• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.64.2-64.2
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• 2013

As more spectroscopic observations accumulate, it becomes evident that there are variations in light elements, such as C, N, O, and Na, between the sub-populations in most globular clusters (GC) in the Milky Way. We have constructed a new set of isochrones and horizontal branch evolutionary tracks with enhanced Nitrogen and depleted Oxygen to study their effects on the evolution of stars in GCs. From these results, we found that their effects on the evolution in color-magnitude diagram are significant in determining the age of GCs. In order to reflect these effects in the construction of population models for GCs, we have expanded the parameter space of Yonsei-Yale Isochrones and HB evolutionary tracks by introducing abundance enhancements of N for various global metal abundances and helium contents. In this paper, we will present our preliminary results from these calculations.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.74.1-74.1
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• 2013

We have performed new narrow-band calcium photometry for Milky Way globular clusters (GCs) and detected multiple red giant branches (RGBs) in some massive GCs. Our new calcium filter was designed to avoid the CN contamination below $3883{\AA}$ and to measure only Ca II H&K lines. The fact that we are detecting multiple RGBs from the new filter is suggesting that they are indeed different in calcium abundance, which can only be produced by supernovae (SNe). Therefore, the presence of the multiple RGBs for the peculiar GCs in the calcium photometry is best understood if the later generation of stars are enhanced in some SNe products. In this talk, we will present our progress in the calcium photometry for the peculiar GCs showing the multiple RGBs.

• Journal of Astronomy and Space Sciences
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• v.17 no.1
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• pp.33-38
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• 2000

Synchrotron emission at 408 MHz and HI column density have been used to find an evidence for the relationship between the Galactic magnetic field and the gas density. The observational data of the brightness temperature and HI column density, $T_b(408)\;and \;N_{HI}$, near the galactic plane between galactic longitudes $l=62^{circ}\;and\;l=250^{\circ}$ show a clear linear correlation of $T_b(408)=A(l,b)+B\;N_{HI}$, where A(l, b)is a background and forground radiation at the galactic coordinate. We found $(1.4{pm}0.3)10^{-21}$ for the slope B, which describes the strength of the syncrotron radiation from the HI cloud, and agrees with the value for the MIlky Way obtained by Beuermann et al. (1985). We conclude therefore that a well defined nonthermal corelates with the HI column density originating from this HI cloud.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.79.2-79.2
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• 2014

Galactic radio pulsar population is diverse. So far about 2300 radio pulsars are known in the Milky Way, in addition to Large and Small Magellanic Clouds. Radio pulsar observations at a few hundreds MHz up to ~10 GHz have been active and they are proved to be fruitful. Low frequencies are preferred mainly because of the steep ratio spectrum of pulsars. However, developments in pulsar backends (e.g. a wide-band spectrometer) and improved system sensitivities make it possible to observe pulsars at higher frequencies using large, single-dish telescopes up to ~18 GHz. Going forward, mm-wavelength observations is expected to open a new window in pulsar astronomy. In particular, frequencies well above ~15 GHz are pre-requisite to detect pulsars in the Galactic Center where radio pulsed signals are severely scattered by interactions with the interstellar medium. Recent discoveries strongly imply that there are subsets of pulsars with an apparently flat spectrum, such as magnetars. In April 2014, the first pulsar (magnetar) was discovered only 3 arcmin from Sgr A*, PSR J1745-2900. We will present a brief overview on pulsar populations focusing on those observable at high frequencies. We will also discuss prospects of pulsar observations in mm-wavelengths and how we can utilize the Korean VLBI network.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.53.3-54
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• 2016

We combine a semi-analytic model of galaxy evolution with constraints on circumstellar habitable zones and the distribution of terrestrial planets in order to probe the suitability of galaxies of different mass and type to host habitable planets, and how it evolves with time. We find that the fraction of stars with terrestrial planets in their habitable zone (known as habitability) depends only weakly on galaxy mass, with a maximum around $4{\times}10^{10}M_{\odot}$. We estimate that 0.7% of all stars in Milky Way-type galaxies to host a terrestrial planet within their habitable zone, consistent with the value derived from Kepler observations. On the other hand, the habitability of passive galaxies is slightly but systematically higher, unless we assume an unrealistically high sensitivity of planets to supernovae. We find that the overall habitability of galaxies has not changed significantly in the last ~8 Gyr, with most of the habitable planets in local disk galaxies having formed ~1.5 Gyr before our own solar system. Finally, we expect that ${\sim}1.4{\times}10^9$ planets similar to present-day Earth have existed so far in our galaxy.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.59.1-59.1
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• 2016

