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- The Korean Astronomical Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-4614 (ISSN : 1225-4614)
1225-4614
- DB구축현황 : 1,187건 (DB Construction : 1,187 Articles)
총 게시글 1,187건
페이지 106/119
1051
- Kim, Kap-Sung
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.1
- pp.31-42
- 1990
- 원문 바로보기
Fine structures of a quiescent prominence are studied by analyzing high resolution H alpha filtergrams and H alpha line spectra observed at the Hida Observatory of Kyoto University. We have found two kinds of downward motions in the prominence. One of them is a movement with a constant acceleration below the solar gravity(<TEX>${\simeq}1/4g_s$</TEX>) and the other with an uniform velocity(<TEX>${\simeq}16Km/s$</TEX>). The average life time and the size of prominence knots are estimated to be about 7 minutes and 4000Km, respectively. Spatial and brightness distribution of knots are also presented in this paper. With the analytical solutions derived from magnetostatic equilibrium in the prominence, we have examined the filamentary structure based on the Kippenhahn-Schluter model. Sag angles of the magnetic fields supporting the prominence matter are predicted from the observed density profile.
1052
- Kim, Kyung-Ok
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.1
- pp.43-62
- 1990
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We present (U-B) and (U-V) radial color distributions of 103 galaxies based on the UBV multiaperture photometry compiled by Longo, de Vaucouleurs, and Corwin (1983). About half of the galaxies show radial negative color gradients (i. e., bluer at the outer parts of the galaxies). E and SO galaxies have similar color gradients. and there appears to be no correlation between the size of color gradients in these galaxies and their luminosity, but the luminous spiral galaxies tend to have steeper color gradients. The metallicity gradients of elliptical galaxies derived from the (U-V) color gradients agree with those from the magnesium gradients within the errors.
1053
- Ann, Hong-Bae
- 天文學會誌 = The journal of the Korean Astronomical Society
- 22, n.2
- pp.113-126
- 1989
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The initial mass functions (IMF) of 15 selected open clusters are investigated by making use of C-M diagrams and theoretical evolutionary tracks. Among 15 clusters 13 have peaks in their IMFs and it is thought to be not due to incomplete photometry but to intrinsic property. The mass where IMF peaks is about <TEX>$2\;M_{\odot}$</TEX> and it is similar to that of the second peak in the IMF of nearby field stars. The mean slope of the IMF in the high mass part is <TEX>$1.9{\pm}0.6$</TEX> with some variations among clusters. But there seems to be no correlation between the slope and physical parameters such as ages, diameters, and metal abundances.
1054
- Kim, Kang-Min
- 天文學會誌 = The journal of the Korean Astronomical Society
- 22, n.2
- pp.81-99
- 1989
- 원문 바로보기
Applying five morphological parameters defined along the main sequence (MS), red giant branch (RGB) and horizontal branch (HB) in the C-M diagram (CMD), and the transition period-luminosity relation for RR Lyrae variables, some basic physical quantities such as helium abundance, age, mass and luminosity are determined for 21 well observed globular clusters with combination of evolutionary models and atmospheric models properly chosen by the numerical test. The dependences of these quantities on the age and chemical abundance are investigated.
1055
- Hong, S.S.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 22, n.2
- pp.127-140
- 1989
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Problem of the diffuse radiation (DFR) transfer is solved exactly for pure hydrogen nebulae of uniform density, and accuracies of the on-the-spot (OTS) approximation are critically examined. For different values of density and spectral types of the central star, we have calculated the degree of ionization and the kinetic temperature of electrons as functions of distance from the central star, and compared them with the corresponding results of the OTS approximation. At most locations inside an HII region. the DFR ionizes considerable amount of hydrogen; therefore, the OTS approximation under-estimates the size of ionized regions. The exact treatment of the DFR transfer results in an about 10 to 20 percent increase in the classical <TEX>$Str{\ddot{o}}mgren$</TEX> radius. The OTS approximation overestimates the local heating rate by raising the density of neutral hydogens. Consequently, it predicts higher values for the local electron temperature. The OTS approximation also exaggerates the dependence of electron temperature on density. When the hydrogen density is changed from <TEX>$10/cm^3$</TEX> to <TEX>$10^3/cm^3$</TEX> with an 06.5V star, the OTS approximation shows an about 3,000 K difference in the electron temperature, while the exact treatment of the DFR-transfer reduces the difference to about 1,000 K. The OTS approximation fails to demonstrate the brightening of the electron temperature close to the ionization boundary.
