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- The Korean Astronomical Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-4614 (ISSN : 1225-4614)
1225-4614
- DB구축현황 : 1,211건 (DB Construction : 1,211 Articles)
총 게시글 1,211건
페이지 44/122
431
- Kim, Kyoo-Hyun
- Journal of the Korean astronomical society = 천문학회지
- 39, n.3
- pp.57-71
- 2006
- 원문 바로보기
We investigated the structural parameters of a sample of 30 dwarf galaxies(15 dEs and 15 dS0s) in the Virgo Cluster using i-band images from the Sloan Digital Sky Survey Data Release 4. Among 28 galaxies for which surface brightness profiles were derived from ellipse fittings, 23 galaxies had a single component that was adequately described by a generalized <TEX>$S\acute{e}rsic$</TEX> function with a shape parameter ranging from n=0.5 to 2, while 5 galaxies(2 dEs and 3 dS0s) had bulge and disk components that were fitted by a generalized <TEX>$S\acute{e}rsic$</TEX> function and an exponential function, respectively. Since the majority of dwarf galaxies in the present sample had a single component, it seems likely that genuine dS0 galaxies that have disk and bulge components are quite rare in the Virgo Cluster. The similarity in structural parameters of genuine dS0 galaxies in the Virgo Cluster with those of Magellanic-type galaxies implies that the progenitors of dwarf lenticular galaxies in the Virgo Cluster were most likely Magellanic-type galaxies if dS0s are harassed late-type spirals.
432
- Kim, Sang-Chul
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.115-123
- 2006
- 원문 바로보기
We present <TEX>$JHK_S$</TEX> 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 <TEX>$1.6{\pm}0.2$</TEX> Gyr, metallicity <TEX>$[Fe/H]=0.0{\pm}0.2$</TEX> dex, distance modulus<TEX>$(m-M)_0=10.4{\pm}0.3\;mag(d=1.2{\pm}02\;kpc)$</TEX>, and reddening <TEX>$E(B-V)=0.10{\pm}0.05$</TEX> mag. The parameters for the other old open cluster NGC 2394 are estimated to be <TEX>$age=1.1{\pm}0.2$</TEX> Gyr, <TEX>$[Fe/H]=0.0{\pm}0.2$</TEX> dex, <TEX>$(m-M)_0=9.1{\pm}0.4\;mag(d=660{\pm}120\;pc)$</TEX>, and <TEX>$E(B-V)=0.05{\pm}0.10$</TEX> 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 <TEX>${\Delta}[Fe/H]/{\Delta}R_{gc}=-0.067{\pm}0.009\;dex\;kpc^{-1}$</TEX>.
433
- Kyeong, Jae-Mann
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.89-94
- 2006
- 원문 바로보기
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 <TEX>$A_v=2-6$</TEX> from the comparison with the theoretical values given by the Leitherer et al.(1999)'s theoretical star cluster model.
434
- Lee Jae-Woo
- Journal of the Korean astronomical society = 천문학회지
- 39, n.2
- pp.41-50
- 2006
- 원문 바로보기
We present the results of new multi-color CCD photometry for the contact binary XZ Leo, together with reasonable explanations for the period and light variations. Six new times of minimum light have been determined. A period study with all available timings confirms Qian's (2001) finding that the O-C residuals have varied secularly according to <TEX>$dP/dt\;=\;+8.20{\times}10^{-8}\;d\;yr^{-l}$</TEX>. This trend could be interpreted as a conservative mass transfer from the less massive cool secondary to the more massive hot primary in the system with a mass flow rate of about <TEX>$5.37{\times}10^{-8}\;M_{\odot}\;yr^{-l}$</TEX>. By simultaneous analysis of our light curves and the previously published radial-velocity data, a consistent set of light and velocity parameters for XZ Leo is obtained. The small differences between the observed and theoretical light curves are modelled by a blue third light and by a hot spot near the neck of the primary component. Our period study does not support the tertiary light but the hot region which may be formed by gas streams from the cool secondary. The solution indicates that XZ Leo is a deep contact binary with the values of q=0.343, <TEX>$i=78^{\circ}.8$</TEX>, <TEX>${\Delta}(T_1-T_2)=126\;K$</TEX>, and f=33.6 %, differing much from those of Niarchos et al. (1994). Absolute parameters of XZ Leo are determined as follows: <TEX>$M_1=1.84\;M_{\odot},\;M_2=0.63\;M_{\odot},\;R_1=1.75\;R_{\odot},\;R_2=1.10\;R_{\odot},\;L_1=7.19\;L_{\odot},\;and\;L_2=2.66\;L_{\odot}$</TEX>.
