• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.54.2-54.2
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• 2015

Phase referencing is an important tool to study weak radio sources, especially in mm-VLBI (Very Long Baseline Interferometry) which are usually too faint to be observed using conventional VLBI. VLBI astrometry is a unique method to measure the position and to identify radio emitting regions of a radio source with unprecedented angular resolution. In order to evaluate the phase referencing and astrometric capabilities of KVN and KaVA, several observations have been conducted and analyzed. I will present the observational results and discuss constraints and requirements for high precision VLBI astrometry.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.47.1-47.1
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• 2017

Thanks to the quasi-optics system of KVN, the relative astrometry at different frequencies can be effectively achieved. In this talk, as a part of the KVN special session, we are going to present an important method making it possible, so called the source frequency phase referencing (SFPR). Based on the background, we will show our recent activities using the SFPR for the Galactic Center (Sgr A*) study, from its advantages on astrometric studies to the remained issues.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.69.1-69.1
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• 2011

The multi-band receiving feed which is one of the unique characteristics of the Korean VLBI Network (KVN) system compare to the other VLBI network enables to study precise astrometry with a source frequency phase referencing (SFPR) techniques. SFPR almost perfectly compensates the dominant non-dispersive tropospheric fluctuations by observing sources with multi-frequency simultaneously, and it also corrects the dispersive ionospheric fluctuations by adding a slow source-switching observation. In this talk, I will present the results from the KVN astrometric observations with SFPR and the achievable astrometric accuracy in KVN will be discussed.

• Journal of The Korean Astronomical Society
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• v.48 no.5
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• pp.277-284
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• 2015

We present our efforts for extending the simultaneous multi-frequency receiver system of the Korean Very Long Baseline Interferometry (VLBI) Network (KVN) to global baselines in order to measure the frequency-dependent position shifts in Active Galactic Nuclei (AGN) jets, the so called core shift effect, with an unprecedented accuracy (a few micro-arcseconds). Millimeter VLBI observations with simultaneous multi-frequency receiver systems, like those of the KVN, enable us to explore the innermost regions of AGN and high precision astrometry. Such a system is capable of locating the frequency dependent opacity changes accurately. We have conducted the feasibility test-observations with the interested partners by implementing the KVN-compatible systems. Here we describe the science case for measuring the core shift effect in the AGN jet and report progress and future plans on extending the simultaneous multi-frequency system to global baselines.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.425-426
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• 1996

A few optical schemes for the future Russian astrometric satellite ('Struve') are discussed. New optical materials and techniques developed at the Vavilov State Optical Institute are planned to be used for the on-board telescopes. Optical characteristics of the reflecting Schmidt and a three - mirror scheme for the on-board telescopes are compared.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.427-428
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• 1996

The Struve astrometric satellite which is being developed at Pulkovo Observatory in cooperation with Krasno-yarsk Institute of Applied Mechanics, S.I. Vavilov's State Optical Institute and some others space instrumentation institutes, will produce observations of a second epoch for the Hipparcos stars. The project is devoted to maintaining the Hipparcos coordinate system as well as extending it to a density of $\approx$ 100 stars per square degree. Possibilities of submilliarcsecond accuracy of observations with single aperture on-board telescopes are discussed. Requirements to the optical scheme and to the dynamic properties of the spacecraft are formulated. CCD and microchannel plates are discussed as a focal assembly detectors.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.60.1-60.1
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• 2011

We present the preliminary results of the pilot observations for the fringe survey at 43 GHz with the VLBI Exploration of Radio Astrometry (VERA). The main goals of the fringe survey are to establish a full list of phase calibrators for the VERA dual-beam astrometric observations, and for the KVN multi-frequency phase referencing observations. We performed two 24 hours experiments as a pilot observation to test the feasibility of the fringe survey. Each source from a list of 220 sources has been observed in one scan for 2 minutes. 67 sources were detected with the SNR threshold of 3.5. The correlated flux densities of the detected sources are presented in four ranges of projected baseline lengths.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.112.1-112.1
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• 2014

KVN은 현재 연간 3000시간 이상의 VLBI 관측 시간을 운영하는 안정적인 운영단계에 들어섰다. 또한 일본의 VLBI 관측망인 VERA와 연결한 KaVA (KVN and VERA Array)도 한일상관센터의 운영시작과 더불어 연간 1000 시간의 관측 운영을 하고 있으며 KaVA를 이용한 연구 성과가 나오기 시작하였다. KVN은 다파장 Astrometry를 위해 다파장 P-Cal 시스템을 개발하고 있으며 관측 감도를 높이기 위해 8Gbps 운영을 준비하고 있다. KVN의 운영 및 시스템 개선 계획, 국제 협력 내용 등을 소개한다.

• 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).

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.43.1-43.1
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• 2010

We have carried out 43-GHz VLBI test observations of the Korean VLBI Network (KVN), which has obtained the first fringes at 22/43-GHz in 2009 (a talk by Sohn, Bong Won). In collaboration with VERA (VLBI Exploration of Radio Astrometry) in Japan, we have observed Active Galactic Nuclei (AGNs) and Orion-KL at 43GHz on 22nd and 23rd December, 2009, in order to evaluate the baseline- and image-sensitivity of KVN and KVN+VERA. In this talk we report the preliminary results of the VLBI test observations of the Korean VLBI Network at 43GHz.