• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.73.1-73.1
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• 2013

It is believed that the current census of star clusters in the Milky Way is far from being complete, because of high extinction. Taking advantage of recent wide-field infrared surveys (the WISE as well as 2MASS, UKIDSS GPS, and VVV), we search for new star clusters in the central region of the Milky Way (720 $deg^2$-wide area at |1| < $30^{\circ}$ and |b| < $6^{\circ}$). We find 1840 candidates by visual inspection of the WISE images. The spatial distribution of these candidates show a strong concentration along the Milky Way, showing that most of them belong to the Milky Way. Among them, 26 are probably star clusters, considering their morphology, color-magnitude diagrams, and the degree of central concentration of stars. Eighteen of them appear to be very young in the embedded phase, and six of them are considered to be relatively old, showing a developed red giant branch. Implications of the primary results will be discussed.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.46.1-46.1
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• 2013

High velocity clouds (HVCs) are H I clouds that move with large speed (${\mid}V_{LSR}{\mid}$ >100 km/s) in the halo of the Milky Way. It is now evident that at least some populations of HVCs originated from extragalactic sources, either primordial gas left over from the galaxy formation or gaseous material stripped off from other galaxies closely passing by the Milky Way. HVCs with extragalactic origin play an important role in the star formation of the Milky Way when they eventually collide with the disk of the Milky Way. Although it is still observationally controversial whether HVCs are surrounded by dark matter or not, it is theoretically interesting to investigate the effect of dark matter on the collision of HVCs with the disk of the Milky Way. We model this scenario by using hydrodynamic simulations and search for proper parameters that explain the currently available observations such as the Smith Cloud that is thought to have collided with the Galactic disk already.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.84.2-84.2
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• 2014

We report the discovery of a new Milky Way globular cluster (GC) candidate in the Galactic plane. We found this object during our WISE survey of star clusters in the Milky Way. We derived physical parameters of this object using the 2MASS JHK photometry. The color-magnitude diagram of the resolved stars shows a well-developed red giant branch (RGB). We derived its reddening, distance and metallicity. These results indicate that it is probably an old globular cluster, located behind the Galactic disk.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.36.1-36.1
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• 2017

A major goal of the proposed Korean Neutrino Detector and Telescope is to detect neutrino burst from core-collapse supernova (SN) explosions in the Milky Way, which will provide an unprecedented opportunity to look into the core of an exploding massive star. Detection with high statistics would give important information for the explosion physics. It can also detect neutrino signals from SN events in the Local Group and trigger alert of the event for the astronomical community. In this talk, I will review the SN rates of the Milky Way and the Local Group, and will discuss the implications for the proposed neutrino telescope.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.77.2-77.2
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• 2014

Questions of how our Milky Way evolves through the interaction with its environment have been constantly raised. One particularly interesting question is how the metallicity would change as our Milky Way goes through collision with HVCs. Because of the possibility of HVCs providing fuel for star formation in the Galactic disk, we simulate the collision between HVCs and the Galactic disk. More specifically, we trace how the Galactic metallicity changes throughout the process of HVCs colliding with our Milky Way based upon a specific scenario that HVCs are primordial gas left-overs from an ancient galaxy formation. Such mixing between metal-rich gas (disk) and metal-poor HVC can be traced by running numerical simulations with the FLASH code due to its capability of tracking down the abundance change of a specific element such as carbon at each time step of the hydrodynamic evolution. As for now, we give how this mixing depends on model parameters that we choose such as collision speed, initial metallicities, temperature and so on.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.57.2-57.2
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• 2012

We present a survey for finding hidden star clusters using the WISE data. There are more than two thousand star clusters in the current catalogs of star clusters in the Milky Way Galaxy. However, there are still numerous star clusters remaining to be discovered, especially, along the Milky Way. The WISE, NIR to MIR all sky survey, is an efficient source to find star clusters obscured by dust along the Milky Way. Taking the advantage of the power of WISE, we survey a wide area at ${\mid}l{\mid}<30^{\circ}$ and ${\mid}b{\mid}<6^{\circ}$, toward to the central region of the Milky Way to find new star clusters. To find cluster candidates, we used two kinds of method: the visual inspection and the brightness density investigation. We will report the progress of this survey.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.57.3-57.3
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• 2015

The formation of the Milky Way stellar halo is thought to be the result of merging and accretion of building blocks such as dwarf galaxies and massive globular clusters. Recently, Deason et al. (2015) suggested that the Milky Way outer halo formed mostly from big building blocks, such as dwarf spheroidal galaxies, based on the similar number ratio of blue straggler (BS) stars to blue horizontal-branch (BHB) stars. Here we demonstrate, however, that this result is seriously biased by not taking into detailed consideration on the formation mechanism of BHB stars from helium enhanced second-generation population. In particular, the high BS-to-BHB ratio observed in the outer halo fields is most likely due to a small number of BHB stars provided by GCs rather than to a large number of BS stars. This is supported by our dynamical evolution model of GCs which shows preferential removal of first generation stars in GCs. Moreover, there are sufficient number of outer halo GCs which show very high BS-to-BHB ratio. Therefore, the BS-to-BHB number ratio is not a good indicator to use in arguing that more massive dwarf galaxies are the main building blocks of the Milky Way outer halo. Several lines of evidence still suggest that GCs can contribute a signicant fraction of the outer halo stars.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.78.1-78.1
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• 2015

Recent studies for the Milky Way globular clusters (GCs) have reported that most of them host multiple stellar populations. However, only a few GCs have shown abundance variations in heavy elements such as iron and calcium. These GCs, as galaxy building blocks, are important to understand the formation of the Milky Way in hierarchical merging paradigm. In this study, we report our discovery from the Ca narrow-band photometry and low-resolution spectroscopy that NGC 6273 is a new Milky Way building block candidate.

• 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.35 no.1
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• pp.56.2-56.2
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• 2010

M87, a cD galaxy in the Virgo cluster, has 3-10 times larger enclosed mass than the Milky Way at any given galactocentric radius. Thus the globular cluster (GC) system in M87 is expected to have undergone a more significant dynamical evolution than that of the Milky Way if it had started from the same initial mass function (MF) and radial distribution (RD) as the Milky Way. The evolution of MF and RD of the M87 GC system has been calculated using an advanced, realistic Fokker-Planck (FP) model that considers dynamical friction, disk/bulge shocks, and eccentric cluster orbits. We perform hundreds of FP calculations with different initial cluster conditions, and then search a wide parameter space for the best-fit initial GC MF and RD that evolves into the observed present-day GC MF and RD. We also find best-fit initial MFs and RDs for blue and red GC groups, separately.