본문 바로가기 메뉴바로가기
Total 16   
16
  • Kyungsuk Cho
  • Hongyu Liu
  • Hongyu Liu, Yao Chen, Kyungsuk Cho, Shiwei Feng, Veluchamy Vasanth, Artem Koval, Guohui Du, Zhao Wu, Chuanyang Li
  • 2018
  • Solar Physics, 293, 58
 A stationary Type IV (IVs) radio burst was observed on September 24, 2011. Observations from the Nançay RadioHeliograph (NRH) show that the brightness temperature (  TB ) of this burst is extremely high, over   1011  K at 150 MHz and over   108  K in general. The degree of circular polarization (  q ) is between   −60%∼−100% , which means that it is highly left-handed circularly polarized. The flux–frequency spectrum follows a power-law distribution, and the spectral index is considered to be roughly   −3∼−4  throughout the IVs. Radio sources of this event are located in the wake of the coronal mass ejection and are spatially dispersed. They line up to present a formation in which lower-frequency sources are higher. Based on these observations, it is suggested that the IVs was generated through electron cyclotron maser emission.
15
OWL-Net: A global network of robotic telescopes for satellite observation
  • Jung Hyun Jo
  • Jin Choi
  • Jang-Hyun Park, Hong-Suh Yim, Young-Jun Choi, Jung Hyun Jo, Hong-Kyu Moon, Young-Sik Park, Young-Ho Bae, Sun-Youp Park, Dong-Goo Roh, Sungki Cho, Eun-Jung Choi, Myung-Jin Kim, Jin Choi
  • 2018
 The OWL-Net (Optical Wide-field patroL Network) is composed of 0.5-m wide-field optical telescopes spread over the globe (Mongolia, Morocco, Israel, South Korea, and USA). All the observing stations are identical, operated in a fully robotic manner, and controlled by the headquarters located in Daejeon, Korea. The main objective of the OWL-Net is to obtain the orbital information of Korean LEO and GEO satellites using purely optical means and to maintain their orbital elements. The aperture size of the mirror is 0.5?m in the Ritchey-Chretien configuration, and its field of view is 1.1?deg on the CCD sensor. The telescope is equipped with an electrically cooled 4?K CCD camera with a 9-μm pixel size, and its pixel scale is 1 arcsec/pixel. A chopper wheel with variable speed is adopted to obtain multiple points in a single shot. Each observatory is equipped with a heavy-duty environment monitoring system for robust robotic observation. The headquarters has components for status monitoring, scheduling, network operation, orbit calculation, and database management. The test-phase operation of the whole system began in early 2017, although test runs for individual sites began in 2015. Although the OWL-Net has 7 observation modes for artificial satellites and astronomical objects, we are concentrating on a few modes for LEO satellites and calibration during the early phase. Some early results and analysis for system performance will be presented, and their implications will be discussed.
14
Optical Tracking Data Validation and Orbit Estimation for Sparse Observations of Satellites by the OWL-Net
  • Jung Hyun Jo
  • Jin Choi
  • Jin Choi, Jung Hyun Jo, Hong-Suh Yim, Eun-Jung Choi, Sungki Cho and Jang-Hyun Park
  • 2018
 An Optical Wide-field patroL-Network (OWL-Net) has been developed for maintaining Korean low Earth orbit (LEO) satellites’ orbital ephemeris. The OWL-Net consists of five optical tracking stations. Brightness signals of reflected sunlight of the targets were detected by a charged coupled device (CCD). A chopper system was adopted for fast astrometric data sampling, maximum 50 Hz, within a short observation time. The astrometric accuracy of the optical observation data was validated with precise orbital ephemeris such as Consolidated Prediction File (CPF) data and precise orbit determination result with onboard Global Positioning System (GPS) data from the target satellite. In the optical observation simulation of the OWL-Net for 2017, an average observation span for a single arc of 11 LEO observation targets was about 5 min, while an average optical observation separation time was 5 h. We estimated the position and velocity with an atmospheric drag coefficient of LEO observation targets using a sequential-batch orbit estimation technique after multi-arc batch orbit estimation. Post-fit residuals for the multi-arc batch orbit estimation and sequential-batch orbit estimation were analyzed for the optical measurements and reference orbit (CPF and GPS data). The post-fit residuals with reference show few tens-of-meters errors for in-track direction for multi-arc batch and sequential-batch orbit estimation results.
