• 천문학회보
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• 제38권2호
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• pp.74.1-74.1
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• 2013

We have performed new narrow-band calcium photometry for Milky Way globular clusters (GCs) and detected multiple red giant branches (RGBs) in some massive GCs. Our new calcium filter was designed to avoid the CN contamination below $3883{\AA}$ and to measure only Ca II H&K lines. The fact that we are detecting multiple RGBs from the new filter is suggesting that they are indeed different in calcium abundance, which can only be produced by supernovae (SNe). Therefore, the presence of the multiple RGBs for the peculiar GCs in the calcium photometry is best understood if the later generation of stars are enhanced in some SNe products. In this talk, we will present our progress in the calcium photometry for the peculiar GCs showing the multiple RGBs.

• 천문학회보
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• 제37권2호
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• pp.77.2-77.2
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• 2012

We have studied the physical properties of X-ray point sources in galaxy clusters for years based on the archival observations using the most sophisticated space X-ray observatory, Chandra X-ray Observatory. Because the ultimate goal of the study is comparing the physical properties of X-ray point sources found in galaxy clusters to those in X-ray blank fields; blank fields are the regions in the sky where any noticeable cosmic diffuse X-ray emission is not observed, an important key issue regarding this study is picking out the point sources related with galaxy clusters. However we do not have red-shift information of all the X-ray point sources. Therefore as a first order approximation we will consider the point sources with smaller projected cluster-centric distance than the adopted size of galaxy clusters. As a first step of this study we perform X-ray surface photometry of ~600 galaxy clusters based on ~800 Chandra ACIS observations. We carefully investigate the radial structures of diffuse X-ray emission in 3 different energy bands. Based on the highly accurate surface photometry we determine the characteristic size of diffuse X-ray emission (i.e., the boundary of X-ray emission). We also investigate the cosmological evolution of this characteristic size of galaxy clusters. General discussion regarding the two dimensional morphology of galaxy clusters will be presented.

• 천문학회지
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• 제38권2호
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• pp.145-148
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• 2005

We present a photometric study of galaxies in the central regions of six nearby galaxy clusters at redshift z=0.0231${\~}$0.0951. We have derived BVI photometry of the galaxies from the CCD images obtained at the Bohyunsan Optical Astronomical Observatory (BOAO) in Korea, and JHKs photometry of the bright galaxies from the 2MASS extended source catalog. Comparing the galaxy photometry results with the simple stellar population model of Bruzual & Charlot (2003) in the optical & NIR color-color diagrams, we have estimated the ages and metallicities of early type galaxies. We have found that the observed galaxies had recent star-formation mostly 5 ${\~}$ 7 Gyrs ago but the spread in age estimation is rather large. The average metallicities are [Fe/H]=0.l${\~}$0.5 dex. These results support the hypothesis that large early type galaxies in clusters are formed via hierarchical merging of smaller galaxies.

• 천문학회지
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• 제41권5호
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• pp.109-119
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• 2008

We present an optical-infrared photometric study of galaxies in six nearby clusters of galaxies at $z=0.041{\sim}0.098$ (A1436, A1773, A1809, A2048, A2142, and A2152). Using BV I photometry obtained at the Bohyunsan Optical Astronomical observatory and $JHK_S$ photometry extracted from the 2-Micron All-Sky Survey catalog, we investigate the colors of galaxies in the clusters. Using the (B - V) versus ($I\;-\;K_S$) color-color diagrams in comparison with the simple stellar population model, we estimate the ages and metallicities of bright early-type member galaxies. Early-type galaxies in each cluster show the color-magnitude relation. Ages and metallicities of early-type members show little dependence on their velocity dispersions. Mean ages of early-types in the clusters range from 3 Gyr to 20 Gyr, showing a large dispersion, and mean metallicities range from Z = 0.03 to 0.05 above the solar value, showing a negligible dispersion.

