• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.78.1-78.1
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• 2013

The hierarchical model of galaxy formation predicts that galaxy halos contain merger relics in the form of long stellar stream. Thus, tidal substructure of stars around globular clusters, such as tidal tails, could be an essential evidence of the merging scenario in the formation of the Galaxy. From April 2010 to December 2012, we obtained $45^{\prime}{\times}45^{\prime}$ wide-field JHKs near-infrared photometric imaging data for about 20 globular clusters in the Milky Way, and examined the stellar density distribution around globular clusters. Here, we introduce the preliminary results of stellar spatial distributions and radial surface density profiles of four globular clusters. In order to minimize the field star contamination and identify the cluster's member candidates stars, we used a statistical filtering algorithm and gave weights on the CMDs of globular clusters. In two-dimensional stellar density maps, we could found tidal stripping structures for some globular clusters. The orientation of tidal substructure seems to associate with the effects of dynamical interactions with the Galaxy and cluster's orbit. Indeed, the radial surface density profile accurately describes this stripping structures as a break in the slope of profile. The observational results could give us further observational evidence of merging scenario of the formation of the Galaxy.

• Journal of The Korean Astronomical Society
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• v.31 no.2
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• pp.127-140
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• 1998

With a large format near-infrared camera at the 2.2-m telescope on Mauna Kea Observatory, we performed J K near-infrared observations for the metal rich globular cluster NGC6712. This cluster lies near the galactic plane and therefore suffers heavy reddening. We present the near-infrared color-magnitude diagram and also derive the metallicity ([Fe/H] ${\~}-0.96{\pm}0.27$) as well as its distance modulus ((m - M) ${\~}13.42{\pm}0.12$).

• Journal of The Korean Astronomical Society
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• v.46 no.4
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• pp.173-181
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• 2013

We trace the dynamical evolution of dark matter (DM) content in NGC 6397, one of the native Galactic globular clusters (GCs). The relatively strong tidal field (Galactocentric radius of ~ 6 kpc) and short relaxation timescale (~0.3 Gyr) of the cluster can cause a significant amount of DM particles to evaporate from the cluster in the Hubble time. Thus, the cluster can initially contain a non-negligible amount of DM. Using the most advanced Fokker-Planck (FP) method, we calculate the dynamical evolution of GCs for numerous initial conditions to determine the maximum initial DM content in NGC 6397 that matches the present-day brightness and velocity dispersion profiles of the cluster. We find that the maximum allowed initial DM mass is slightly less than the initial stellar mass in the cluster. Our findings imply that NGC 6397 did not initially contain a significant amount of DM, and is similar to that of NGC 2419, the remotest and the most massive Galactic GC.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.49.1-49.1
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• 2012

Recently it is found that the globular clusters are not only bound in their host galaxies, but also are wandering between galaxies in Virgo and Coma clusters. The cluster-wide distribution of these intracluster globular clusters (IGCs) suggests that IGCs are an important probe to understand hierarchical structure formation. We present a survey of IGCs in Virgo cluster using HST archive images for four HST/ACS fields located from about 9 arcmin to 40 acrmin from the cluster center. We find ten new IGCs and confirm four previously known IGCs. The number density of IGCs decreases as the distance from the cluster center increases. We derive integrated photometry of IGCs. We also obtain photometry of resolved stars in the outer region of each cluster. These IGCs are fainter than $M_V{\approx}-9.5$ and mostly blue in (V-I) color. showing that they are mostly metal poor. The locations of red giant branch stars of IGCs in color-magnitude diagrams also show that they are meal-poor. We discuss the implications of these results.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.82.1-82.1
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• 2010

We have investigated the spatial configuration of stars within the tidal radius of metal poor globular cluster NGC 6626 in the bulge direction. Data were obtained in near-IR J,H,Ks bands with wide-field ($20'\times20'$) detector, WIRCam at CFHT. To trace the stellar density around target cluster, we sorted cluster's member stars by using a mask filtering algorithm and weighting the stars on the color-magnitude diagram. From the weighted surface density map, we found that the stellar spatial distributions within the tidal radius appear asymmetric and distorted features. Especially, we found that more prominent over-density features are extending toward the direction of Galactic plane rather than toward the directions of the Galactic center and its orbital motion. This orientation of the stellar density distribution can be interpreted with result of disk-shock effect of the Galaxy that the cluster had been experienced. Indeed, this over-density feature are well represented in the radial surface density profile for different angular sections. As one of the metal poor globular clusters with extended horizontal branch (EHB) in the bulge direction, NGC 6626 is kinematically decoupled from the normal clusters and known to have disk motion of peculiar motion. Thus, our result will be able to add further constraints to understand the origin of this cluster and the formation of bulge region in early universe.

