• Title/Summary/Keyword: globular cluster

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Spectroscopy of Globular Clusters in the Core of the Virgo Cluster

  • Ko, Youkyung;Hwang, Ho Seong;Lee, Myung Gyoon;Sohn, Jubee;Lim, Sungsoon;Park, Hong Soo
    • The Bulletin of The Korean Astronomical Society
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    • v.39 no.2
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    • pp.51.1-51.1
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    • 2014
  • The Virgo cluster, the nearest galaxy cluster, is dynamically young, hosting numerous globular clusters in galaxies as well as intracluster globular clusters (IGCs). We obtained spectra of globular cluster candidates in the core region of the Virgo cluster using Hectospec at MMT to study the kinematics of the globular clusters. The targets are located at a large range (50 kpc < d < 500 kpc) from M87, the most massive galaxy in Virgo. We distinguish the genuine globular cluster population in the targets by inspecting their spectral features and radial velocities. As a result, a significant number of IGCs are found. We present preliminary results of the kinematics of globular clusters in the Virgo core region.

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Globular Cluster Systems of Early-type Galaxies in Low-density Environments

  • Cho, Jae-Il;Sharples, Ray
    • Bulletin of the Korean Space Science Society
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    • 2010.04a
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    • pp.34.4-34.4
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    • 2010
  • We present the properties of globular cluster systems for 10 early-type galaxies in low density environments obtained using deep images from the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). Using the ACS Virgo Cluster Survey as a counterpart in high-density environments, we investigate the role of environment in determining the properties of their globular cluster systems. We detect a strong colour bimodality of globular cluster systems in half of our galaxy sample. It is found that there is a strong correlation between the colour and richness of globular cluster populations and their host galaxy luminosities: the less bright galaxies possess bluer and fewer globular clusters as also seen in rich cluster environments. However, the mean colour of globular clusters in our field sample are slightly bluer than those in cluster environments at a given galaxy luminosity, and the colour of the red population has a steeper slope with absolute luminosity. By employing the YEPS simple stellar population model, the colour offset corresponds to metallicity difference of $\Delta$[F e/H ] ~ 0.15 - 1.20 or an age difference of $\Delta$age ~ 2 Gyr on average, implying that GCs in field galaxies appear to be either less metal-rich or younger than those in cluster galaxies. Although we have found that galaxy environment has a subtle effect on the formation and metal enrichment of GC systems, host galaxy mass is the primary factor that determines the stellar populations of GCs and the galaxy itself.

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How did the peculiar S0 galaxy M85 form?

  • Ko, Youkyung;Lee, Myung Gyoon;Sohn, Jubee;Ryu, Jinhyuk;Jang, In Sung;Lim, Sungsoon;Park, Hong Soo;Hwang, Narae;Park, Byeong-Gon
    • The Bulletin of The Korean Astronomical Society
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    • v.40 no.1
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    • pp.46.1-46.1
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    • 2015
  • M85 is a merger remnant galaxy in the Virgo Cluster, showing complex merging features. Globular clusters in M85 are a good tracer of its merging history. To investigate globular cluster system of M85, we obtain deep and wide field images of M85 in ugi filters covering one square degree using CFHT/MegaCam. We discover about 1,000 globular cluster candidates in these images. The color distribution of the globular cluster candidates within r < 5' from M85 does not show a clear bimodality and blue globular cluster candidates are more than red ones. These features are different from those in massive early-type galaxies. The spatial distribution of the globular cluster candidates is elongated along the faint stellar light of M85. We also investigate the spatial distribution of sub-populations of the globular cluster candidates with different color and brightness and estimate their ages based on their color. We discuss these results in relation with the formation history of M85.

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SPECTROSCOPIC STUDY ON RED GIANTS IN GLOBULAR CLUSTERS (구상성단 거성들의 분광 연구)

  • LEE SANG-GAK
    • Publications of The Korean Astronomical Society
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    • v.15 no.spc1
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    • pp.15-30
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    • 2000
  • A large scatter of the chemical abundances among globular cluster red giants has been observed. Especially the chemical elements C, N, O, Na, Mg, and Al vary form star to star within globular clusters. Except for $\omega$ Cen and M22, most globular clusters could be considered to be monometallic of their iron peak elements within error ranges. The variations in light elements among globuar cluster giants appear much more pronounced than in field halo giants of comparable Fe-peak metallicity. It has been found that in general the nitrogen abundance is anticorrelated with both carbon and oxygen, while it is correlated with Na and AI. These intracluster abundance inhomogeneities can be interpreted either by mixing of nucleosythesized material from the deep stellar interior during the red giant branch phase of evolution or by inhomogeneities of primordially processed material, from which the stars were formed. The simple way of distingushing between two senarios is to obtain the element abundances of main-sequence stars in globular clusters, which are too faint for high resolution spectroscopic studies until now. Both 'evolutionary' and 'primodial' origins are accepted for explanations of abundance variations among red giants and CN-CH anticorrelations among main-sequence stars in globular clusters. This paper reviews chemical abundances of light elements among globular cluster giants, with brief reviews of cannonical stellar evolution of low mass stars after main-sequence and deep mixing for abundance variations of cluster giants, and a possible connection between deep mixing and second parameter.

