• Bulletin of the Korean Space Science Society
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• 2007.10a
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• pp.57.2-57.2
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• 2007

• The Bulletin of The Korean Astronomical Society
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• v.33 no.2
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• pp.38.1-38.1
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• 2008

• Bulletin of the Korean Space Science Society
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• 2009.04a
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• pp.56.1-56.1
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• 2009

• Bulletin of the Korean Space Science Society
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• 2009.04a
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• pp.56.2-56.2
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• 2009

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.40.2-40.2
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• 2019

Measuring distances at cosmological scales is one of the most important, yet most difficult to acquire astronomical quantities, allowing astronomers to determine the expansion rate of the universe. Typically, astronomers have sought to find "standard candles" that have a known intrinsic brightness in order to determine their distance. The most well known standard candles are Type 1a supernova and Cepheid variable stars making the so-called "distance ladder". Here we present a method for determining cosmological distances via light travel-time arguments, which can be extended from nearby sources to very high redshift sources.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.61.4-61.4
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• 2021

Searching for technosignatures is the fundamental tool for finding the evidence of the extraterrestrial life in the Universe along with searching for biosignatures. We summarize the current status of the radio SETI(Search for Extraterrestrial Intelligence) such as the Breakthrough Listen project and suggest a concept of the VLBI SETI with KVN(Korean VLBI Network). In addition, we introduce conceptual studies of the SETI on the surface of Moon's farside and in lunar orbit.

• Journal of The Korean Astronomical Society
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• v.56 no.1
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• pp.91-96
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• 2023

In this paper, we describe the first multi-frequency synthesis observations of blazar 0059+581 made with the Radioastron space-ground interferometer in conjunction with the Korean VLBI Network (KVN), Medicina and Torun ground telescopes. We conducted these observations to assess the spaceground interferometer multi-frequency mode capability for the first time.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.52.2-52.2
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• 2015

SgrA* located in the center of the Milky Way is of great interest to understand the physics of supermassive black hole(SMBH) and the interaction of the G2 cloud around SgrA* with the accretion flow which was expected since 2013. In order to seize this rare opportunity, KVN and VERA Array (so called, KaVA) has started an intensive monitoring program of SgrA* at 22/43 GHz where scatter broadening is reduced compared to lower frequency VLBI observations. We present the results of KaVA SgrA* observation together with Takahagi (32m) and Yamaguchi (32m) telescopes at 22 GHz on March 24, 2013. We have tested both a standard amplitude calibration methods using the Tsys and antenna gain information and a template amplitude calibration method which uses a peak of H2O maser line of nearby maser source (SgrB2), and found that the latter method is useful when an accuracy of Tsys measurement or antenna gain of a telescope is poor. In our comparison, the difference between the two methods is around 20% (~5% for the KVN and ~15% for the VERA when the elevation is above $20^{\circ}$). We also imaged SgrA* with a total flux of ~0.7 Jy at 22GHz, and fitted an elliptical Gaussian model which has a size of ~2.5mas for major axis and ~1.7mas for minor axis, respectively.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.66.1-66.1
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• 2013

We present various observational results toward a small group of Young Stellar Objects (YSOs), L1251C. Observations by Spitzer Space Telescope legacy program "From Molecular Cores to Planet Forming Disks" (c2d; Evans et al. 2003) revealed that there are three YSOs within ~15" in L1251C: IRS1 (Class I), IRS2 (Class II), and IRS3 (Class II). In order to understand the molecular environment around these YSOs, we carried out the KVN single-dish observations in $HCO^+$ J=1-0, $H^{13}CO^+$ J=1-0, $N_2H^+$ J=1-0 and HCN J=1-0. $^{12}CO$ J=1-0 was also mapped in L1251C with the TRAO 14m telescope. Integrated intensity maps of high density tracers such as $H^{13}CO^+$ J=1-0, $N_2H^+$ J=1-0 and HCN J=1-0 show similar emission distributions, whose peaks are off the positions of YSOs. A compact $HCO^+$ J=1-0 outflow and an extended $^{12}CO$ J=1-0 outflow were observed, but their outflow axes are not cosistent ($HCO^+$: NW-SE, $^{12}CO$: EW). However, the highest velocity component of the $^{12}CO$ J=1-0 outflow shows similar morphology to the $HCO^+$ J=1-0 outflow, and ~ 23 % of $^{12}CO$ outflow momentum flux is loaded onto this high velocity component. Furthermore, continuum emission has been observed at 350, 450, 850 ${\mu}m$, and 1.3mm. With the KVN single dish, the 22 GHz $H_2O$ maser emission has been also monitored toward L1251C to find variations of the systemic velocity and intensity with time.

• Journal of Astronomy and Space Sciences
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• v.27 no.2
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• pp.107-116
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• 2010

We developed the playback control software for a high-speed playback system which is a component of the Korea-Japan Joint VLBI Correlator (KJJVC). The Mark5B system, which is a recorder and playback system used in the Korean VLBI Network (KVN), has two kinds of operation mode. That is to say, the station unit (SU) mode, which is for the present Mark4 system, and the VSI mode, which is for the new VLBI standard interface (VSI) system. The software for SU is already developed and widely used in the Mark4 type VLBI system, but the software for VSI has only been developed for recording. The new VLBI system is designed with a VSI interface for compatibility between different systems. Therefore, the playback control software development of the VSI mode is needed for KVN. In this work, we developed the playback control software of the Mark5B VSI mode. The developed playback control software consists of an application part for data playing back, a data input/output part for the VSI board, a module for the StreamStor RAID board, and a user interface part, including an observation time control part. To verify the performance of developed playback control software, the playback and correlation experiments were performed using the real observation data in Mark5B system and KJJVC. To check the observation time control, the data playback experiment was performed between the Mark5B and Raw VLBI Data Buffer (RVDB) systems. Through the experimental results, we confirmed the performance of developed playback control software in the Mark5B VSI mode.