• Journal of The Korean Astronomical Society
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• v.32 no.2
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• pp.109-117
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• 1999

UBVI CCD photometry has been obtained for a region around the Wolf-Rayet star WR 12. We found two young stellar associations in the observed field: the nearer one comprises the field members of Vela OBI association at d = 1.8kpc, while the farther one is the young open cluster Bochum 7 (Bo 7) at d = 4.8kpc. The stars associated with Bo 7 showed no central concentration which suggests that Bo 7 is not a young open cluster but simply a local concentration in the density of young stars belonging to the OB association (Vel OB3). These two associations have similar ages but remarkably different mass function slopes ($\Gamma$ = -2.1 $\pm$ 0.3 for Vel OBI and -1.0 $\pm$ 0.3 for Bo 7). The stars in Vel OBI shows an evident age spread (${\Delta}T\~ 9Myr$). We also found two strong H$\alpha$ emission stars - WR 12 and $\sharp$1066 - from narrow band H$\alpha$ photometry.

• Journal of Astronomy and Space Sciences
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• v.22 no.3
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• pp.211-222
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• 2005

Results of 6 nights of CCD VR photometry of the nova-like variable V603 Aquilae (Nova Aquilae 1918) obtained at the Mallorcian 35-cm telescope in July 2004 are reported. The ephemeris for the superhump maximum is Max.HJD=2453213.60546(96)+0.14813(10)E. The waves with $3.^d9,\;1.^d4,\;0.^d135$ are statistically significant, which may be interpreted as the negative superhump-orbital, the beat periods (negative superhump- positive superhump) and the negative superhump with low amplitude, respectively. Another possible time-scale is $0.^d8,$ which has no coincidence with the beat periods. Quasi-periodic oscillations with an effective period of 18 minutes have been detected, which are close to 15.6 minutes reported by some authors. Their effective semi-amplitudes are $^m.045\;and\;0^m.051$ for V and R, respectively. This corresponds to the 0.12 mag excess in the color index V-R as compared with the mean color, which can be understood as the pulsed emission in the hotter inner parts of the accretion disk, similar to that observed in TT Ari and MV Lyr.

• Journal of The Korean Astronomical Society
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• v.43 no.5
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• pp.141-152
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• 2010

UBV I CCD photometry is obtained for the open clusters NGC 4609 and Hogg 15 in Crux. For NGC 4609, CCD data are presented for the first time. From new photometry we derive the reddening, distance modulus and age of each cluster - NGC 4609 : E(B-V ) = $0.37{\pm}0.03$, $V_0-M_V=10.60{\pm}0.08$, log $\tau$= 7.7 $\pm$ 0.1; Hogg 15 : E(B - V ) = 1.13 $\pm$ 0.11, $V_0-M_V$ = 12.50 $\pm$ 0.15, log $\tau$ $\lesssim$ 6.6. The young age of Hogg 15 strongly implies that WR 47 is a member of the cluster. We also determine the mass function of these clusters and obtain a slope $\Gamma$ = -1.2 ($\pm$0.3) for NGC 4609 which is normal and a somewhat shallow slope (${\Gamma}=-0.95{\pm}0.5$) for Hogg 15.

• Journal of The Korean Astronomical Society
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• v.41 no.5
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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.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.40.4-41
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• 2018

We introduce a coordinate catalog for photometry of the KMTNet Galactic bulge observation program and how to find the microlensing event candidates in the photometry result. Basically, the KMTNet bulge program is monitoring a total of 27 target fields (108 deg2) with four different cadences of 0.5, 1.0, 2.5, and 5.0 hours. In order to measure the stellar flux of each target, we made a 'observation coordinate catalog' by using the 'OGLE-III catalog' and 'DoPhot package'. The catalog contains approximately 0.3 billion stars in the bulge fields. We also search for a microlensing event candidates by means of the 'Event Finder algorithm' which calculates the restricted single-lens fitting (t0, teff, u0; u0 = 0 or 1) model. As a result, we found more than 2,000 microlensing event candidates per each year including about 700 events from the other survey groups such as OGLE and MOA. In this year, we will improve our current pipeline system, e.g. upgrading the catalog and applying real-time photometry.

• Journal of The Korean Astronomical Society
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• v.26 no.1
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• pp.33-45
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• 1993

We have conducted surface photometry of a spiral galaxy NGC4419, by making use of photographic plates in U, B, V and R-bands taken by 105cm Schmidt Camera at Kiso Observatory. Two dimensional surface brightness distributions as well as luminosity profiles along the major axis are examined in detail to decipher the morphological properties of the galaxy. Analysis of the color distributions of NGC4419 shows that B-V and U-B colors remain constant throughout the galaxy with a weak trend of blue bulge in B-V color. The blue bulge might indicate an active star formation in the nucleus of NGC4419. For a quantitative analysis of the luminosity distribution of NGC4419, the observed luminosity profiles are decomposed into bulge and disk components, assuming the bulge component to follow de Vaucouleurs $\gamma^{1/4}-law$ while the disk component is assumed to be exponential. The fitting generally fails at the central part and at the shoulder near r = 15' where bulge and disk components overlap. The failure at the central part cannot be attributed wholly by the seeing disk since the core-radius of the central plateau is much larger than the width of point spread function. The failure at shoulder could be due to the luminosities from the spiral arms.

• Journal of The Korean Astronomical Society
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• v.32 no.1
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• pp.7-16
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• 1999

Open clusters are useful tools to investigate the structure and evolution of the Galactic disk. We have started a long-term project to obtain UBVI CCD photometry of open clusters which were little studied before, using the Doyak 1.8 m telescope of Bohyunsan Optical Astronomy Observatory in Korea. The primary goals of this project are (1) to make a catalog of UBVI photometry of open clusters, (2) to make an atlas of open clusters, and (3) to survey and monitor variable stars in open clusters. Here we describe this project and report the first results based on preliminary analysis of the data on four open clusters in the survey sample: Be 14, Cr 74, Biu 9, and NGC 2355. Isochrone fitting of the color-magnitude diagrams of the clusters shows that all of them are intermediate age to old (0.3-1.6 Gyrs) open clusters with moderate metallicity.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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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.

• Journal of Astronomy and Space Sciences
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• v.21 no.1
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• pp.1-10
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• 2004

We present BV CCD photometry of metal-rich globular cluster M71. Based on our color-magnitude diagram (CMD), we derive the distance to M71 using a sample of Hipparcos subdwarfs of similar metallicity. Our distance modulus is (m - M)v = 13.46(${\pm}0.17$. CMD comparison was also made between M71 and 47 Tuc. We confirm that there exists a significant age differonce(> 2 billion years) in spite of their Similarity in metallicity.

• Journal of Astronomy and Space Sciences
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• v.38 no.1
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• pp.45-53
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• 2021

GLONASS, a satellite navigation system developed in Russia since 1976, is defunct and orbits in an unstable attitude. The satellites in these problems are not managed and there is no precise information, which can increase the risk of collisions with other space objects. In this study, detailed attitude dynamic have to be analyzed through photometry data, which requires spin period and spin axis. The light curve data is obtained by observing through the photometer at the Graz station and the power spectrum is calculated to obtain the cycle of the satellite. The geometric relationship between observer and sun is analyzed for GLONASS-50 satellite. The box-wing model is applied to obtain the phase reflection of the satellite and obtain the Irradiation of the satellite through this information. In Light Curve and Irradiation, the spin axis is calculated for each peak points with the distance square minimum technique. The spin axis of the GLONASS-50 satellite is RA = 116°, Dec = 92°.