435
- Lee Chung-Uk
- Journal of the Korean astronomical society = 천문학회지
- 39, n.1
- pp.25-30
- 2006
- 원문 바로보기
We completed four color light curves of the near-contact binary CN And during three nights from September to December 2004 using the 61-cm reflector and BV RI filters at Sobaeksan Observatory. We determined four new times of minimum light (two timings for primary eclipse, two for secondary). Newly obtained BV RI light curves and the radial velocity curves from Rucinski et a1. (2000) were simultaneously analyzed to derive the system parameters of CN And. We used the semi-detached mode 4 of the 2003-version of the Wilson-Devinney binary model, and interpreted the asymmetry of the light curve by introducing two spots; a cool spot on the primary component and a hot spot on the secondary component. New photometric parameters are not much different from those of Cicek et a1. (2005), and it is considered that the system is in the era of broken contact. From the orbital period study with all available timings including our data, we found a continous period decrease with a rate of <TEX>$P_{obs}=--1.82{\times}10^{-7}\;d\;yr^{-1}$</TEX> that can be explained with two possible mechanisms. We think the most likely cause of the period decrease is a thermal mass transfer from the primary to the secondary component, rather than angular momentum loss due to a magnetic stellar wind.
436
- Park Geum-Sook
- Journal of the Korean astronomical society = 천문학회지
- 39, n.2
- pp.31-40
- 2006
- 원문 바로보기
Near-IR <TEX>$H_2$</TEX> emission features in the northern region of the Orion A giant molecular cloud were observed in the <TEX>$CO\;J\;=\;1\;{\rightarrow}\;0$</TEX> line in search of CO outflows. Out of the 30 sources surveyed, CO line wings were detected toward 28 positions, suggesting a strong correlation between <TEX>$H_2$</TEX> jets and CO outflows. Blueshifted wings were detected toward 26 positions while redshifted wings were detected toward 15 positions, which suggests that there is a bias in the source selection. The bias is more severe in OMC 3 than in OMC 2. Since the protostars in OMC 3 are younger and more deeply embedded, the bias may be caused by the difference of extinction between blueshifted and redshifted outflows. Some physical parameters of the outflows were derived from the line profiles.
437
- Bondar, A.
- Journal of the Korean astronomical society = 천문학회지
- 39, n.3
- pp.73-80
- 2006
- 원문 바로보기
We analyze the extinction law towards several B1V stars-members of our Galaxy, searching for possible discrepancies from the galactic average extinction curve. Our photometric data allow to build extinction curves in a very broad range: from extreme UV till infrared. Two-colour diagrams, based on the collected photometric data from the ANS UV satellite, published UBV measurements and on the infrared 2MASS data of the selected stars, are constructed. Slopes of the fitted straight lines are used to build the average extinction curve and to search for discrepant objects. The selected stars have also been observed spectroscopically from the Terskol and ESO Observatories; these spectra allow to check their Sp/L's. The spectra of only about 30% of the initially selected objects resemble closely that of HD144470, considered as the standard of B1 V type. Other spectra either show some emission features or belong clearly to another spectral types. They are not used to build the extinction curve. Two-colour diagrams, constructed for the selected B1 V stars, showing no emission stellar features, prove that the interstellar extinction law is homogeneous in the Galaxy. Both the shape of the curve and the total-to-selective extinction ratio do not differ from the galactic average and the canonical value(3.1) respectively. The circumstellar emissions usually cause some discrepancies from the average interstellar extinction law; the discrepancies observed in the extraterrestrial ultraviolet, usually follow some misclassifications.
438
- Park Yong-Sun
- Journal of the Korean astronomical society = 천문학회지
- 39, n.2
- pp.51-56
- 2006
- 원문 바로보기
We report the development of a semi-VLBI observation system operating at 21 cm and present the measurement of visibility function toward the sun using this system. The system consists of two 2.3 meter antennas with a maximum separation of 35 meter, a conventional high speed data acquisition system, and a set of programs for software correlation. Since two local oscillators of receiver modules are independent, data had to be fringe-fitted to yield the visibility amplitude. It is found that the visibility amplitude decreases and then bounces back as baseline increases. We confirm that solar disk with brighter limb best explains the measured visibility amplitude.
439
- Morcos, A.B.
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.81-87
- 2006
- 원문 바로보기
A relation between temperature and time has been constructed in the self-consistent model(SCM). This relation is used to calculate the a CMBR temperature. This temperature has been found to be 2.9K. The temperature gradient of microwave background radiation(CMBR) is calculated in the Self Consistent Model. Two relations between Hubble parameter and time derivative of the temperature, have been presented in two different cases. In the first case the temperature is treated as a function of time only, while in the other one, it is assumed to be a function in time and solid angle, beside the assumption that the universe expands adiabatically.
440
- KIM SANG CHUL
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.85-88
- 2005
- 원문 바로보기
Construction of the Virtual Observatory (VO) is a great concern to the astronomical community in the 21st century. We present an outline of the concept and necessity of the va and the current status of various VO projects including the 15 national ones and the International Virtual Observatory Alliance (IVOA). We summarize the possible science cases that could be solved by using the VO data/tools, real science cases which are the results of using current VO tools, and our own work of using AstroGrid, the United Kingdom national VO, for a research on star formation history of galaxies.