• Journal of The Korean Astronomical Society
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• 제28권1호
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• pp.31-43
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• 1995

We present UBVRI CCD photometry of the Type Ie supernova SN 19941 in M51 which was discovered on April 2, 1994 (UT). UBVRI CCD photometry of SN 1994 I were obtained for the period of the first two months from April 4, 1994, using the Seoul National University Observatory 60 cm telescope. The light curves of SN 19941 show several interesting features: (a) SN 19941 reaches the maximum brightness at B-band on April 8.23 (B = 13.68 mag), at V-band on April 9.10 (V = 12.89 mag), and at I-band on April 10.32 (I = 12.48 mag); (b) The light curves around the maximum brightness are much narrower than those of other types of supernovae; (c) The light curves after the peak decline more steeply than those of other types of supernovae; and (d) The colors get redder from $(V-R){\approx}0.2 mag ((V - I){\approx} 0.3 mag, (B - V){\approx}0.7 mag)$ on April 4 to $(V-R){\approx}0.6 mag ((V-1){\approx}0.9 mag, (B-V){\approx}1.3 mag)$ on April 18. Afterwards (V - R) colors get bluer slightly $(by\~0.005 mag/day)$, while (V-I) colors stay almost constant around $(V-1){\approx}1.0 mag$. The color at the maximum brightness is (B-V)=0.9 mag, which is $\~1$mag redder than the mean color of typical Type la supernovae at the maximum brightness. The light curves of SN 1994I are similar to those of the Type Ie supernova SN 1962L in NGC 1073. Adopting the distance modulus of $(m-M)_0 = 29.2 mag$ and the reddening of E(B - V) = 0.45 mag [Iwamoto et al. 1994, preprint for ApJ], we derive absolute magnitudes at the maximum brightness of SN 1994I, Mv(max) = -17.7 mag and MB(max) = -17.4 mag. This result shows that SN 1994I was $\~2$mag fainter at the maximum brightness compared with typical Type Ia supernovae. A narrower peak and faster decline after the maximum in the light curve of SN 1994I compared with other types of supernovae indicate that the progenitor of SN 1994I might be a lower mass star compared with those of other types of supernovae.

• Journal of The Korean Astronomical Society
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• 제30권1호
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• pp.27-70
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• 1997

The brightest stars in galaxies have been used as distance indicators since Hubble. However, the accuracy of the brightest stars for distance estimates has been controversial. Recently, Rozanski & Rowan-Robinson [1994 : MNRAS, 271, 530] argued large errors of this method for the distance determination : 0.58 mag and 0.90 mag, respectively, for the brightest red stars and the brightest blue stars, while Karachentsev & Tikhonov [1994 : A&A, 286, 718] suggested much smaller errors in the distance determination than the former: 0.37 mag for the brightest red stars and 0.46 mag for the brightest blue stars. The reasons for these conflicting results are not yet known. In this study we have investigated the accuracy of this method using a sample of 17 galaxies for which Cepheid distances are known and reliable photometry of the brightest stars are available. We have obtained the calibrations of the relations between the mean luminosities of the three blue and red brightest supergiants (BSGs and RSGs, respectively) and the total luminosities of the parent galaxies: $= 0.21M_B^T- 3.84, \sigma(M_v) = 0.37 mag,\;and\;\delta_{\mu0}=0.47$ mag for the brightest red supergiants, and $= 0.30M_B^T -3.02, \sigma(M_B)\;=\;0.55 mag,\;and\; \delta_{\mu0}=0.79mag$ for the brightest blue supergiants. Also it is found that the errors in the distance determination are reduced by a factor of two, as the observing wavelengths increase from B-band to K-band. In conclusion, the brightest red supergiants are considered to be useful for determining the distances to resolved late-type galaxies.

