• Journal of The Korean Astronomical Society
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• v.49 no.5
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• pp.175-192
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• 2016

CCD photometric observations of the globular cluster (GC), M53 (NGC 5024), are performed using the 1.8 m telescope at the Bohyunsan Optical Astronomy Observatory in Korea on the same nights (2002 April and 2003 May) as the observations of the GC M92 (NGC 6341) reported by Cho and Lee using the same instrumental setup. The data for M53 is reduced using the same method as used for M92 by Cho and Lee, including preprocessing, point-spread function fitting photometry, and standardization etc. Therefore, M53 and M92 are on the same photometric system defined by Landolt, and the photometry of M53 and M92 is tied together as closely as possible. After complete photometric reduction, the V versus B − V , V versus V − I, and V versus B − I color-magnitude diagrams (CMDs) of M53 are produced to derive the relative ages of M53 and M92 and derive the various characteristics of its CMDs in future analysis. From the present analysis, the relative ages of M53 and M92 are derived using the Δ(B − V ) method reported by VandenBerg et al. The relative age of M53 is found to be 1.6 ± 0.85 Gyr younger than that of M92 if the absolute age of M92 is taken to be 14 Gyr. This relative age difference between M53 and M92 causes slight differences in the horizontal-branch morphology of these two GCs.

• Journal of Astronomy and Space Sciences
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• v.21 no.3
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• pp.181-190
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• 2004

We use BV CCD images to study the dynamical substructure of the globular cluster M5. We investigate the radial variation of ellipticities and position angles using the stellar photometry and the IRAF ellipse task. We find that out to three times the half light radius $(r_h)$, the changes in ellipticities and position angles range in $0.05\~0.25$ and $75^{\circ}\~-75^{\circ}$, respectively. There are no significant discrepancy in the dynamical substructure beyond $r_h$ among the different giant populations. However, compared to the global dynamical substructure of M5, the inner $(<0.5r_h)$ substructure of the bright red giant and the horizontal branch populations show slightly different patterns. Especially, the discrepancy of the bright red giant population with respect to the global substructure, ranges up to 0.1 for the ellipticity and 1000 for the position angle.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.51.2-51.2
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• 2014

Ultra faint dwarf galaxies (UFDs) are larger but fainter than globular clusters, being the faintest galaxies in the universe. They have been found only in the Local Group. We report the discovery of an UFD in the intracluster field of the Virgo cluster (Virgo UFD1). It is located near the core of Virgo cluster, and far from any massive galaxies. The color magnitude diagram of resolved stars in Virgo UFD1 shows narrow, metal poor red giant branch (RGB), which is very similar to the UFDs in the Local Group. by comparing RGB in this galaxy with 12 Gyr stellar isochrones, we estimate its distance, $d=16.4{\pm}0.4$ Mpc and mean metallicity, $[Fe/H]=-2.4{\pm}0.4$. We derive its integrated photometric properties and structural parameters : V-band absolute magnitude of $MV=-6.3{\pm}0.2$, effective radius of $84{\pm}7pc$, and central surface brightness of ${\mu}V,0=26.49{\pm}0.09$ mag arcsec-2. These properties are similar to these of Local Group UFDs. Virgo UFD1 is the first UFD discovered beyond the Local Group. These results indicate that it may be a fossil remnant of the first galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.29 no.2
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• pp.25.2-25.2
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• 2004

• The Bulletin of The Korean Astronomical Society
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• v.34 no.2
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• pp.42.1-42.1
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• 2009

• The Bulletin of The Korean Astronomical Society
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• v.28 no.2
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• pp.96-96
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• 2003

• Journal of The Korean Astronomical Society
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• v.16 no.1
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• pp.23-30
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• 1983

About two hundred stars within 50 pc from the sun, whose tangential velocity larger than 100 km/sec, have been selected on the basis of their proper motions and trigonometric parallaxes. A list of them along with their photoelectric UBV data and spectral types is given. The criterion on the tangential velocity, $v_t$ > 132 km/sec, was adopted for selection of high-velocity stars. The H-R diagram of these nearby high-velocity stars resembles that of a globular cluster, with the turnoff around $B-V{\approx}0.35$ and $M_v{\approx}4.0$, and the subdwarfs among these high-velocity stars are fainter than the main-sequence stars of Hyades by the amount of $1^m.25{\pm}0^m.30$ in the region with B-V < 1.40 on the average.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.46.2-46.2
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• 2018

Using the high-resolution observational data obtained by the Hubble Space Telescope, we found that there is the diversity of the radial trends of blue straggler stars (BSSs) in young massive clusters (YMCs) in the Large Magellanic Cloud unlike BSSs in old globular clusters usually showing the segregated radial distributions. To understand the dynamical processes that lead to the none-segregated or even inversely-segregated radial distribution of BSSs, we performed direct N-body simulations for YMCs. Our numerical simulations show that the presence of black hole subsystems inside the cluster centre can significantly affect the dynamical evolution of BSSs and eventually lead to none- or inversely-segregated radial distribution of BSSs.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.48.1-48.1
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• 2019

Mass and radius of a neutron star in low-mass X-ray binary (LMXB) can be estimated simultaneously when the observed light curve and spectrum show the photospheric radius expansion feature. This method has been applied to 4U 1746-37 and the mass and radius were found to be unusually small in comparison with typical neutron stars. We re-estimate the mass and radius of this target by considering that the observed light curve and spectrum can be affected by other X-ray sources because this LMXB belongs to a very crowded globular cluster NGC 6441. The new estimation increases the mass and radius but they do not reach the typical values yet.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.52.2-52.2
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• 2010

In search of the intracluster dusts, we have made a survey of globular clusters (GCs) with the Far-Infrared Surveyor (FIS) aboard AKARI, the Japanese infrared space satellite. The GCs are thought to host dust particles that are condensed from the material injected by the cluster asymptotic giant branch (AGB) stars. However, attempts to detect dust emission from GCs had not been successful until a significant amount of far-infrared (FIR) emission was detected close to the NGC 7078 center by the ISO observations (Evans et al. 2003). Recent FIR observations by the AKARI (Matsunaga et al. 2008) and the Spitzer Space Telescope (Boyer et al. 2006; Barmpy et al. 2009) reported a tentative detection of the dusts in NGC 5024 and NGC 6341, and also confirmed the previous ISO dust detection from NGC 7078. We have observed 17 selected GCs in four FIS wavebands at 65, 90, 140, and 160 micrometers. Each observation covers about $10'{\times}10'$ area centered at each GC. The resulting images show extended structures and/or blobs around the GCs. The extended structures are very suggestive of the Galactic cirrus, while the blobs around NGC 288 and NGC 4833 seem to be related to the two clusters. In this presentation, we will report four representative cases of our survey results and discuss the properties of newly detected sources.