Blue Straggler Stars(BSS) affect their host star cluster in various parameters like color, dynamics, etc. For this reason, it is important to know how to relate BSS frequency and evolution of their host stellar system. To statistical study about global properties of open clusters as the environments of BSS formation, we use three catalogues - (1) two galactic open clusters catalogues including BSS candidate, (2) Milky Way Star Cluster (MWSC) survey data. Then, we compare with the data of two BSS catalogues for test of the result of Marchi et al. 2006. We also investigate the radial mass distribution in open cluster, because it is possible that changing the gradient of radial mass distribution cause increasing the BSS frequency. When we group the open cluster into having BSS or not and other criteria, the groups show slight discrepancies, but we show some important results.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.40.3-41
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• 2016

Previous HI survey data have shown that the central HI gas in the Milky Way that resides within ~1.5 kpc of the Galactic Centre (GC) is tilted by ${\sim}15^{\circ}$ with respect to the Galactic plane. Although several models, such as a tilted disk model, have been suggested to interpret the observed morphology of the HI layer, it is still unknown what causes and how it preserves its tilted structure. We study the behavior of a gas disk near the GC using an N-body / SPH code. Our galaxy model includes four components; nuclear bulge, bulge, disk and halo. We construct a HI model whose radius is 1.3 kpc, scale height is 100 pc and mass is $3.6{\times}10^6M_{\odot}$. We also assume that the gas disk is initially tilted $30^{\circ}$ with respect to the Galactic plane. Here we report our simulation results and discuss the evolution of the tilted gas disk.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.129-131
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• 1996

The results on the deep low dispersion (1250 ${\AA}$/mm at $H_r, $30^{\circ}$ < I < $165^{\circ}$, $195^{\circ}$ < I < $210^{\circ}$, [b] < $5^{\circ}$; 7000${\AA}$/mm at A band, $50^{\circ}$ < I < $115^{\circ}$, b=$0^{\circ}$, b=${\pm}3.5^{\circ}$) spectral surveys of the MILKY WAY are presented. More than 2250 carbon stars were identified among them 1440 new ones. The C/M5+ ratio increases from 0.02 to 0.3 when longitude varies from $30^{\circ}$ to $210^{\circ}$. On the basis of A GENERAL CATALOG OF GALACTIC COOL CARBON STARS the surface distribution of carbon stars has been studied.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.80.2-80.2
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• 2017

We present chemical and kinematic properties of the Milky Way's halo system investigated by carbon-enhanced metal-poor (CEMP) stars identified from the Sloan Digital Sky Survey. We first map out fractions of CEMP-no stars (those having no over-abundances of neutron-capture elements) and CEMP-s stars (those with over-enhancements of the s-process elements) in the inner- and outer-halo populations, separated by their spatial distribution of carbonicity ([C/Fe]). Among CEMP stars, the CEMP-no and CEMP-s objects are classified by different levels of absolute carbon abundances, A(C). We investigate characteristics of rotation velocity and orbital eccentric for these subclasses for each halo population. Any distinct kinematic features identified between the two categories in each halo region provide important clues on the origin of the dichotomy of the Galactic halo.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.78.4-79
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• 2017

Thermal inflation is an additional inflationary mechanism before the big bang nucleosynthesis, which solves the moduli problem and naturally provides a plausible dark matter candidate. Thermal inflation leaves a slight enhancement followed by huge suppression of a factor of ~50 in the curvature and matter power spectrum, which can be expressed in terms of a single characteristic scale $k_b$. Here we describe the observability of the small-scale features of thermal inflation from various observations, such as CMB distortion, satellite galaxy abundance in the Milky-Way-sized galaxies, and 21-cm power spectrum before the epoch of reionization.