• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.44.1-44.1
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• 2015

We set up a project to make spectrometers for single dish observations of the Korean VLBI Network (KVN), a new future multi-beam receiver of the ASTE (Atacama Submillimeter Telescope Experiment), and the total power (TP) antennas of the Atacama Large Millimeter/submillimeter Array (ALMA). Traditionally, spectrometers based on ASIC (Application-Specific Integrated circuit) and FPGA (Field-Programmable Gate Array) have been used in radio astronomy. It is, however, that a Graphics Processing Unit (GPU) technology is now viable for spectrometers due to the rapid improvement of its performance. A high-resolution spectrometer should have the following functions: poly-phase filter, data-bit conversion, fast Fourier transform, and complex multiplication. We wrote a program based on CUDA (Compute Unified Device Architecture) for a GPU spectrometer. We measured its performance using two GPU cards, Titan X and K40m, from NVIDIA. A non-optimized GPU code can process a data stream of around 2 GHz bandwidth, which is enough for the KVN spectrometer and promising for the ASTE and ALMA TP spectrometers.

• The Bulletin of The Korean Astronomical Society
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• v.33 no.1
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• pp.62.1-62.1
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• 2008

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.234.2-234.2
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• 2012

As the accuracy in the measurement of cosmological parameters is ever-increasing in this era of precision cosmology, astrophysical constraints on high-redshift universe is also getting tighter. Three dimensional (3D) tomography of the high-redshift (z>~7) universe is expected to be made through the next-generation radio telescopes including various SKA pathfinders and SKA itself, which calls for extensive theoretical predictions. We present our new simulations of cosmic reionization covering the full dynamic range of radiation sources, and also the mock data for the (1) large-scale CMB polarization anisotropy for Planck mission, (2) small-scale, kinetic Sunyaev-Zel'dovich effect for South Pole Telescope project, and (3) 21-cm observations. We show that the new constraints on CMB from Planck will constrain the models of reionization significantly, which then should be tested by 3D tomography of high-redshift universe through the 21-cm observations by future radio telescopes.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.41.2-41.2
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• 2019

The B-fields In STar-forming Region Observations (BISTRO 1 and 2) is a large program of the James Clerk Maxwell Telescope (JCMT) using SCUBA-2 and POL-2, starting in 2016. We aim to study the roles of magnetic fields in star formation by observing 32 fields of nearby low-mass and high-mass star forming regions. The angular resolution and the wavelength provided by JCMT (14 arcsecond at 850 micrometer) are ideal to investigate the intermediate scales of magnetic fields (1000-20000 au) associated in cold dense cores and filaments. We report the current status of this project and discuss the magnetic fields of the Serpens Main molecular cloud in which several filaments with various physical properties have been identified.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.56.1-56.1
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• 2015

The GMT-Consortium Large Earth Finder (G-CLEF) is the very first light instrument of the Giant Magellan Telescope (GMT) and an optical-band echelle spectrograph. The Flexure Control Camera (FCC) is one of the major contributions of KASI's for the spectrograph project. FCC system includes the Fiber Mirror monitoring and the on- and off-slit mode auto-guidance algorithm. In this study, we present the modified design of the FCC optics and opto-mechanics after the G-CLEF Preliminary Design Review (PDR) held in Cambridge in April 2015.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.57.2-57.2
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• 2016

Polarimetry is an important tool for studying the physical processes in the interstellar medium, including star-forming regions. Polarimetry of young stellar objects and their circumstellar structures provides invaluable information about distributions of matter and configurations of magnetic fields in their environments. However, only a few near-infrared circular polarization (CP) observations were reported so far (before our survey). A systematic near-infrared CP survey has been firstly conducted in various star-forming regions, covering high-mass, intermediate-mass, and low-mass young stellar objects. All the observations were made using the SIRPOL imaging polarimeter on the Infrared Survey Facility (IRSF) 1.4 m telescope at the South African Astronomical Observatory (SAAO). In this presentation, we present the first CP survey results. The polarization patterns, extents, and maximum degrees of circular and linear polarizations are used to determine the prevalence and origin of CP in the star-forming regions. Our results are explained with a combination of circumstellar scattering and dichroic extinction mechanism generating the high degrees of CP in star-forming regions. The universality of the large and extended CPs in star-formaing regions can also be linked with the origin of homochirality of life.