• Journal of The Korean Astronomical Society
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• 제50권3호
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• pp.79-92
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• 2017

We present a BV I optical photometric study of the old open cluster Ruprecht 6 using the data obtained with the SMARTS 1.0 m telescope at the CTIO, Chile. Its color-magnitude diagrams show the clear existence of the main-sequence stars, whose turn-off point is located around $V{\approx}18.45mag$ and $B-V{\approx}0.85mag$. Three red clump (RC) stars are identified at V = 16.00 mag, I = 14.41 mag and B - V = 1.35 mag. From the mean $K_s-band$ magnitude of RC stars ($K_s=12.39{\pm}0.21mag$) in Ruprecht 6 from 2MASS photometry and the known absolute magnitudes of the RC stars ($M_{K_S}=-1.595{\pm}0.025mag$), we obtain the distance modulus to Ruprecht 6 of $(m-M)_0=13.84{\pm}0.21mag$ ($d=5.86{\pm}0.60kpc$). From the ($J-K_s$) and (B - V ) colors of the RC stars, comparison of the (B - V ) and (V - I) colors of the bright stars in Ruprecht 6 with those of the intrinsic colors of dwarf and giant stars, and the PARSEC isochrone fittings, we derive the reddening values of E(B - V ) = 0.42 mag and E(V - I) = 0.60 mag. Using the PARSEC isochrone fittings onto the color-magnitude diagrams, we estimate the age and metallicity to be: $log(t)=9.50{\pm}0.10(t=3.16{\pm}0.82Gyr)$ and $[Fe/H]=-0.42{\pm}0.04dex$. We present the Galactocentric radial metallicity gradient analysis for old (age > 1 Gyr) open clusters of the Dias et al. catalog, which likely follow a single relation of $[Fe/H]=(-0.034{\pm}0.007)R_{GC}+(0.190{\pm}0.080)$ (rms = 0.201) for the whole radial range or a dual relation of $[Fe/H]=(-0.077{\pm}0.017)R_{GC}+(0.609{\pm}0.161)$ (rms = 0.152) and constant ([Fe/H] ~ -0.3 dex) value, inside and outside of RGC ~ 12 kpc, respectively. The metallicity and Galactocentric radius ($13.28{\pm}0.54kpc$) of Ruprecht 6 obtained in this study seem to be consistent with both of the relations.

• Journal of the Korean earth science society
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• 제40권5호
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• pp.464-475
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• 2019

We measured night sky brightness (NSB) over the downtown using a Digital Single Lens Reflex (DSLR) camera combined to a small telescope for educational purpose, considering that most secondary schools are located in urban areas and have limitation in the equipment for astronomical observation. Raw format images from DSLR camera are not affected by various camera settings except for the ISO, and the typical photometric uncertainty including filter transformation is about 0.1 mag. Near the zenith, the NSB of the B, V, and r-band is 17.5, 17.1, and $16.9mag\;arcsec^{-2}$, respectively. The approximate limiting magnitude is derived to be 17.5 mag at B-band and 17 mag at V, r-band. A large scale artificial light close to the observation site is the dominant cause for making observing condition worse, increasing the NSB by $0.6mag\;arcseec^{-2}$ regardless of the altitude and filter.

• The Transactions of the Korean Institute of Electrical Engineers B
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• 제48권10호
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• pp.571-578
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• 1999

Current waveform control of pulse MAG welding power source is studied so that welding of thin plates may obtain high speed and improved performance. In this paper, waveform control method is proposed, digital controller using DSP is able to control the current waveform precisely. High speed welding of thin plates using pulse MAG welding method is made possible. Performance test for 1.2mm thin plates is carried out, output waveform and welding performance is analyzed.

• Journal of Astronomy and Space Sciences
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• 제21권3호
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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.