13
Characteristics of orbit determination with short-arc observation by an optical tracking network, OWL-Net
  • Jung Hyun Jo
  • Jin Choi
  • Jin Choi, Jung Hyun Jo, Kyung-Min Roh, Hong-Suh Yim, Eun-Jung Choi, Sungki Cho
  • 2018
 An optical tracking network, the Optical Wide-field patroL Network (OWL-Net), has been developed to maintain the orbital ephemeris of 11 domestic Low-Earth-orbit satellites. The schedule overlapped events were occurred in the scheduling of the OWL-Net with reducing the optical observation chances. A short-arc observation strategy for the OWL-Net was tested to reduce schedule overlapped events with the optical observation simulation and the orbit determination. In the full-scale optical observation simulation from January 2014 to December 2016, the most frequent overlapped events were occurred 127, 132 and 116 times in the 4th, 34th, and 18th weeks of 2014, 2015, and 2016, respectively. The average number of overlapped event for three years was over 10% for the whole observation chances of five stations. Consequently, the short-arc observation strategy reduced the schedule overlapped events for every observation targets of the OWL-Net. In case of the 5s and 10s cases, the most schedule overlapped events were removed. The test results of the orbit determination results show that the most maximum orbit prediction errors after seven days are maintained at <10 km in the in-track direction for the short-arc observation simulations. The results demonstrate that the short-arc optical observation strategy is more optimal to maintain the accuracy of orbital ephemeris with more observation chances.
12
  • Joon Hyeop Lee
  • Mina Lee, Hye-Ran Oh
  • Lee, Joon Hyeop; Pak, Mina; Lee, Hye-Ran; Oh, Sree
  • 2018
  • ApJ 857 102L
We investigate the properties of bright galaxies of various morphological types in Abell 1139 and Abell 2589, using pixel color–magnitude diagram (pCMD) analysis. The sample contains 32 galaxies brighter than M r  = −21.3 mag with spectroscopic redshifts, which are deeply imaged in the g and rbands using the MegaCam mounted on the Canada–France–Hawaii Telescope. After masking contaminants with two-step procedures, we examine how the detailed properties in the pCMDs depend on galaxy morphology and infrared color. The mean g − r color as a function of surface brightness (μ r ) in the pCMD of a galaxy shows good performance in distinguishing between early- and late-type galaxies, but it is not perfect because of the similarity between elliptical galaxies and bulge-dominated spiral galaxies. On the other hand, the g − r color dispersion as a function of μ r works better. We find that the best set of parameters for galaxy classification is a combination of the minimum color dispersion at μ r  ≤ 21.2 mag arcsec−2 and the maximum color dispersion at 20.0 ≤ μ r  ≤ 21.0 mag arcsec−2; the latter reflects the complexity of stellar populations at the disk component in a typical spiral galaxy. Finally, the color dispersion measurements of an elliptical galaxy appear to be correlated with the Wide-field Infrared Survey Explorer infrared color ([4.6]–[12]). This indicates that the complexity of stellar populations in an elliptical galaxy is related to its recent star formation activities. From this observational evidence, we infer that gas-rich minor mergers or gas interactions may have usually occurred during the recent growth of massive elliptical galaxies.
