• Journal of The Korean Astronomical Society
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• v.34 no.2
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• pp.81-97
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• 2001

Since the first proposal by Paczynski, great efforts to detect Galactic dark matter by detecting light variations of stars located in the Magellanic Clouds and Galactic bulge caused by gravitational microlensing have been and are being carried out and more than 1,000 events have been successfully detected. In this paper, we review the progress in the theoretical and experimental progresses in microlensing. We begin with basics of microlensing and summarize the results obtained from the last 8 year observations along with the implications of the results. We also discuss the usefulness of microlensing in other fields of astronomy such as the stellar atmosphere, Galactic binary systems, and extra-solar planets. We finally discuss the problems of the current experiments and the new types of observations that can overcome these problems.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.71.1-71.1
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• 2011

한일상관센터(Korea-Japan Correlation Center, KJCC)는 한국천문연구원이 일본국립천문대와 공동으로 2006년부터 개발한 한일공동VLBI상관기(Korea-Japan Joint VLBI Correlator, KJJVC)의 설치를 2010년 완료하였으며, 2010년 5월 13일에 개소하였다. 한일상관센터에 설치된 한일공동VLBI상관기는 한국우주전파관측망(Korean VLBI Network, KVN), VERA(VLBI Exploration of Radio Astrometry), JVN(Japanese VLBI Network), 그리고 중국의 Chinese VLBI Network(CVN)을 연결하여 관측한 동아시아 지역의 VLBI 관측데이터의 상관처리를 2011년 하반기부터 정상적으로 수행할 예정이다. 한일상관센터의 정상운영을 위해 각 하드웨어 시스템들의 시험운영을 진행하고 있으며, KVN과 VERA로 관측한 VLBI 관측데이터의 상관처리를 진행하고 있다. 특히 상관분석 소프트웨어 부분에서 상관처리 결과를 과학적 목적으로 분석할 수 있는 상관후처리 소프트웨어 개발을 한일공동으로 진행하고 있으며, 현재 소프트웨어 디버깅 작업을 진행하고 있다. 본 발표에서는 한일상관센터의 전체적인 하드웨어 및 소프트웨어 구성, 상관결과 분석방법, 운영방법 등의 내용을 중심으로 기술한다.

• Journal of The Korean Astronomical Society
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• v.50 no.1
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• pp.1-5
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• 2017

Like Hipparcos, Gaia is designed to give absolute parallaxes, independent of any astrophysical reference system. And indeed, Gaia's internal zero-point error for parallaxes is likely to be smaller than any individual parallax error. Nevertheless, due in part to mechanical issues of unknown origin, there are many astrophysical questions for which the parallax zero-point error ${\sigma}({\pi}_0)$ will be the fundamentally limiting constraint. These include the distance to the Large Magellanic Cloud and the Galactic Center. We show that by using the photometric parallax estimates for RR Lyrae stars (RRL) within 8kpc, via the ultra-precise infrared period-luminosity relation, one can independently determine a hyper-precise value for ${\pi}_0$. Despite their paucity relative to bright quasars, we show that RRL are competitive due to their order-of-magnitude improved parallax precision for each individual object relative to bright quasars. We show that this method is mathematically robust and well-approximated by analytic formulae over a wide range of relevant distances.

• Journal of Astronomy and Space Sciences
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• v.26 no.4
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• pp.567-588
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• 2009

Korea-Japan Joint VLBI Correlator (KJJVC) is being developed by collaborating KASI (Korea Astronomy and Space Science Institute), Korea, and NAOJ(National Observatory of Japan), Japan. In early 2010, KJJVC will work in normal operation. In this study, we developed the software correlator which is based on VCS (VLBI Correlation Subsystem) hardware specification as the core component of KJJVC. The main specification of software correlator is 8 Gbps, 8192 output channels, and 262,144-points FFT (Fast Fourier Transform) function same as VCS. And the functional algorithm which is same as specification of VCS and arithmetic register are adopted in this software correlator. To verify the performance of developed software correlator, the correlation experiments were carried out using the spectral line and continuum sources which were observed by VERA (VLBI Exploration of Radio Astrometry), NAOJ. And the experimental results were compared to the output of Mitaka FX correlator by referring spectrum shape, phase rate, and fringe detection and so on. Through the experimental results, we confirmed that the correlation results of software correlator are the same as Mitaka FX correlator and verified the effectiveness of it. In future, we expect that the developed software correlator will be the possible software correlator of KVN (Korean VLBI Network) with KJJVC by introducing the correlation post-processing and modifying the user interface as like GUI (Graphic User Interface).

• Journal of the Institute of Convergence Signal Processing
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• v.12 no.4
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• pp.333-340
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• 2011

KJJVC(Korea-Japan Joint VLBI Correlator) was installed at the KJCC(Korea-Japan Correlation Center) and has been operated by KASI(Korea Astronomy and Space Science Institute) from 2009. KJNC is able to correlate the VLBI observed data through KVN(Korean VLBI Network), VERA(VLBI Exploration of Radio Astrometry), and JVN(Japanese VLBI Network) and its joint network array. And it is used exclusively as computer in order to process the observed data for the scientific purpose KJJVC used the VSI(VLBI Standard Interface) as the VLBI international standard at the data input-output specification between each component. Especially, for correlating the observed data, the data is transmitted with 1024Mbps speed between Mark5B high-speed playback and RVDB(Raw VLBI Data Buffer). The EMI(Electromagnetic lnterference), which is occurred by data transmission with high-speed, cause the data loss and the loss occurrence is frequently often for long transmission cable. Finally it will be caused the data recognition error by decreasing the voltage level of digital data signal. In this paper, in order to minimize the data loss by measuring the EMI noise level in transmission of the VSI specification, the 3 methods such as 1) RC filtering method, 2) lmpedance matching using Microstrip line, and 3) Signal buffering method using Differential line driver, were proposed. To verify the effectiveness of each proposed method, the performance evaluation was conducted by implementing and simulations for each method. Each proposed method was effectively confirmed as the high-speed data transmission of the VSI specification.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.145-146
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• 2012

