• Publications of The Korean Astronomical Society
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• v.11 no.1
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• pp.139-146
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• 1996

Galactic open clusters NGC 1907 and NGC 1912 are known as a binary cluster candidate by Subramaniam et al.(1995). With the SNUO 0.6m telescope, UBV CCD photometric observations were performed for 62 stars in NGC 1907 within the area of $8'{\times}8'$ and 203 stars in NGC 1912 within the area of $15'{\times}15'$ area. We obtained C-M and C-C diagrams. Their mean reddenings are E(B-V) = $0.50{\pm}0.03$ for NGC 1907 and $0.27{\pm}0.03$ for NGC 1912. The distance moduli are estimated as $10.9{\pm}0.15$ and $10.4{\pm}0.10$ for NGC 1907 and NGC 1912, respectively. The ages for these clusters are $400{\pm}50Myr$ for NGC 1907 and $150{\pm}30Myr$ for NGC 1912. The distance difference of the two clusters is 300pc and the age difference is 150Myr. These results imply that the two clusters are not physically connected.

• 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.

• 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.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.393-395
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• 2015

Weak gravitational lensing is an efficient technique for detecting galaxy clusters and probing their mass distribution. We present a weak gravitational lensing analysis of a large sample of galaxy clusters. We have built a nearly complete sample of 50 optically rich clusters, located in the redshift range 0.1 < z < 0.6 and observed in the Canada France Hawaii Telescope Legacy Survey (CFHT-LS). We used weak gravitational lensing to measure, for each galaxy cluster, the density radial profile, the total mass and the mass-to-light ratio (by comparing with the total luminosity of the member galaxies). This project is a preliminary step towards the next analysis of the weak lensing galaxy clusters in the surveys KiDS and VOICE, which are currently collecting data with the VLT Survey Telescope, in Chile.

• The Bulletin of The Korean Astronomical Society
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• v.26 no.1
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• pp.50.2-50.2
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• 2001

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.29.2-29.2
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• 2009

During the last four years, we have performed Sejong/ARCSEC Ca uvby survey using the CTIO-1m telescope aimed at obtaining Ca uvby photometry for about 50 globular clusters and selected fields in Baade's Windows. Our results show that Ca uvby photometric system can provide a powerful method to probe multiple populations in Galactic globular clusters. We will discuss the multiple stellar population in the globular cluster NGC6218 and NGC6752 as illustrations.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.49.4-50
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• 2020

We introduce a novel method for reconstructing the projected matter distributions of galaxy clusters with weak-lensing (WL) data based on convolutional neural network (CNN). We control the noise level of the galaxy shear catalog such that it mimics the typical properties of the existing Subaru/Suprime-Cam WL observations of galaxy clusters. We find that our mass reconstruction based on multi-layered CNN with architectures of alternating convolution and trans-convolution filters significantly outperforms the traditional mass reconstruction methods.

• 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.

• Publications of The Korean Astronomical Society
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• v.23 no.2
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• pp.17-23
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• 2008

From the short-period variability survey (SPVS), we obtained time-series BV CCD images in the region of an open cluster M50 (NGC 2323) for 10 nights from 2008 February 9 to 27. The observation was performed using a small refracting telescope (${\phi}$=155mm, f=1050mm) in Bohyunsan Optical Astronomy Observatory (BOAO). M50 is included in the observing field of ASAS (The All Sky Automated Survey). In the region of M50, we found 8 new variable stars including two ${\delta}$ Scuti stars with short-periods and very small amplitudes. There are known nine variable stars by the catalogues of ASAS and GCVS in the region. We confirmed the variability of the known variable stars for six and non-variability for three.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.43.2-43.2
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• 2021

Ram-pressure stripping (RPS) is known as the main driver of quenching the star formation (SF) activity in cluster galaxies. However, galaxies undergoing RPS in galaxy clusters often show blue star-forming knots in their disturbed disks and tails. The existence of these "jellyfish galaxies" implies that RPS can temporarily boost the SF activity of cluster galaxies. Thus, jellyfish galaxies are very unique and interesting targets to study the influence of RPS on their SF activity, in particular with integral field spectroscopy (IFS). While there have been many IFS studies of jellyfish galaxies in low-mass clusters (e.g., the GASP survey), IFS studies of those in massive clusters have been lacking. We present an IFS study of five jellyfish galaxies in massive clusters at intermediate redshifts using the Gemini GMOS/IFU. Their star formation rates (SFRs) are estimated to be up to 15 Mo/yr in the tails and 50 Mo/yr in the disks. These SFRs are by a factor of 10 higher than those of star-forming galaxies on the main sequence in the M*-SFR relation at similar redshifts. Our results suggest that the SF activity of jellyfish galaxies tends to be more enhanced in massive clusters than in low-mass clusters. This implies that strong RPS in massive clusters can trigger strong starbursts.