• 천문학회지
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• 제31권2호
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• pp.141-160
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• 1998

We have conducted BV RI CCD surface photometry of three spiral galaxies ESO 598-G009, NGC 1515 and NGC 7456. In order to understand the morphological properties and luminosity distribution characteristics for each galaxy, we derived isophotal map, position angle profile, ellipticity profile, luminosity profile, color profile and color contour map. ESO 598-G009, which has a bright bulge component and a ring, shows a trace of gravitational interaction. NGC 1515 is a spiral galaxy with a bar and dust lane. NGC 7456 shows typical characteristics of a late type spiral galaxy.

• 천문학회보
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• 제38권2호
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• pp.63.2-63.2
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• 2013

Unlike the conventional wisdom, observations made during the past decade have revealed that many globular clusters possess more than one stellar population. Here, we have discovered evidence for multiple red giant branches (RGBs) in the globular cluster NGC 6388 from the narrow-band Calcium and Str$\ddot{o}$mgren b & y (Caby) photometry. In order to confirm the difference in Calcium abundance, we have acquired the low resolution spectroscopy for these RGB stars. In this paper, we will present results of our photometry and hand in the preliminary results of spectroscopic observations.

• 천문학회보
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• 제36권2호
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• pp.144.2-144.2
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• 2011

A dwarf irregular galaxy IC10 in the Local Group is the nearest starburst galaxy, playing an important role revealing the details of starburst. It is located close to the Galactic plane so that it suffers from severe foreground reddening. Therefore much less is known about the property of this galaxy compared with other galaxies in the Local Group. So are star clusters in this galaxy. We present a photometric study of the star clusters in IC10. 57 star clusters are already found from HST images in previous studies, and we newly found 15 star clusters using Local Group Survey data and SUBARU/Suprime-Cam data. We derive UBVRI integrated photometry of these star clusters from the images from Local Group Survey data and JHKs photometry taken with SUBARU/MOIRCS. Then we derive age and mass of these clusters using the spectral energy distribution fitting with the simple stellar population models. We discuss the photometric and physical properties of these star clusters and its implication.

• 천문학회지
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• 제32권2호
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• pp.83-89
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• 1999

We have conducted a V, I, J, and H surface photometry of a barred galaxy NGC 4314 to analyze the morphology and luminosity distribution of the galaxy. By applying a semi two-dimensional profile decomposition method, we derived the luminosity fractions and the scale lengths of the three distinct components, bulge, disk, and bar: $L_b {\approx}0.35,\;L_d{\approx}0.35,\;L_{bar}{\approx}0.30,\;r_e{\approx}22",\;r_o {\approx} 50"$, and a $\approx$ 60". The bulge of NGC 4314 seems to be triaxial due to the isophotal twists but its luminosity distribution is well approximated by the $r^{1/4}$-law.

• 천문학회지
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• 제39권4호
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• pp.89-94
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• 2006

We present JHK-band near-infrared photometry of the star clusters in the dwarf irregular galaxy IC 5152. After excluding possible foreground stars, a number of candidate star clusters are identified in the near-infrared images of IC 5152, which include young populations. Especially, five young star clusters are identified in the(J-H, H-K) two color diagram and the total extinction values toward these clusters are estimated to be $A_v=2-6$ from the comparison with the theoretical values given by the Leitherer et al.(1999)'s theoretical star cluster model.

• 천문학회지
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• 제29권spc1호
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• pp.77-78
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• 1996

We perfom a large project for complex study of Blue Compact Galaxies (BCGs) with strong star formation, which includes optical spectroscopy, BVR CCD photometry and HI 21 cm radio survey. The most interesting galaxies are studied also with HST and VLA. In the frame of this project we began the study of H$\alpha$ morphology of BCGs with 6-m telescope. We present and discuss here the results for the first 6 galaxies. We found the noticeable variety of forms for H$\alpha$ morphology comparing to broad band images: from very compact HII region in very center of stellar body (Mark 996, possible dwarf post-merger, old galaxy experiencing strong star formation burst), to very extended gas emission encompassing the whole area traced by stars (SBS 0335-052, the most probable young galaxy in formation).