• 천문학회보
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• 제41권2호
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• pp.58.1-58.1
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• 2016

During the year 2016 the newly installed NYSC (National Youth Science Center) 1m optical telescope was officially commissioned. Calls for future observational programmes were announced. During test observations we carried out an observational project aimed at follow-up observations of transiting extrasolar planets. To predict future transits we developed the "TransitSearch" code implemented in Python utilizing transit information from the Open Exoplanet Catalogue. During three nights in April and June 2016 we observed planetary transits of HAT-P-3b and TrES-3b. Preliminary light curves of the transit events are presented alongside with best-fit models. From this experience we plan to improve the optical alignment and photometric performance by operating the 1m NYSC telescope in a strongly out-of-focus mode for transit observations.

• 천문학회보
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• 제37권1호
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• pp.34.2-34.2
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• 2012

In the context of structure formation in a hierarchical Universe, the relevance of mergers to radio-loud active galaxies is still under debate. I employ two different observational approaches to investigate the merger history of active galaxies, using several different samples of radio-loud AGN. I will first show results from the investigation of a complete sample of flat-spectrum radio-AGN and their role in a merger-driven evolution of galaxies. In the second part of my talk I will focus on the investigation of the close environment of radio-loud active galaxies, using data from the new VISTA-VIDEO near-infrared survey. Strong evidence is found supporting a close connection between merger events and radio-loud AGN.

• 천문학회지
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• 제47권6호
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• pp.215-218
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• 2014

One-dimensional (1-D) microlens parallaxes can be combined with heliocentric lens-source relative proper motion measurements to derive the lens mass and distance, as suggested by Ghosh et al. (2004). Here I present the first mathematical anlysis of this procedure, which I show can be represented as a quadratic equation. Hence, it is formally subject to a two-fold degeneracy. I show that this degeneracy can be broken in many cases using the relatively crude 2-D parallax information that is often available for microlensing events. I also develop an explicit formula for the region of parameter space where it is more difficult to break this degeneracy. Although no mass/distance measurements have yet been made using this technique, it is likely to become quite common over the next decade.

• 천문학회보
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• 제42권2호
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• pp.65.4-65.4
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• 2017

The laboratory astrophysics is a new emerging field of basic sciences, and has tremendous discovery potentials. The laboratory astrophysics investigates the basic physical phenomena in the astrophysical objects in controlled and reproducible manners, which has become possible only recently due to the newly-established intense photon and ion beam facilities worldwide. In this presentation, we will introduce several promising ideas for laboratory astrophysics programs that might be readily incorporated in the Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL). For example, precise spectroscopic measurements using Electron Beam Ion Trap (EBIT) and intense X-ray photons from the PAL-XFEL can be performed to explore the fundamental processes in high energy X-ray phenomena in the visible universe. Besides, in many violent astrophysical events, the energy density of matter becomes so high that the traditional plasma physics description becomes inapplicable. Generation of such high-energy density states can be also be achieved by using the intense photon beams available from the PAL-XFEL.

• 천문학회지
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• 제49권4호
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• pp.123-126
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• 2016

Microlensing is generally thought to probe planetary systems only out to a few Einstein radii. Microlensing events generated by bound planets beyond about 10 Einstein radii generally do not yield any trace of their hosts, and so would be classified as free floating planets (FFPs). I show that it is already possible, using adaptive optics (AO), to constrain the presence of potential hosts to FFP candidates at separations comparable to the Oort Cloud. With next-generation telescopes, planets at Kuiper-Belt separations can be probed. Next generation telescopes will also permit routine vetting for all FFP candidates, simply by obtaining second epochs 4-8 years after the event. At present, the search for such hosts is restricted to within the "confusion limit" of θ_confus ∼ 0.25′′, but future WFIRST (Wide Field Infrared Survey Telescope) observations will allow one to probe beyond this confusion limit as well.

