the abundance ratio of HNC and HCN toward the Red MSX Sources (RMS) using HCN (J=1-0), HNC (J=1-0), $H^{13}CN$ (J=1-0), $HN^{13}C$ (J=1-0),and $N_2H^+$ (J=1-0) lines observed with the Mopra 22 m radio telescope. The RMS are massive young stellar objects identified by the MSX satellite data combined with the 2MASS data. HCN and HNC (a geometrical isomer of HCN) are among the most basic interstellar molecules. According to our analysis, the column density of HCN is found to be correlated with that of HNC. Additionally, the [HNC]/[HCN] abundance ratio is sensitive to the core temperature because HNC is depleted in high temperature regions. This result is consistent with the previous results seen in low mass starless or protostellar cores.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.71.1-71.1
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• 2010

The far-ultraviolet (FUV) C IV and H2 emission spectra of Orion-Eridanus Superbubble (OES) is hereby presented. The OES seems to consist of multiple phase through the detection of highly-ionized gas and pervasive neutral hydrogen. The former is traced by hot gas while the latter is traced by cold medium. A spectral image made with H2 fluorescent emission shows that the spatial distribution of hydrogen molecule is well correlated with the dust map. The model spectra was taken from a photodissociation region (PDR) radiation code which finds a best suitable parameter such as hydrogen density and intensity of the radiation field. C IV emission is caused by intermediate temperature ISM about 10^5 K. Therefore we could get more clear evidence to reveal the morphology of OES. In this process, the hydrogen density and gas temperature were also estimated. The data were obtained with the Far-Ultraviolet Imaging Spectrograph (FIMS) and the whole data handling were followed by previous FIMS analysis.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.55.2-55.2
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• 2017

We study the effect of driving scheme on the density-magnetic field correlation. We numerically investigate how the correlation time of driving affects the correlation between density and magnetic field. We performed MHD turbulence simulation using two different driving schemes - a finite-correlated driving and a delta-correlated driving. In the former, the forcing vectors change continuously with a correlation time comparable to the large-eddy turnover time. In the latter, the direction and amplitude of driving changes in a very short time scale.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.30.1-30.1
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• 2017

In the hope to detect low-surface brightness features (${\mu}_{r^{\prime}}{\sim}27\;mag\;arcsec^{-2}$), we carried out KASI-Yonsei Deep Imaging Survey for Clusters (KYDISC) targeting 14 local clusters at 0.016 < z < 0.145 using Magellan/IMACS telescope and CFHT/MegaCam. Out of 1450 cluster galaxies, 18% of galaxies show the signatures of galaxy mergers. We explore merger-driven changes from various point-of-view. We first examine color-magnitude relations, and find that galaxies related to recent mergers are populated more on blue color than their counterparts. Besides, we find the extremely low frequency of mergers on low-mass red-sequence galaxies, suggesting a migration of red galaxies into the green-valley region through merger-driven star-formation. We also study the mass-size relation of our sample, finding a larger galaxy size in galaxies related to recent mergers. Our results suggest that mergers can simultaneously change properties of galaxies, making outliers on galactic scaling relations.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.36.2-36.2
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• 2017

Massive stars (${\geq}8M_{\odot}$) are believed to experience core-collapse and finish their lives as supernova (SN) explosions. Astronomers operating the current SN survey facilities try to catch the first moments of SN explosions. Since neutrinos are emitted first from the SNe before the electromagnetic lights, any neutrino detections from more than two sites within around 10 seconds could be useful alert for early follow-up observations, especially for optical SN follow-up telescopes. In this talk, I will brief the current SN follow-up observation projects, what they want to find out and contribute to SN sciences. Focus will be on the early detection and early sciences on SNe, which is what the Korean Neutrino Telescope can contribute most importantly.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.70.2-70.2
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• 2018

KMTNet에서는 프로젝트의 소개와 운영현황 등 파악하기 위해 웹서비스를 운영하고 있다. 홈페이지(http://kmtnet.kasi.re.kr; 국문, 영문)에는 최신 뉴스와 공지사항, 실시간 모니터링 영상 및 기상정보, 관측일정, 관측자료 공개, 활용성과 등을 게시 하였고, 관측 결과와 운영 정보 관리를 위해서 모니터링 홈페이지(kmtnet-monitor)를 제작하였다. KMTNet은 남반구 3개 관측소에 상주하는 현지 관측자에 의해 관측이 이루어지기 때문에, 국내 연구자가 남반구 관측소 현황을 파악할 수 있는 모니터링 시스템이 필수적이다. 웹서비스에 실시간 기상과 관측자료 전송속도를 함께 표시하여 관측 진행 여부를 확인할 수 있으며, 관측일지를 데이터베이스화하여 망원경/카메라/관측돔의 이상 유무, 관측 현황, 기상/시상 통계 등으로 활용하고 있다. 여기서는 지금까지 개발한 웹 서비스를 소개하고 앞으로 관측소 운영에 유용한 정보와 웹 서비스의 발전 방향에 대해 논의하고자 한다.

• Korean Journal of Remote Sensing
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• v.31 no.4
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• pp.331-336
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• 2015

In this study, a numerical model developed for sunshine duration based on GIS data was used. This model considers blocking caused by topography and buildings and it is properly applicable to evaluation of sunshine duration environment in urban areas. The model reasonably well predicted the solar altitude and azimuth angels, compared to those provided by Korea Astronomy and Space Science Institute (KASI). The developed model was applied to evaluation of sunshine duration environment around the Seonleung Park located near a building-congested area in Seoul. The model well reproduced shadow caused by buildings and/or topography in the numerical domain at 09:00 on August 1, 2015. In addition, the model was applied to finding a suitable measurement sites for pyrheliometer around the Seonleung Park. The model was also usefully applied to finding a suitable site for pyrheliometer in an urban area.

• International Journal of Aeronautical and Space Sciences
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• v.6 no.2
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• pp.56-63
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• 2005

Some methods have been presented to avoid collisions among satellites for satellite formation flying mission. The potential function method based on Lyapunov's theory is known as a powerful tool for collision avoidance in the robotic system because of its robustness and flexibility. During the last decade, a potential function has also been applied to UAV's and spacecraft operations, which consists of repulsive and attractive potential. In this study, the controller is designed using a potential function via sliding mode technique for the configuration of satellite formation flying. The strategy is based on enforcing the satellite to move along the gradient of a given potential function. The new scalar velocity function is introduced such that all satellites reach the goal points simultaneously. Simulation results show that the controller drives the satellite toward the desired point along the gradient of the potential function and is robust against external disturbances.