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JK INFRARED PHOTOMETRY OF THE GLOBULAR CLUSTER M3

  • LEE SANG-GAK;LEE MYUNG GYOON;KIM EUNHYEUK
    • Journal of The Korean Astronomical Society
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    • v.29 no.2
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    • pp.171-179
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    • 1996
  • We have obtained the J K images of the central region of the globular cluster M3 (NGC5272), using the $256\pm256$ InSb array. We present JK photometry of bright red giant branch stars in the central $2'.2\pm2'.2$ region of M3. The infrared color-magnitude diagrams are presented. The comparison of the red giant branch of M3 with that of M13 confirms that both globular clusters have similar metal abundances.

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CCD PHOTOMETRY OF THE GLOBULAR CLUSTER NGC 4372

  • Yim, Hong-Suh;Lee, Young-Wook;Chum, Mun-Suk
    • 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.

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A Survey of Globular Cluster Systems of Massive Compact Elliptical Galaxies in the Local Universe

  • Kang, Jisu;Lee, Myung Gyoon
    • The Bulletin of The Korean Astronomical Society
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    • v.45 no.1
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    • pp.32.2-32.2
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    • 2020
  • Massive Compact Elliptical Galaxies (MCEGs) found in the local universe are as massive as normal galaxies but extremely compact (M∗ > 1011 Msun, Reff < 1.5 kpc). They are considered to be the relics of red nugget galaxies found at high redshift. They are not likely to have undergone many mergers, keeping their original mass and size. Moreover, it is expected that they host a dominant population of red (metal-rich) globular clusters rather than blue (metal-poor) ones. Indeed, Beasley et al. (2018) found that the color distribution of the cluster system of NGC 1277 is unimodal, showing only a red population. However, NGC 1277 is the only case whose cluster system was studied among MCEGs. In this study, we investigate globular cluster systems of 14 nearby MCEGs with a homogeneous data set of HST/WFC3 F814W/F160W archive images. We detect tens to hundreds of globular clusters in each galaxy and examine their color distributions. Surprisingly, the fractions of red globular clusters are similar to those of normal galaxies, and are much lower than that of NGC 1277. We additionally obtain Gemini/GMOS-N g'r'i' images of PGC 70520, one of the 14 nearby MCEGs, to detect more globular clusters from deeper and wider images. We will discuss the results from the Gemini data combined with the results from the HST data in relation with the formation of MCEGs.

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Discovery of a New Globular Cluster Candidate Hidden behind the Milky Way

  • Ryu, Jinhyuk;Lee, Myung Gyoon
    • The Bulletin of The Korean Astronomical Society
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    • v.39 no.2
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    • pp.84.2-84.2
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    • 2014
  • We report the discovery of a new Milky Way globular cluster (GC) candidate in the Galactic plane. We found this object during our WISE survey of star clusters in the Milky Way. We derived physical parameters of this object using the 2MASS JHK photometry. The color-magnitude diagram of the resolved stars shows a well-developed red giant branch (RGB). We derived its reddening, distance and metallicity. These results indicate that it is probably an old globular cluster, located behind the Galactic disk.

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Extra-tidal stars around globular clusters NGC 5024 and NGC 5053 and their chemical abundances

  • Chun, Sang-Hyun;Lee, Jae-Joon
    • The Bulletin of The Korean Astronomical Society
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    • v.43 no.2
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    • pp.40.2-40.2
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    • 2018
  • NGC 5024 and NGC 5053 are among the most metal-poor globular clusters in the Milky Way. Both globular clusters are considered to be accreted from dwarf galaxies (like Sagittarius dwarf galaxy or Magellanic clouds), and common stellar envelope and tidal tails between globular clusters are also detected. We present a search for extra-tidal cluster member candidates around these globular clusters from APOGEE survey data. Using 20 chemical elements (e.g., Fe, C, Mg, Al) and radial velocities, t-distributed stochastic neighbour embedding (t-SNE), which identifies an optimal mapping of a high-dimensional space into fewer dimensions, was explored, and we find that globular cluster stars are well separated from the field stars in 2-dimensional map from t-SNE. We also find that some stars selected in t-SNE map are placed outside of the tidal radius of the clusters. The proper motion of stars outside tidal radius is also comparable to that of globular clusters, which suggest that these stars are tidally decoupled from the globular clusters. We manually measure chemical abundances for the clusters and extra-tidal stars, and discuss the association of extra-tidal stars with the clusters.

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THE CCD PHOTOMETRY OF THE GLOBULAR CLUSTER NGC 362

  • LEE KANG HWAN;LEE SEE-WOO;SUNG HWANKYUNG
    • Journal of The Korean Astronomical Society
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    • v.31 no.1
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    • pp.19-26
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    • 1998
  • The wide field $(\~20'\times20')$ CCD photometry has been performed for more than 4,000 stars over a whole region of NGC 362 which is located inside the SMC halo. The Color-Magnitude diagram (CMD) and luminosit function (LF) for red giant branch (RGB) stars are presented, discussing a distinct bump along the RGB and some blue stars appearing in the blue horizontal branch (BHB) and above BHB. The anomalous globular cluster NGC 362 with highly populated red horizontal branch (RHB) stars is compared with the another anomalous globular cluster NGC 288 with highly populated BHB stars. A metal-rich, young blue component and metal-'poor, old red component of the SMC halo stars are examined.

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