11
Hybrid modeling of redshift space distortions
  • Yong-Seon Song
  • Minji Oh
  • Song, Yong-Seon; Zheng, Yi; Taruya, Atsushi; Oh, Minji
  • 2018
The observed power spectrum in redshift space appears distorted due to the peculiar motion of galaxies, known as redshift-space distortions (RSD). While all the effects in RSD are accounted for by the simple mapping formula from real to redshift spaces, accurately modeling redshift-space power spectrum is rather difficult due to the non-perturbative properties of the mapping. Still, however, a perturbative treatment may be applied to the power spectrum at large-scales, and on top of a careful modeling of the Finger-of-God effect caused by the small-scale random motion, the redshift-space power spectrum can be expressed as a series of expansion which contains the higher-order correlations of density and velocity fields. In our previous work [JCAP 8 (Aug. 2016) 050], we provide a perturbation-theory inspired model for power spectrum in which the higher-order correlations are evaluated directly from the cosmological N-body simulations. Adopting a simple Gaussian ansatz for Finger-of-God effect, the model is shown to quantitatively describe the simulation results. Here, we further push this approach and present an accurate power spectrum template which can be used to estimate the growth of structure as a key to probe gravity on cosmological scales. Based on the simulations, we first calibrate the uncertainties and systematics in the perturbation theory calculation in a fiducial cosmological model. Then, using the scaling relations, the calibrated power spectrum template is applied to a different cosmological model. We demonstrate that with our new template, the best-fitted growth functions are shown to reproduce the fiducial values in a good accuracy of 1% at k<0.18 Mpc-1 for cosmologies with different Hubble parameters.
10
과학과 기술의 공진화 경영을 통한 거대과학의 추격:천문우주과학과 핵융합연구 사례 비교 (Catch-up in Big Sciences through Co-evolution of Scienceand Technology: The Case of Astronomy and NuclearFusion Research in South Korea)
  • Jeongyoo Hong
  • Syeun Kim
  • 권기석(Kwon, Ki-Seok) , 김시은(Kim, Syeun)
  • 2018
  • 경영교육연구 제33권2호 , 243~257쪽
[연구목적] 본 연구에서는 한국과 같이 과학 추격에 성공하고 있는 국가의 맥락에서, 과학과 기술을 구분하여 양자의 상호작용을 통한 공진화 모델을 제시하였다. 이에 따라 우리나라 천문우주과학과 핵융합연구의 진화 사례를 분석하였다. 이를 통해 국가 및 조직 수준에서 과학의 경영에 대한 시사점을 제공하고자 하였다. [연구방법] 본 연구는 과학의 체제론, 과학과 기술의 상호작용 등에 대한 관련 이론들, 기존에 수행되었던 한국의 기술혁신 연구들과 논의를 검토하여 과학과 기술의 공진화 모델을 도출하였다. 이를 바탕으로 한국의 천문우주과학과 핵융합연구와 관련된 다양한 문헌자료를 수집하고 분석하였다. [연구결과] 과학과 기술의 공진화 모델을 바탕으로 하여, 천문우주과학과 핵융합연구의 발전을 설명하였다. 또한 두 거대과학의 발전과정 동인의 공통점과 차이점을 발견하였다.공통점으로는 정부의 지원사업, 기기 확보와 기술개발의 중요성, 인력의 양성, 해외 협력이 과학과 기술의 상승작용의 토양으로 작용하였다. 한편으로 단계별 진화 및 과학시스템 변화의 동인, 해외 교육훈련의 역할, 과학과 기술의 상호작용의 방향의 비대칭에 있어 차이점을 발견하였다. [연구의 시사점] 국가 과학의 발전에 중요한 역할을 하는 동인으로 정부의 강력한 지원, 첨단 기기의 확보, 연구인력의 팽창, 국내외 기술개발 협력이 중요한 것으로 나타났다. 또한, 과학의 발전을 위한 차별화된 경영이 중요하다는 것을 알 수 있었다. 과학적 역량이 구축되지 않은 단계에서 기술적 돌파구를 이루는 데에는 한계가 있었다. 역으로 기술적 역량은 다음의 과학적 단계로 나아가는 데에 중요하였다.
