• Journal of The Korean Astronomical Society
• /
• v.29 no.2
• /
• pp.157-170
• /
• 1996

In order to determine the metallicity of a globuar cluster, M3,by using the spectral indices, a kind of index grid has been establshed by stars in globular clusters, M3, M15, M71 and old open cluster, NGC 188. The indices were measured from the medium resolution spectra of about $2{\AA}$. The summed indices were used to determine metallicity in order to increase signals. It is found that the core depth index is measured more accurately and leads result more accurate than the pseudo-equivalent width index. This method can be further improved by including many more calibration globular clusters of various metallicity to make finer grids. By this method, the metallicity of M3 is determined as $[Fe/H] = -1.46\pm0.15$.

• Journal of Astronomy and Space Sciences
• /
• v.18 no.1
• /
• pp.7-14
• /
• 2001

Red giant branch shape and the luminosity of horizontal branch on the (V-I)-V CMD are used to derive the metallicity the globular cluster NGC 5053. The metallicities of NGC 5053 derived by SMR method ([Fe/H]=-2.62$\pm$0.07) and the relation between[Fe/H] and $(V-I)_{0.g}$ ([Fe/H]=-2.50) are in good agreement with previously determined values. This result confirms that the morphologies of RGB and HB on the (V-I)-V CMDs can be good indirect photometric metallicity indicators of galactic globular clusters.

• The Bulletin of The Korean Astronomical Society
• /
• v.38 no.1
• /
• pp.57.2-57.2
• /
• 2013

Based on N-body simulations, we find out that significant fraction of dynamically formed BH-BH (10 $M_{\odot}$ and NS-NS (1.4 $M_{\odot$ ecah) binaries are ejected from globular clusters. About 30 percent of compact stars are ejected in the form of binary. The merging time of ejected binary depends on the velocity dispersion of globular cluster. Some of ejected binaries have merging time-scales shorter than Hubble time and are expected to produce gravitational waves that can be detectable by the advanced ground-based interferometers. The merger rates of ejected BH-BH and NS-NS binaries per globular cluster are estimated to be 3.5 and 17 per Gyr, respectively. Assuming the spatial density of globular clusters as 8.4 $h^3$ clusters $Mpc^{-3}$ and extrapolating to the horizon distance of the advanced LIGO-Virgo network, we expect the detection rates solely attributed to BH-BH and NS-NS with cluster origin are to be 42 and 1.7 $yr^{-1}$, respectively. Besides, we find out that BH-NS binary ejection hardly occurs in globular clusters and dynamically formed compact binaries may possibly be the source of short GRBs whose locations are far from host galaxies.

• Journal of The Korean Astronomical Society
• /
• v.29 no.spc1
• /
• pp.137-138
• /
• 1996

The first large-format CCD color-magnitude diagram (CMD) in the B and V passbands is presented for the Galactic globular cluster M53 (NGC 5024). We have discovered 117 new blue straggler (BS) candidates in the field of M53. The analysis of bright BS stars (V <19.0) clearly shows a bimodal radial distribution, with a high frequency in the inner and outer regions. The distribution is similar to that found in M3, a globular cluster with similar central density and concentration.

• Journal of The Korean Astronomical Society
• /
• v.14 no.1
• /
• pp.13-17
• /
• 1981

The observed radial UBV colour variations (both B-V and U-B) of some globular clusters are examined for correlations with radial variations in the integrated spectra. The results show that the presence of a radial colour gradient is correlated with the presence of a gradient of the CN (and possibly the G-band) line strength, in the sense that the CN (and possibly the G-band) is stronger in the centre (where the cluster is redder) and becomes weaker in the outer region of the cluster (where the cluster is bluer). This may suggest that a primordial abundance, possibly nitrogen and carbon gradient was set up in the early stage of cluster formation.

• The Bulletin of The Korean Astronomical Society
• /
• v.38 no.2
• /
• pp.76-76
• /
• 2013

The current hierarchical model of galaxy formation predicts that galaxy halos contain merger relics in the form of long stellar streams. In order to find stellar substructures in galaxy, we focused our investigation on the stellar spatial density around globular clusters and on the quantitative properties of the evolved sequences in the color-magnitude diagrams (CMDs). First, we investigated the spatial configuration of stars around five metal-poor globular clusters in halo region (M15, M30, M53, NGC 5053, and NGC 5466) and one metal-poor globular cluster in bulge region (NGC 6626). Our findings indicate that all of these globular clusters show strong evidence of extratidal features in the form of extended tidal tails around the clusters. The orientations of the extratidal features show the signatures of tidal tails tracing the clusters' orbits and the effects of dynamical interactions with the galaxy. These features were also confirmed by the radial surface density profiles and azimuthal number density profiles. Our results suggest that these six globular clusters are potentially associated with the satellite galaxies merged into the Milky Way. Second, we derived the morphological parameters of the red giant branch (RGB) from the near-infrared CMDs of 12 metal-poor globular clusters in the Galactic bulge. The photometric RGB shape indices such as colors at fixed magnitudes, magnitudes at fixed colors, and the RGB slope were measured for each cluster. The magnitudes of the RGB bump and tip were also estimated. The derived RGB parameters were used to examine the overall behavior of the RGB morphology as a function of cluster metallicity. The behavior of the RGB shape parameters was also compared with the previous observational calibration relation and theoretical predictions of the Yonsei-Yale isochrones. Our results of studies for stellar spatial distribution around globular clusters and the morphological properties of RGB stars in globular clusters could add further observational evidence of merging scenario of galaxy formation.

