• Journal of The Korean Astronomical Society
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• v.43 no.4
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• pp.135-139
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• 2010

We present the result of our investigation on the impact of the low Solar abundance of Asplund and collaborators (2004) on the derived ages for the oldest star clusters based on isochrone fittings. We have constructed new stellar models and corresponding isochrones using this new solar mixture with a proper Solar calibration. We have found that the use of the Asplund et al. (2004) metallicity causes the typical ages for old globular clusters in the Milky Way to be increased roughly by 10%. Although this may appear small, it has a significant impact on the interpretation for the formation epoch of Milky Way globular clusters. The Asplund et al. (2004) abundance may not necessarily threaten the current concordance cosmology but would suggest that Milky Way globular clusters formed before the reionization epoch and before the main galaxy body starts to build up. This is in contrast to the current understanding on the galaxy formation.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.27.4-28
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• 2015

The GMT-Consortium Large Earth Finder (G-CLEF) is an optical band echelle spectrograph that has been selected as the first light instrument for the Giant Magellan Telescope (GMT). G-CLEF is a general purpose high dispersion instrument that is fiber-fed and capable of extremely precise radial velocity measurements. G-CLEF has undergone a preliminary design review in April 2015 and is now entering final design phase and construction. G-CLEF has been designed to measure the mass of Earth-analogue exoplanets and to make critical observations in near-field and high-Z cosmology. We describe the G-CLEF instrument and several key science missions that shaped the development of G-CLEF. First light on the GMT is scheduled for late 2020.

• Journal of Astronomy and Space Sciences
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• v.32 no.2
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• pp.151-159
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• 2015

The fundamental conception in physics of the propagation of the electromagnetic wave polarization in matter is newly understood as the cardinal keyword in free-space quantum communication technology and cosmology in astrophysics. Interactive visualization of the propagation mechanism of polarized electromagnetism in a medium with its helicity has accordingly received attention from scientists exploiting the protocol of quantum key distribution (QKD) to guarantee unconditional security in cryptography communication. We have provided a dynamic polarization platform for presenting the polarization modes of a transverse electromagnetic wave, converting the state of polarization through the arrangement of optical elements, using Jones vectors calculations in Methematica. The platform graphically simulates the mechanism of production and propagation of the polarized waves in a medium while satisfying Maxwell's equations.

• Journal of The Korean Astronomical Society
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• v.48 no.3
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• pp.191-194
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• 2015

Massive gravity provides a natural solution for the dark energy problem of cosmology and is also a candidate for resolving the dark matter problem. I demonstrate that, assuming reasonable scaling relations, massive gravity can provide for Milgrom’s law of gravity (or “modified Newtonian dynamics”) which is known to remove the need for particle dark matter from galactic dynamics. Milgrom’s law comes with a characteristic acceleration, Milgrom’s constant, which is observationally constrained to a₀ ≈ 1.1 × 10⁻¹⁰ ms⁻² . In the derivation presented here, this constant arises naturally from the cosmologically required mass of gravitons like , with Λ, H₀, and Ω_Λ being the cosmological constant, the Hubble constant, and the third cosmological parameter, respectively. My derivation suggests that massive gravity could be the mechanism behind both, dark matter and dark energy.

• Journal of The Korean Astronomical Society
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• v.31 no.2
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• pp.109-115
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• 1998

We show that the low density regions of the matter distribution preserve the properties of the primordial density field better than the high density regions. We have performed a cosmological N-body simulation of large-scale structure formation in the standard CDM cosmology, and studied the evolution of statistics of under-density and over-density regions separately. The rank-order of the under-density regions is closer to the original one compared to that of the over-density regions. The under-density peaks (or voids) has moved less than over-density peaks (or dense clusters of galaxies) from their initial positions. Therefore, the under-density regions are more useful than the over-density regions in the study of the statistical property of the primordial density field.

• Journal of The Korean Astronomical Society
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• v.36 no.3
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• pp.97-103
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• 2003

We now have more than 70 multiple image gravitational lens systems. Since gravitational lensing occurs through gravitational distortions in cosmic space, cosmological informations can be extracted from multiple image systems. Specifically, Hubble constant can be determined by the time delay mea-surement, curvature of the universe can be measured by the distribution of image separations in lens systems, and limits on matter density and cosmological constant can be set by the statistics of gravitationallens systems. Uncertainties, however, still exist in various steps, and results may be taken with some caution. Larger systematic survey and better understanding of galaxy properties would definitely help.

• 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.79.4-79.4
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• 2019

We introduce a newly established cosmology research group at the University of Seoul. We also present our recent progress with SDSS Main Galaxy samples and various types of cosmological simulations as follows: (1) A hint for the periodicity of very large-scale structures is found in both SDSS observation and the Horizon Run 4 (HR4) simulation. (2) New galaxy clustering and void finding algorithms, which are thought to be sensitive to the topological shape of galaxy distribution, are developed and tested in both SDSS and HR4 data. (3) Properties such as radial distribution of galaxies or cosmological shock waves are studied in hydrodynamic simulations.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.54.1-54.1
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• 2019

We use iterative smoothing reconstruction method along with exploring in the parameter space of the light curves of the JLA supernova compilation (Joint Light-curve Analysis) to simultaneously reconstruct the expansion history of the universe as well as putting constrains on the light curve parameters without assuming any cosmological model. Our constraints on the light curve parameters of the JLA from our model-independent analysis seems to be closely in agreement with results assuming ΛCDM cosmology or using Chevallier-Polarski-Linder (CPL) parametrization for the equation of state of dark energy. This implies that there is no hidden significant feature in the data that could be neglected by cosmology model assumption. The reconstructed expansion history of the universe and properties of dark energy seems to be in good agreement with expectations of the standard ΛCDM model. Our results also indicate that the data allows a considerable flexibility for expansion history of the universe.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.58.1-58.1
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• 2021

At the University of Seoul, we are investigating the following topics in cosmology: comparing traditional clustering algorithms to our new Mulguishin algorithms, analysis of 2-body Fuzzy Dark Matter 2-body collision, 2- and 3-point clustering statistics and its dependency on the cosmological model, and dynamics of dark-matter halos around the large-scale filamentary structures. In the following sections we present a brief introduction to our studies.