• Journal of Astronomy and Space Sciences
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• v.7 no.2
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• pp.125-139
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• 1990

Luminosity profiles and dynamical parameters of 12 globular clusters in the Large Magellanic Cloud(SB(s)m) are obtained from the concentric aperture photoelectric photometry of 3 different aged clusters and the collected photometric data of 9 clusters. The total masses of the globular clusters are calculated using the equation $M_\bigoplus$= ${Mr_t}^j(4\Omega^2-k^2)$, which is derived from the theroetical rotation curve for the exponential disk(Chun 1978). These masses lie between $0.3\times10^4$ and $15.8\times10^4M_\bigoplus$. From the determined total mass and luminosity, the mass-to-luminosity ratios are also derived. The M/L ratio of a cluster increases with the cluster age ; about 0.03 for the youngest clusters(SWB I) and about 0.24 for the oldest clusters (SWB VII). There is a difference in M/L by a factor of 10 between the galactic globular clusters and the old globular clusters in the LMC.

• Bulletin of the Korean Space Science Society
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• 2004.10b
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• pp.321-324
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• 2004

We used BV CCD images to study the dynamical substructures of three globular clusters - M5, NGC6934, NGC7006 - analyzing the radial variations of ellipticity and position angle from the point spread function stellar photometry and the ellipse surface photometry. Several populations were classified by the brightness on color-magnitude diagrams of each globular cluster. Ellipse analyses to the images, removed stars of each population from the original images of the clusters, show radial variations in ellipticity and position angle, with the amount of $0.01\~0.25$ in ellipticity and $+90\~-90$ degrees in position angle up to roughly three times of half light radius $(r_h)$. It is also apparent that there are no significant discrepancies in the dynamical substructures beyond $r_h$ among the different populations. However, dynamical substructures on the central region (i.e., inner than $\~r_h$) reflect the contributions of populations of bright red giant stars and horizontal branch stars.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.34.1-34.1
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• 2015

Deep archival V and I image data taken with Hubble Space Telescope have been used to investigate compact stellar objects in an anemic spiral galaxy NGC 4921 in the Coma cluster. We resolve a significant fraction of globular clusters based on the reconstructed master drizzled image data. The color distribution of globular clusters (GCs) shows a clear bimodal distribution. The blue and red GC populations show significantly different radial number density profiles. We derive the turnover magnitudes of globular cluster luminosity functions (GCLFs) for the blue and red GCs in the bulge and halo of NGC 4921. We also derive the GCLFs of two Coma cD galaxies, NGC 4874 and NGC 4889, and one coma S0 galaxy, NGC 4923. Turnover magnitudes of GCs in four galaxies agree well within uncertainties. A mean distance of four Coma galaxies is derived from turnover magnitudes of GCLFs. A value of the Hubble constant is determined from this distance estimate and radial velocity of the Coma. We discuss implications of our results in relation with the recent determinations of the Hubble constant.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.53.1-53.1
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• 2014

The M81 group is a nearby galaxy group hosted by M81, a twin galaxy of Milky Way. This galaxy group is considered as an ideal laboratory for near-field cosmology to understand mass assembly and evolution of galaxies in the group environment. We designed a project to investigate spectroscopic properties of globular cluster candidates in this group. We obtained spectra of globular cluster candidates using the MMT/Hectospec as a part of the K-GMT Science Program. Our main targets include globular cluster candidates of the M81 group member galaxies and those wandering in the intragroup region. We also observed supernova remnants and some background galaxies. Observing fields covered about 2 square degrees including three main galaxies of the M81 group. Using these spectra, we will identify globular clusters in the M81 group, and investigate their properties including age and metallicity. We will discuss the MMT/Hectospec data reduction processes, and future plan for this project.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.27.1-27.1
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• 2010