We present the results from B-, R-, I-, J- and H-band observations of the NEP-Wide survey field. The NEP-Wide survey is an AKARI survey of the North Ecliptic Pole covering ~ 5 square degrees area. Our optical/NIR imaging supports the AKARI IR imaging data by providing a crucial coverage in the optical/NIR. The optical data were obtained in 2007 using the 1.5 m telescope and SNUCAM at Maidanak Observatory, Uzbekistan. The NIR data were obtained in 2008 with FLAMINGOS on the KPNO 2.1 m telescope. We used IRAF, SExtractor, SCAMP, and SWarp for reducing the raw data, I-band fringe pattern removal, astrometry, standard photometry calibration, and source detection. Our optical-NIR data reach the depths of B ~ 23.4, R ~ 23.1, I ~ 22.3, J ~ 21.05, and H ~ 20.64 AB mag at 5-sigma. Here, we present the astrometric accuracy, galaxy number counts, completeness, and reliability, as well as redshift tracks of some normal galaxies and quasars on the B - R vs. R - I color-color diagram. The photometric data are being used for identifying optical counterparts of the IR data provided by AKARI, studying their SEDs, and selecting interesting objects for spectroscopic follow-up studies.

• Journal of Astronomy and Space Sciences
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• v.37 no.3
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• pp.171-185
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• 2020

This paper presents a methodology for Initial Orbit Determination (IOD) based on a modification of the Laplace's geocentric method. The orbital elements for Near-Earth asteroids (1864) Daedalus, 2003 GW, 2019 JA8, a Hungaria-type asteroid (4690) Strasbourg, and the asteroids of the Main Belt (1738) Oosterhoff, (2717) Tellervo, (1568) Aisleen and (2235) Vittore were calculated. Input data observations from the Minor Planet Center MPC database and Astronomical Observatory of the Technological University of Pereira (OAUTP; MPC code W63) were used. These observations cover observation arcs of less than 22 days. The orbital errors, in terms of shape and orientation for the estimated orbits of the asteroids, were calculated. The shape error was less than 53 × 10^-3 AU, except for the asteroid 2019 JA8. On the other hand, errors in orientation were less than 0.1 rad, except for (4690) Strasbourg. Additionally, we estimated ephemerides for all bodies for up to two months. When compared with actual ephemerides, the errors found allowed us to conclude that these bodies can be recovered in a field of vision of 95' × 72' (OAUTP field). This shows that Laplace's method, though simple, may still be useful in the IOD study, especially for observatories that initiate programs of minor bodies observation.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.60.2-60.2
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• 2010

대기의 불규칙한 수증기 분포로 인해 VLBI 관측시 visibility 위상에 불규칙한 변화가 발생한다. 이를 보정하기 위해 phase-referencing 기법 등을 이용할 수 있다. KVN calibrator survey는 Phase-referencing 기법에 필수적인 위상보정 calibrator를 얻기 위한 연구이다. 2, 8GHz 대역에서 관측된 VLBA(Very Long Baseline Array) Calibrator Survey(VCS) 목록을 기초로 power-law를 가정하여 22GHz에서 100mJy 이상일 것으로 예상되는 천체 2503개를 KVN Calibrator Survey의 대상으로 선정하였다. 먼저 KVN 연세 전파망원경을 이용하여 2009년 12월부터 2010년 6월까지 22GHz에서 500mJy 이상으로 예상되는 천체 595개에 대한 플럭스 측정 관측을 진행하였고 22GHz에서 517개, 43GHz에서 226개의 천체를 검출하였다. 이어 200mJy 이상 500mJy 미만으로 예상되는 천체 983개에 대하여 추가 관측을 진행하고 있다. 그리고 플럭스가 측정된 천체들에 대하여 VLBI Exploration of Radio Astrometry(VERA)와 VLBA, 각각 K밴드에서 관측된 결과와 비교하여 중복되지 않은 천체들에 대해 VLBI 관측을 수행하여 천체의 위치와 구조에 대한 정보를 얻을 계획이다.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.59.1-59.1
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• 2010

We have carried out VLBI test observations of the Korean VLBI Network (KVN) at 22/43-GHz in collaboration with Japanese VLBI Exploration of Radio Astrometry (VERA). In order to evaluate the VLBI system of KVN, we have observed several sources using KVN+VERA. They consist of Active Galactic Nuclei (AGNs), which are expected to be compact and to have very well-known structures at spatial resolutions of 50-250 Mega-wavelengths, and Galactic star-forming regions and late-type stars, which have bright H2O and SiO maser emission regions. We have investigated baseline and imaging sensitivities of KVN+VERA. In this talk we report the preliminary results.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.59.2-59.2
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• 2010

We have carried out VLBI test observations of the Korean VLBI Network (KVN) at 22/43-GHz in collaboration with Japanese VLBI Exploration of Radio Astrometry (VERA). In order to evaluate the VLBI system of KVN, we have observed several sources using KVN+VERA. They consist of Active Galactic Nuclei (AGNs), which are expected to be compact and to have very well-known structures at spatial resolutions of 50-250 Mega-wavelengths, and Galactic star-forming regions and late-type stars, which have bright H2O and SiO maser emission regions. We have investigated baseline and imaging sensitivities of KVN+VERA. In this talk we report the preliminary results.