• Journal of The Korean Astronomical Society
• /
• v.27 no.2
• /
• pp.119-132
• /
• 1994

The BVR CCD photometry was performed for the globular cluster M13 down to $V=19^m$ over the region from the center to the west 13 arcmin and the CMD of M13 is investigated. The major photometric error in the crowded field which is due to the variation in the sky background was corrected by the median filtering method and the direct sky method. Some characteristics of the CMD of M13 obtained in the present study are as follows: Firstly, the distribution of stars on the CMD is well consistent with the mean lines of Sandage(1970) along the red giant branch(RGB), horizontal branch(HB) and asymtotic giant branch(AGB). Secondly, some gaps exists along the RGB and blue horizontal branch(BHB). Thirdly, the UV-bright stars are more concentrated at the inner region of the cluster.

• Journal of The Korean Astronomical Society
• /
• v.35 no.2
• /
• pp.75-85
• /
• 2002

We present N-body simulations of globular clusters including gravitational field of the Galaxy, in order to study effects of tidal field systematically on the shape of outer parts of globular clusters using NBODY6. The Galaxy is assumed to be composed of central bulge and outer halo. We mvestigate the cluster of multi-mass models with a power-law initial mass function (IMF) starting with different initial masses, initial number of particles, different slopes of the IMF and different orbits of the cluster. We have examined the general evolution of the clusters, the shape of outer parts of the clusters, density profiles and the direction of tidal tails. The density profiles appear to become somewhat shallower just outside the tidal boundary consistent with some observed data. The position angle of the tidal tall depends on the location in the Galaxy as well as the direction of the motion of. clusters. We found that the clusters become more elongated at the apogalacticon than at the pengalacticon. The tidal tails may be used to trace the orbital paths of globular clusters.

• The Bulletin of The Korean Astronomical Society
• /
• v.46 no.2
• /
• pp.41.3-42
• /
• 2021

Coma cluster (Abell 1656) is one of the most massive local galaxy clusters such as Virgo, Fornax, and Perseus, which holds a large collection of globular clusters. Globular cluster systems (GCSs) in a galaxy cluster tell us a history of hierarchical cluster assembly and intracluster GCs (ICGCs) are known to trace the gravitational potential of the galaxy cluster. Previous studies of GCSs in Coma mainly utilized data obtained using Hubble Space Telescope (HST) with high spatial resolution. However, most of the data were based on narrow-field pointing observations. In this study we present the widest survey of GCSs in the Coma cluster using the archival Subaru/Hyper Suprime-Cam (HSC) g and r images, supplemented with the archival HST images. The Coma GCSs are largely extended in E-W and SW direction, along the general direction of Coma-Abell 1367 filament. This global structure of the GCSs is consistent with the spatial distribution of the intracluster light (ICL). ICGC spatial distribution is largely extended to almost ~50% of the virial radius. Most of these ICGCs are blue and metal-poor, which supports the scenario that ICGCs are mainly originated from dwarf galaxies and some proportion from brighter galaxies. Implications of the results will be discussed.

• Journal of Astronomy and Space Sciences
• /
• v.34 no.2
• /
• pp.83-97
• /
• 2017

We present extra-tidal features of spatial configuration of stars around three metal-poor globular clusters (NGC 6266, NGC 6273, NGC 6681) located in the Galactic bulge. The wide-field photometric data were obtained in BVI bands with the MOSAIC II camera at CTIO 4 m Blanco telescope. The derived color-magnitude diagrams (CMDs) contain stars in a total $71^{\prime}{\times}71^{\prime}$ area including a cluster and its surrounding field outside of the tidal radius of the cluster. Applying statistical filtering technique, we minimized the field star contaminations on the obtained cluster CMDs and extracted the cluster members. On the spatial stellar density maps around the target clusters, we found overdensity features beyond the tidal radii of the clusters. We also found that the radial density profiles of the clusters show departures from the best-fit King model for their outer regions which support the overdensity patterns.