Globular cluster (GC) systems in most galaxies, particularly in ellipticals, show bimodal color distributions. Because broadband colors trace metallicity at old ages, this phenomenon has been commonly interpreted as bimodal metallicity distributions, implying the presence of two sub-populations in the globular cluster system within a galaxy. However, a new explanation has recently been proposed, in which the non-linear nature of color-metallicity relations induced by horizontal-branch stars can produce bimodal color distributions even from unimodal metallicity distributions. In this study, we put these two explanations to the test on the origin of color bimodality, using multi-band (U,B,V and I) photometry of globular clusters in NGC 1399, the central giant elliptical galaxy in Fornax galaxy cluster. We find significant changes in the morphology of color distributions when using different colors. The observation is also well reproduced by the Monte Carlo realization of GC color when a unimodal metallicity distribution and the theoretical non-linear color-metallicity relations are assumed. We discuss the implications regarding theories on galaxy formation and evolution.

• Bulletin of the Korean Space Science Society
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• 2001.11a
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• pp.16-16
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• 2001

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.80-80
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• 2014

Dynamics of a globular cluster (GC) is dominated by behaviors of high-mass components such as neutron stars or black holes (BHs). Massive components in a cluster are segregated into the cluster core and some of them are ejected by dynamical interactions. In this study, we perform N-body simulations of GCs adapting two BH mass components, $10M_{\odot}$ and $20M_{\odot}$. Previous studies which mostly assume single-mass BHs suggested a rapid collapsing and escaping of BHs. A cluster with a two-component BH mass spectrum, however, retains a large fraction of $10M_{\odot}$ BHs longer. In addition to their roles in cluster dynamics, massive components in binaries are one of important sources of gravitational waves (GWs). We investigate properties of BH binaries escaped from the cluster and discuss their implications for GW detection.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.29.2-29.2
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• 2009

During the last four years, we have performed Sejong/ARCSEC Ca uvby survey using the CTIO-1m telescope aimed at obtaining Ca uvby photometry for about 50 globular clusters and selected fields in Baade's Windows. Our results show that Ca uvby photometric system can provide a powerful method to probe multiple populations in Galactic globular clusters. We will discuss the multiple stellar population in the globular cluster NGC6218 and NGC6752 as illustrations.

• Journal of The Korean Astronomical Society
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• v.46 no.6
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• pp.203-224
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• 2013

Wide-field $JHK_s$ images obtained with the SIRIUS near-infrared camera of the IRSF 1.4m telescope are used to examine the tidal structures of the spatial stellar configuration around six metal-poor ([Fe/H]< -1.0) globular clusters located within 3 kpc from the Galactic center. The radial surface density profiles are obtained from the surface photometry of the cluster images and the star counting for the photometric data. For the star counting, candidates of cluster member stars are selected with an filtering algorithm in color-magnitude diagrams. We find that the six target clusters show tidal overdensity features in the radial surface density profiles. There is a break inside the tidal radius for each cluster, and the profile in the outer overdensity region is characterized by a power law. Two-dimensional density maps of all the clusters show distorted asymmetric stellar configurations in the outer region. In five out of the six target clusters, the overdensity features are likely to be associated with the effects of the Galaxy dynamical interaction and the cluster space motions. The observed tidal configurations of stars suggest that several metal-poor clusters in the Galactic bulge are possibly surviving remnants of mergers to build the old stellar system of the Galactic bulge.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.30.2-30.2
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• 2015

Abell 2744 is a giant merging cluster, called the Pandora's Cluster, at the redshift of z=0.308 (corresponding to a distance of 1270 Mpc). Taking the advantage of the deep high resolution images in the Hubble Frontier Field program, we study the properties of compact stellar systems including globular clusters and ultracompact dwarfs (UCDs) as well as dwarf galaxies in this cluster. We find a rich population of globular clusters and UCDs in Abell 2744. The spatial distribution of these objects is consistent with the mass map derived from lensing analysis, while showing a significant offset from the X-ray map of hot gas. The faint end of the luminosity function of the galaxies in the red sequence is fit by a flat slope, showing no faint upturn. We discuss these finding in relation with the origin of UCDs, formation of red sequence dwarf galaxies, and formation of the Pandora's cluster.