9
  • Chang Won Lee
  • Shinyoung Kim
  • Tie Liu, Kee-Tae Kim, Mika Juvela, Ke Wang, Ken'ichi Tatematsu, James Di Francesco, Sheng-Yuan Liu, Yuefang Wu, Mark Thompson, Gary Fuller, David Eden, Di Li, I. Ristorcelli, Sung-ju Kang, Yuxin Lin, D. Johnstone, J. H. He, P. M. Koch, Patricio Sanhueza, Sheng-Li Qin, Q. Zhang, N. Hirano, Paul F. Goldsmith, Neal J. Evans II, Glenn J. White, Minho Choi, Chang Won Lee, L. V. Toth, Steve Mairs, H.-W. Yi, Mengyao Tang, Archana Soam, N. Peretto, Manash R. Samal, Michel Fich, Harriet Parsons, Jinghua Yuan, Chuan-Peng Zhang, Johanna Malinen, George J. Bendo, A. Rivera-Ingraham, Hong-Li Liu, Jan Wouterloot, Pak Shing Li, Lei Qian, Jonathan Rawlings, Mark G. Rawlings, Siyi Feng, Yuri Aikawa, S. Akhter, Dana Alina, Graham Bel, J.-P. Bernard, Andrew Blain, Rebeka B?gner, L. Bronfman, D.-Y. Byun, Scott Chapman, Huei-Ru Chen, M. Chen, Wen-Ping Chen, X. Chen, Xuepeng Chen, A. Chrysostomou, Giuliana Cosentino, M. R. Cunningham, K. Demyk, Emily Drabek-Maunder, Yasuo Doi, C. Eswaraiah, Edith Falgarone, O. Feher, Helen Fraser, Per Friberg, G. Garay, J. X. Ge, W. K. Gear, Jane Greaves, X. Guan, Lisa Harvey-Smith, Tetsuo HASEGAWA, J. Hatchell, Yuxin He, C. Henkel, T. Hirota, W. Holland, A. Hughes, E. Jarken, Tae-Geun Ji, Izaskun Jimenez-Serra, Miju Kang, Koji S. Kawabata, Gwanjeong Kim, Jungha Kim, Jongsoo Kim, Shinyoung Kim, B.-C. Koo, Woojin Kwon, Yi-Jehng Kuan, K. M. Lacaille, Shih-Ping Lai, C. F. Lee, J.-E. Lee, Y.-U. Lee1, Dalei Li, Hua-bai Li, N. Lo, John A. P. Lopez, Xing Lu, A-Ran Lyo, D. Mardones, A. Marston, P. McGehee, F. Meng, L. Montier, Julien Montillaud, T. Moore, O. Morata, Gerald H. Moriarty-Schieven, S. Ohashi, Soojong Pak, Geumsook Park, R. Paladini, Kate M Pattle, Gerardo Pech, V.-M. Pelkonen, K. Qiu, Zhi-Yuan Ren, John Richer, M. Saito, Takeshi Sakai, H. Shang, Hiroko Shinnaga, Dimitris Stamatellos, Y.-W. Tang, Alessio Traficante, Charlotte Vastel, S. Viti, Andrew Walsh, Bingru Wang, Hongchi Wang, Junzhi Wang, D. Ward-Thompson, Anthony Whitworth, Ye Xu, J. Yang, Yao-Lun Yang, Lixia Yuan, A. Zavagno, Guoyin Zhang, H.-W. Zhang, Chenlin Zhou, Jianjun Zhou, Lei Zhu, Pei Zuo, and Chao Zhang
  • 2018
  • The Astrophysical Journal Supplement Series, Volume 234, Number 2
The low dust temperatures (<14 K) of Planck Galactic cold clumps (PGCCs) make them ideal targets to probe the initial conditions and very early phase of star formation. “TOP-SCOPE” is a joint survey program targeting ∼2000 PGCCs in J = 1-0 transitions of CO isotopologues and ∼1000 PGCCs in 850 μm continuum emission. The objective of the “TOP-SCOPE” survey and the joint surveys (SMT 10 m, KVN 21 m, and NRO 45 m) is to statistically study the initial conditions occurring during star formation and the evolution of molecular clouds, across a wide range of environments. The observations, data analysis, and example science cases for these surveys are introduced with an exemplar source, PGCC G26.53+0.17 (G26), which is a filamentary infrared dark cloud (IRDC). The total mass, length, and mean line mass (M/L) of the G26 filament are ∼6200 M⊙, ∼12 pc, and ∼500 M⊙ pc^-1, respectively. Ten massive clumps, including eight starless ones, are found along the filament. The most massive clump as a whole may still be in global collapse, while its denser part seems to be undergoing expansion owing to outflow feedback. The fragmentation in the G26 filament from cloud scale to clump scale is in agreement with gravitational fragmentation of an isothermal, nonmagnetized, and turbulent supported cylinder. A bimodal behavior in dust emissivity spectral index (β) distribution is found in G26, suggesting grain growth along the filament. The G26 filament may be formed owing to large-scale compression flows evidenced by the temperature and velocity gradients across its natal cloud.