• Journal of Astronomy and Space Sciences
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• v.13 no.1
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• pp.55-62
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• 1996

We present UBV CCD photomety of the metal-poor globular cluster M30. The data were obtained using the 40 inch telescope at Mt. Stromlo and Siding Spring Observatory (MSSSO). We used DAOPHOT CCD reduction package in order to obtain Color-Magnitude Diagram (CMD). We have derived some fundametal parameters of the globular cluster such as metal abundance ([Fe/H]), helium abundance (Y), and distance modulus (m-M) from the CMD. The derived parameters were [Fe/H]=-2.50, Y=0.28, and (m-M)=14.64. From the latter, the distance of 8.3kpc is obtained. Despite the photometric uncertainty near the main-sequence turnoff, we estimate the age of M30 to be 1.6${\pm}$3 Gyrs from the Revised Yale Isocyrones. If [O/Fe]=+0.4, this age will be reduced to 14.2${\pm}$3 Gyrs.

• Journal of Astronomy and Space Sciences
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• v.14 no.2
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• pp.194-201
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• 1997

We have carried out JK near-infrared photometry for the central region of the metal rich globular cluster M71, whose (K, J - K) color-magnitude diagram is presented here. Using two independent methods we derive the distance modulus to M71, 12.89 and 12.86 $pm0.12$ respectively. The former is derived using the HB luminosity $M_{Ko}$(HB) = -1.15 for globular clusters having metallicity between -1.0 to -0.3 (Kuchinski et al. 1995). The latter is derived through a comparison with IR photometry of stars in the similar metallicity cluster 47 Tuc. We also estimate the reddening to M71, E(J - K) = 0.13, based on E(B - V) = 0.04 of 47 Tuc.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.33.1-33.1
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• 2015

M85 is a nearby merger remnant galaxy located at the northern part of the Virgo Cluster. Because of its remarkable merging features, it is an interesting object to investigate its formation history. Globular clusters are a great tracer of the formation history of early-type galaxies, so that we study the globular cluster system of M85. It has been already found that there are "intermediate-color" globular clusters as well as blue and red ones based on the photometric survey using CFHT/Megacam. For follow-up research, we obtain the spectra of 21 globular clusters in the central region of M85 using Gemini-N/GMOS. We estimate their ages and metallicities based on the strength of Lick indices. We detect the intermediate-age population (~ 2 Gyr) with solar metallicities, comprising about 50% of the observed globular clusters, as well as old and metal-poor population. It suggests that M85 experienced a major merging event around 2 Gyr ago. We discuss these results regarding to the formation history of M85.

• Publications of The Korean Astronomical Society
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• v.15 no.spc1
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• pp.1-13
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• 2000

We review the early historical developement of astronomical spectrographs, properties of emission line spectra of HII regions in spiral galaxies, and absorption line features of galactic globular clusters. Emission line spectra of HII regions within three spiral galaxies NGC 300, NGC 1365, and NGC 7793, which were observed from AAT/IPCS, had been analysed, and we discuss the abundances of elements in HII regions and the radial abundace gradients through the galaxies. The radial UBV color variations of two globular clusters, NGC 1851 and NGC 2808, were examined for correlations with radial variations of several absorption lines in the integrated spectra, which were obtained from SAAO 74 inch telescope and image tube spectrograph. Nine giant star's spectra in NGC 3201 were also obtained and analysed for the radial abundance gradients in the globular cluster. The results show that the presence of a radial color gradient in a globular cluster is correlated with the presence of abundance gradients. Finally, we suggest some scientific programs for the new high dispersion spectrograph, which will be installed to the BOAO 1.8m telescope.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.30.3-31
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• 2016

The M81 Group is the nearest among the known groups of galaxies. HI maps show that all main galaxies of this group are interacting, indicating that this group is in the active phase of formation. On the other hand, wide field imaging shows that globular cluster candidates are found not only in the member galaxies but also between the galaxies in this group. In this study we present preliminary results based on MMT/Hectospec spectroscopy of the globular cluster candidates in this group. We find that the intragroup globular clusters have mostly low metallicity, while the globular clusters in M81 have mostly high metallicity. We will discuss the implication of this result and the kinematics of the globular clusters in relation with the formation history of the M81 Group.