1056
- Lee, Sang-Gak
- 天文學會誌 = The journal of the Korean Astronomical Society
- 22, n.2
- pp.101-111
- 1989
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We have analysed the proper motion data of LHS catalog, to derive the faint end of the luminosity function more precise than ever before, by mean absolute method, and by making use of the reudced proper motion diagram. It is found that the relations between the mean absolute magnitude and the reduced proper motion for main sequence stars, subdwarfs, and white dwarfs are so different that the proper application of an appropriate relation to each group is much more important. The derived luminosity function shows the broad maximum peak from <TEX>$M_B{\sim}14$</TEX> to <TEX>$M_B{\sim}17$</TEX> and declines after <TEX>$M_B{\sim}17$</TEX> up to <TEX>$M_B{\sim}22$</TEX>.
1057
- Kim, K.T.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 22, n.1
- pp.25-30
- 1989
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We report a null detection of <TEX>$^{12}CO$</TEX> emission from a sub-condensation in a High Velocity Cloud (HVC). As a consequence of this, an upper limit of <TEX>$n(H_2)\frac{X(CO)}{DV/DR}{\leq}2{\times}10^{-5}$</TEX> was set. This implies that <TEX>$^{12}CO$</TEX> abundance is deficient by at least a factor of 10 if the HVC is predominantly molecular, otherwise the CO abundance of the HVC might be normal.
1058
- Whang, Yun-Oh
- 天文學會誌 = The journal of the Korean Astronomical Society
- 22, n.1
- pp.1-24
- 1989
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By applying population synthesis method, stellar populations in the nuclei of M31 and M32 are studied. We obtained five and four models for M31 and M32 respectively, for different main sequence turn-offs and keeping the astrophysical constraints as loose as possible. The best models for M31 and M32 are thought to have G0-5 and F5-8 main sequence trun-offs respectively. These models show that the main sequence stars outnumber the giants, which indicates the dwarf-dominance in external galactic nuclei. Even though there are some computational difficulties because of non-uniqueness in solution, two major points can be pointed out when compared to the previous papers. First, the ultraviolet deficiency expected from the conventional metal rich population models is not detected in our models, Instead ultraviolet radiation turns out to be somewhat higher than that of observation. Second one is the minor contribution from the Super Metal Rich (SMR) K giants to the integrated light of the program galaxies. That is, in our models, the SMR contribution is at best the same level as normal giants contrary to the SMR dominance of previous models. Since the loose astrophysical constraints are the major difference of our study from the previous ones, one should re-examine carefully for their validity further.
1059
- Lee, See-Woo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 22, n.1
- pp.43-61
- 1989
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The ages of field stars given in the catalogue of Cayrel de Strobel et al. (1985) are derived by the five different methods with combination of theoretical isochrones. By using these ages and metal abundances homogenized by Lee and Choe (1988), the age-metallicity relations are obtained. For disk stars of [Fe/H] > -0.9, the present age-metallicity relations are nearly consistent with those given by Twarog (1980) and Carlberg et al. (1985).
1060
- Lee, Yoo-Mi
- 天文學會誌 = The journal of the Korean Astronomical Society
- 22, n.1
- pp.31-41
- 1989
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Luminosity profile of the late type spiral galaxy NGC 2403 was obtained using the PDS scan of the plate. Some physical parameters (scale length, total magnitude, central brightness, disk to bulge ratio and concentric indices) were calculated from the brightness distribution. Total mass and the mass to luminosity ratio were estimated from the fitting of various mass models.