• Publications of The Korean Astronomical Society
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• v.25 no.3
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• pp.91-99
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• 2010

An increasing number of observations have confirmed the presence of multiple stellar populations in Galactic globular clusters. Multiple populations evidence come from the complex chemical pattern of stars hosted in GCs and from the split or broadening of different evolutionary sequences in the color-magnitude diagrams. Multiple stellar populations have been identified in Galactic and Magellanic Cloud clusters, as well as in external galaxies. In this paper I will summarize the observational facts.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.26-26
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• 2010

Gravitationally bound objects in the universe have been a main target of astronomers for long. However, some objects in the universe may want to be free, as we do. Recently we are witnessing the existence of some globular clusters wandering in the nearby universe. The nature and origin of these wandering globular clusters are not yet known. With the advent of giant telescopes they will be an excellent tool for various fields of research including first stars, star clusters, galaxies, and galaxy clusters.

• 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.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.27.1-27.1
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• 2010

The Na-O anticorrelation seen in almost all globular clusters ever studied using high-resolution spectroscopy is now generally explained by the primordial pollution from the first generation of the intermediate-mass AGB stars to the proto-stellar clouds of the second generation of stars. Using the recent data by Carretta and his collaborators, the different shapes of the Na-O anticorrelations for RGB stars brighter than and fainter than the red giant branch bump can be clearly seen. If the elemental abundance measurements by Carretta and his collaborators are not greatly in error, this variation in the Na-O anticorrelation against luminosity indicates an internal deep mixing episode during the ascent of the low-mass RGB in globular clusters. Our result implies that the multiple stellar population division scheme solely based on [O/Fe] and [Na/Fe] ratios of a globular cluster, which is becoming popular, is not reliable for stars brighter than the RGB bump.

• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.38.1-38.1
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• 2008

Tides caused by the Galactic gravitational field affect the current dynamical structure of globular clusters in the Galaxy. Indeed, the observed feature of tidal tails stretching beyond globular clusters' tidal radii provides a key information of interaction with the gravitational field of the Galaxy and kinematical orbit of the clusters, which can be an evidence of the merging scenario of the Galaxy formation and evolution. To find such a tidal feature, we have studied spatial density distribution of stars around five globular clusters in the Galactic halo and one cluster in the Galactic bulge, for which we have used wide-field deep photometric data of gri and JHK bands obtained from the MegaCam and WIRCam of the CFHT. Applying the statistical contrast filtering of field stars in the color-magnitude plane of detected stars around five halo clusters, we have found features of tidal tails for four clusters M53, M15, NGC 5053, and NGC 5466. The detected over-density tidal features are well aligned with the cluster's orbits and stretched into the direction of the Galactic center. Statistical analysis indicate that these tidal tails are believed to be cluster stars that have escaped due to the tidal effects to the clusters. A similar tidal feature to that of halo clusters is also detected for the bulge cluster NGC 6626, while the over-density feature seems to be extended into the Galactic plane rather than into the orbital direction and the Galactic center. Conclusively, our result adds further observational evidence of the merging scenario of the Galaxy formation and evolution.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.38.2-38.2
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• 2019

S0 galaxies are mostly known to be formed in dense environments from spiral progenitors. Recently, however, a new formation scenario has been suggested that field S0s can be formed from elliptical progenitors. The Sombrero galaxy (M104, NGC 4594) is a massive disk galaxy located in the field environment, and its morphological type has been controversial from Sa to E. Thus, it is an ideal target to test the new scenario. We trace the giant halo of M104 with globular clusters to test this scenario. From the wide images obtained with CFHT/MegaCam, we find a large number of globular clusters in this galaxy. We also confirm their membership by measuring the radial velocities from the spectra obtained with MMT/Hectospec. The color distribution of these globular clusters is bimodal, and blue (metal-poor) globular clusters are more spatially widely spread than red (metal-rich) globular clusters. This indicates that M104 hosts a giant metal-poor halo as well as an inner metal-rich halo. Combining this result with the fact that M104 is unusually massive and brighter than other spiral galaxies, we infer that M104 was indeed a massive elliptical galaxy that had formed a metal-rich halo by gas-rich mergers and a metal-poor halo by gas-poor mergers. In addition, we find young star clusters around the disk of M104, which shows that the disk formed after the spheroidal halos had formed. In conclusion, we suggest that M104 was originally a massive elliptical galaxy and was transformed to a lenticular galaxy by acquiring its disk later.

• Journal of Astronomy and Space Sciences
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• v.11 no.2
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• pp.147-153
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• 1994

We present a deep(B, V) color-magnitude diagram (CMD) of the Galactic globular cluster NGC 4372. According to the recent inside-out picture of Galaxy formation, this cluster is predicted to be one of the oldest globulat clusters in the Galaxy. Our CMD shows a well defined main-sequence extending ∼ 2 magnitudes below the trunoff. Despite the uncertainty that stems from the small sample size of bright stars, comparison with the Revised Yale Isochrones suggests that this cluster may indeed be one of the oldest (∼16.6 Gyrs) globular clusters in our Galaxy.

• Journal of Astronomy and Space Sciences
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• v.21 no.3
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• pp.167-180
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• 2004

We present HST NIC3 photometry of metal-rich globular clusters Palomar 6, Liller 1 and 47 Tuc (NGC 104). We discuss the interstellar reddening law for the HST NICMOS F110W/F160W photometric system which depends on the temperature of the source. The distance moduli and interstellar reddening values for Palomar 6 and Liller 1 are estimated by comparing the magnitudes and colors of RHB stars in the clusters with those of 47 Tuc. We obtain $(m-M)_0=14.48$mag and E(B-V)=1.34mag for Palomar 6 and $(m-M)_0=15.17$mag and E(B-V)=2.50 mag for Liller 1.

• Bulletin of the Korean Space Science Society
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• 1993.10a
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• pp.18-18
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• 1993

According to the CCD photometric studies, the color distributions of globular clusters with collapsed cores, which are characterized by a power law cusp in thier surface brighness pronto, become bluer toward their centers, but this is not the case in the flat core clusters which are fit by the King model. To test the statistical implication of the color distribution within globular clusters, we built the sample dusters which follows the surface brightness pofile of the King model and power law cusp profile with the Sandage's standao luminosity function for M3 and the Salpter's initial mass functions. On the results from simulations based on the uniform random number generation the color gadients within globualr dusters mar be not likely to come from the statistical random distributions of stars but from the dynamical process on the cluster evolution.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.29.4-30
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• 2009

Extra-tidal feature of the globular clusters such as tidal tails and halos can be a crucial evidence of the merging scenario of the Galaxy formation in the dynamical point of view. To search for such an extra-tidal feature of globular clusters located in the Galactic bulge(RGC<3kpc), we obtained wide-field near-infrared JHKs images of 6 metal-poor ([Fe/H]<-1.0) clusters and 3 metal-rich ([Fe/H]>-1.0) clusters. Observations were carried out using IRSF 1.4m telescope and SIRIUS near-infrared camera, during 2006~2007. The obtained images have a total maximum field-of-view of ~ $21'\times 21'$. To select clusters' member stars and minimize the field star contaminations, we applied CMD masking algorithm. Smoothed surface density contour maps with selected stars for each cluster show overdensity features around the tidal radius and beyond. Also, radial surface density profiles within the tidal radius of the clusters show an overdensity feature as a change of slope of the radial profile. The results add further observational constraints of the formation of the Galactic bulge.