8
  • Sang-Sung Lee
  • Sincheol Kang
  • Jae-Young Kim, Sang-Sung Lee, Jeffrey A. Hodgson, Juan-Carlos Algaba, Guang-Yao Zhao, Motoki Kino, Do-Young Byun, Sincheol Kang
  • 2018
  • A&A Volume 610
We study the centimeter- to millimeter-wavelength synchrotron spectrum of the core of the radio galaxy M 87 at ≤0.8 mas ~ 110Rs spatial scales using four years of fully simultaneous, multi-frequency VLBI data obtained by the Korean VLBI Network (KVN). We find a core spectral index α of ≥-0.37 (S ∝ ν+α) between 22 and 129 GHz. By combining resolution-matched flux measurements from the Very Long Baseline Array (VLBA) at 15 GHz and taking the Event Horizon Telescope (EHT) 230 GHz core flux measurements in epochs 2009 and 2012 as lower limits, we find evidence of a nearly flat core spectrum across 15 and 129 GHz, which could naturally connect the 230 GHz VLBI core flux. The extremely flat spectrum is a strong indication that the jet base does not consist of a simple homogeneous plasma, but of inhomogeneous multi-energy components, with at least one component with the turn-over frequency ≥100 GHz. The spectral shape can be qualitatively explained if both the strongly (compact, optically thick at <100 GHz) and the relatively weakly magnetized (more extended, optically thin at <100 GHz) plasma components are colocated in the footprint of the relativistic jet.
7
  • Sang-Sung Lee
  • Sincheol Kang
  • Jeffrey A. Hodgson, Bindu Rani, Sang-Sung Lee, Juan-Carlos Algaba, Motoki Kino, Sascha Trippe, Jong-Ho Park, Guang-Yao Zhao, Do-Young Byun, Sincheol Kang, Jae-Young Kim, Jeong-Sook Kim, Soon-Wook Kim, Atsushi Miyazaki, Kiyoaki Wajima, Junghwan Oh, Dae-won Kim, Mark Gurwell
  • 2018
  • Monthly Notices of the Royal Astronomical Society, Volume 475, Issue 1
3C 84 (NGC 1275) is a well-studied misaligned sctive galactic nucleus (AGN), which hasbeen active in γ-rays since at least 2008. We have monitored the source at four wavelengths(14, 7, 3, and 2 mm) using the Korean VLBI network (KVN) since 2013 as part of theinterferometric monitoring of γ-ray bright AGN (iMOGABA) programme, and it exhibitsbright radio emission both near the central SMBH and in a slowly moving feature located tothe south known as C3. Other facilities have also detected these short-term variations abovea slowly rising trend at shorter wavelengths, such as in γ-ray and 1-mm total intensity lightcurves. We find that the variations in the γ -rays and 1-mm total intensity light curves arecorrelated, with the γ-ray leading and lagging the radio emission. Analysis of the 2-mmKVN data shows that both the γ-rays and 1-mm total intensity short-term variations are bettercorrelated with the SMBH region than C3, likely placing the short-term variations in C1. Weinterpret the emission as being due to the random alignment of spatially separated emissionregions. We place the slowly rising trend in C3, consistent with previous results. Spectralanalysis of the γ-ray data shows that the γ-ray flaring is inconsistent with blazar-like γ -rayemission. Additionally, we report that since mid-2015, a large mm-wave radio flare has beenoccurring in C3, with a large γ-ray flare coincident with the onset of this flare at all radiowavelengths.
만족도 조사
콘텐츠 담당부서ALMA그룹,천문전산융합센터
콘텐츠 만족도