• Publications of The Korean Astronomical Society
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• v.20 no.1 s.24
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• pp.21-27
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• 2005

We have been performing a wide-field photometric monitoring program, named SPVS (Short-Period Variability Survey), at the Bohyunsan Optical Astronomy Observatory (BOAO). The observation system consists of a small refracting telescope (D = 155 mm, f = 1050 mm) and a $2k{\times}3k$ CCD Camera. The field of view is $1.0^{\circ}{\times}1.5^{\circ}$. Detection limit is about V = 13 for short-period small amplitude variables such as ${\delta}$ Scuti-type pulsating stars, and about V = 15 for long-period large amplitude variables such as eclipsing binaries and RR Lyrae stars. The instrument is designed to be remote-controlled through internet. The primary purpose of this project is to search for variable objects in bright Galactic open clusters. We present results of test observations conducted towards NGC 7092.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.44.2-44.2
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• 2017

Multiple stellar systems composed of triple, double+double or double+triple, etc. are very rare and interesting objects for understanding the star formation and dynamical evolution. However, only six systems have been found to be a doubly eclipsing quadruple, which consists of two eclipsing binaries, and four systems to be a triply eclipsing hierarchical triple. Recently, the 15 doubly eclipsing multiple candidates located in the Large Magellanic Cloud (LMC) have been reported by the OGLE project. In order to examine whether these candidates are real multiple systems with eclipsing features, we performed a high-cadence time-series photometry for the LMC using the KMTNet (Korea Microlensing Telescope Network) 1.6 m telescopes in three site (CTIO, SAAO, and SSO) during 2016-2017. The KMTNet data will help reveal the photometric properties of the multiple-star candidates. In this paper, we present the VI light curves and their preliminarily analyses for 12 of the 15 eclipsing systems in the LMC, based on our KMTNet observations and the OGLE-III survey data from 2001-2009.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.63.1-63.1
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• 2019

Solar system small bodies are unusual objects in astronomical survey data in that they are moving on the celestial sphere. In addition, even in a normal status, their magnitudes are changing over time, firstly because their relative positions with respect to the Sun and Earth are continually changing, secondly because they are rotating bodies with non-spherical shapes. Furthermore, some of them might exhibit unexpected activities, which could be caused by mass ejection or disintegration. Detections and observations of such activities are challenging due to their abrupt nature. Therefore, continuous monitoring observations of large number of Solar system small bodies are required to systematically obtain detailed/transient information about them. Since 2018/2019 winter, we have launched a new project using Korea Microlensing Telescope Network (KMTNet) for detecting such transient phenomena of Solar system objects. Our main goal is to monitor the magnitudes and detect sudden brightness changes. We also plan to discover interesting new objects, and monitor rotational brightness oscillations of asteroids. We intend to monitor the magnitudes of ~ 20,000 known Solar system small bodies per night, and acquire lightcurves of ~ 1,000 asteroids.

• Journal of Astronomy and Space Sciences
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• v.22 no.4
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• pp.473-482
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• 2005

Many technical challenges are being tried for a large space infrared telescope, which is one of the major objectives of the Strategic Technology Road Map (STRM) of KASI (Korea Astronomy and Space Science Institute), As one of these challenges, KASI and KBSI (Korea Basic Science Institute) have started a cooperation project for developing a space infrared cryogenic system with KIMM (Korea Institute of Machinery as Materials) and i3system co. In this paper, we generate optical requirements for the Protomodel of Space Infrared Cryogenic System (PSICS), and design a single lens optical system with a bandpass of $3.8\~4.8{\mu}m$, a field of view of $15^{\circ}\times12^{\circ}$, and an angular resolution of $0.047^{\circ}$, to develop a further complex optical system.