• Journal of The Korean Astronomical Society
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• 제38권3호
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• pp.345-355
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• 2005

We present a photometric study of the star cluster system in the merging galaxy NGC 1487, based on the BI photometry obtained from the F450W and F814W images in the HST /WFPC2 archive data. We have found about 560 star cluster candidates in NGC 1487, using the morphological parameters of the objects. We have investigated several photometric characteristics of the clusters: color-magnitude diagrams (CMDs), color distribution, spatial distribution, age, size and luminosity function. The CMD of the bright clusters with 18.5 < B < 24 mag in NGC 1487 shows three major populations of clusters: a blue cluster population with $(B-I){\le}0.45$, an intermediate-color cluster population with $0.45<(B-I){\le}1.55$, and a red cluster population with (B - I) > 1.55. The intermediate-color population is the most dominant among the three populations. The brightest clusters in the blue and intermediate- color populations are as bright as $B{\approx}18mag$ ($M_B{\approx}-12mag$), which are three magnitudes brighter than those in the red population. The blue and intermediate-color clusters are strongly concentrated on the bright condensations, while the red clusters are relatively more scattered over the galaxy. The CMD of these clusters is found to be remarkably similar to that of the clusters in the famous interacting system M51. From this we suggest that the intermediate-color clusters were, probably, formed during the merging process which occurred about 500 Myrs ago.

• Journal of The Korean Astronomical Society
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• 제39권4호
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• pp.115-123
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• 2006

We present $JHK_S$ near-infrared CCD photometric study for the Galactic open clusters NGC 1641 and NGC 2394. These clusters have never been studied before, and we provide, for the first time the cluster parameters; reddening, distance, metallicity and age. NGC 1641 is an old open cluster with age $1.6{\pm}0.2$ Gyr, metallicity $[Fe/H]=0.0{\pm}0.2$ dex, distance modulus$(m-M)_0=10.4{\pm}0.3\;mag(d=1.2{\pm}02\;kpc)$, and reddening $E(B-V)=0.10{\pm}0.05$ mag. The parameters for the other old open cluster NGC 2394 are estimated to be $age=1.1{\pm}0.2$ Gyr, $[Fe/H]=0.0{\pm}0.2$ dex, $(m-M)_0=9.1{\pm}0.4\;mag(d=660{\pm}120\;pc)$, and $E(B-V)=0.05{\pm}0.10$ mag. The metallicities and distance values for these two old open clusters are consistent with the relation between the metallicities and the Galactocentric distances of other old open clusters. We find the metallicity gradient of 53 old open clusters including NGC 1641 and NGC 2394 to be ${\Delta}[Fe/H]/{\Delta}R_{gc}=-0.067{\pm}0.009\;dex\;kpc^{-1}$.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제34권6B호
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• pp.615-622
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• 2009

In this paper, we consider the problem of applying NEMO in PMIPv6, and propose a method to support network mobility. When an MR enters a PMIPv6 domain, an MAG recognizes the MR to access using the BU message. And the MAG makes a tunnel between the MAG and the MR. The MR do not make tunnel fundamentally except for handover. Therefore, the PMIPv6 protocol needs to modify the original algorithm and the BCE data filed. However, the proposed method can use NEMO without protocol modification. To show verification, we implement our proposed algorithm with added BCE data filed using C program, and configure a testbed network. Through a network connectivity procedure, we can see that our proposed method can support network mobility within the PMIPv6 network.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제35권3B호
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• pp.373-379
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• 2010

In this paper, we propose a novel MAS algorithm to reduce the amount of signaling and data traffics. To notify an MIPv6 host of the proposed operation, we design a new binding registration function into the MAG, and suggest the modified RS and RA messages. The binding registration in the MAG instead of the LMA is accomplished to support the PMIPv6, whereas a 1-bit N flag in the RS and RA message indicates where the MAG supports the PMIPv6 or not. Our proposed algorithm has the advantage for MIPv6 hosts in the PMIPv6 network in the viewpoints of network utilization and performance. To show the verification and better performance of the MAS algorithm, we evaluate the amount of traffic and its related performance, and compares those with performance of the normal PMIPv6. These results show that our proposed algorithm can operate efficiently and give better performance for MIPv6 hosts in the PMIPv6 network.