• 천문학회보
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• 제35권2호
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• pp.50.2-50.2
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• 2010

Magnetic helicity injection in 28 solar active regions producing 46 CMEs was investigated to find its relationship with the occurrence and speed of CMEs. The helicity injection in the active regions under investigation was calculated using full-disk 96 minute MDI magnetograms. The major findings of this study are as follows. First, the 46 CMEs are categorized into two different groups by two characteristic evolution patterns of helicity injection in their active regions: (1) a monotonically increasing of helicity accumulation (Group A; 30 CMEs in 23 active regions) and (2) significant helicity injection followed by its sign reversal (Group B; 16 CMEs in 5 active regions). Second, a fairly good correlation between the helicity injection rate and the CME speed is found for the 30 CME events in Group A. Further statistical studies, however, are needed to check whether the two characteristic helicity patterns are shown in other CME-productive active regions.

• 천문학회보
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• 제35권1호
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• pp.66.1-66.1
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• 2010

Using two-dimensional numerical hydrodynamic simulations, we investigate the star formation rate (SFR) in turbulent, multiphase, galactic gaseous disks. Our simulation domain is axisymmetric, and local in the radial direction and global in the vertical direction. Our models include galactic rotation, vertical density stratification, self-gravity, radiative heating and cooling, and thermal conduction, but do not include spiral-arm features. Turbulence in our models is driven by momentum feedback from supernova explosion events occurring in localized dense regions formed by thermal and gravitational instabilities. Self-consistent radiative heating, representing enhanced/reduced FUV photons from the star formation, is also taken into account. By controlling three parameters (the gas surface density, the stellar disk density, and the angular rotation rate) that characterize local galactic disks, we explore how the SFR depends on the background environmental state. We also discuss the relation between the SFR and the gas surface density found in our numerical models in comparison with observations.

• 천문학회보
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• 제35권2호
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• pp.74.1-74.1
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• 2010

Using two-dimensional numerical hydrodynamic simulations, we investigate the regulation of star ormation rates in turbulent, multiphase, galactic gaseous disks. Our simulation domain is xisymmetric, and local in the radial direction and global in the vertical direction. Our models nclude galactic rotation, vertical stratification, self-gravity, heating and cooling, and thermal onduction. Turbulence in our models is driven by momentum feedback from supernova events ccurring in localized dense regions formed by thermal and gravitational instabilities. Self-onsistent radiative heating, representing enhanced/reduced FUV photons from the star formation, s also taken into account. Evolution of our model disks is highly dynamic, but reaches a quasi-teady state. The disks are overall in effective hydrostatic equilibrium with the midplane thermal ressure set by the vertical gravity. The star formation rate is found to be proportional pproximately linearly to the midplane thermal pressure. These results are in good agreement with the predictions of a recent theory by Ostriker, McKee, and Leroy (2010) for the thermal/dynamic equilibrium model of star formation regulation.

• 천문학회보
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• 제42권1호
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• pp.37.3-37.3
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• 2017

We present a novel GPU accelerated search algorithm for broadband extended gravitational-wave emission (BEGE) with better than real-time analyis of H1-L1 LIGO S6 data. It performs matched filtering with over 8 million one-second duration chirps. Parseval's Theorem is used to predict the standard deviation ${\sigma}$ of filter output, taking advantage of near-Gaussian LIGO (H1,L1)-data in the high frequency range of 350-2000 Hz. A multiple of ${\sigma}$ serves as a threshold to filter output back to the central processing unit. This algorithm attains 80% efficiency, normalized to the Fast Fourier Transform (FFT). We apply it to a blind, all-sky search for BEGE in LIGO data, such as may be produced by long gamma-ray bursts and superluminous supernovae. We report on mysterious features, that are excluded by exact simultaneous occurrance. Our results are consistent with no events within a radius of about 20 Mpc.

• 천문학회보
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• 제42권1호
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• pp.48.4-49
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• 2017

We aim to trace cosmic mass accretion history of satellites around a dwarf galaxy in Lambda-CDM cosmology frame. Each satellite has a unique mass accretion history due to different environment, potential depth, and different merging events. We perform three different zoom simulations whose target galaxy has a mass of ${\sim}10^{10}Msun$, using ~17 million particles covering a cubic box of $1(Mpc/h)^3$. Here, individual particle masses for dark matter (DM) and gas are $M_{DM}=4.1{\times}10^3Msun$ and $Mgas=7.9{\times}10^2Msun$, respectively, and thus each satellite can be resolved with more than several hundreds of particles.