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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 108/122
1071
- Park, Hong-Suh
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.2
- pp.106-111
- 1990
- 원문 바로보기
Photoelectric observation in 1984 shows light variation outside eclipses. The effect of the changing ambient temperature on the light curves were studied. Difficulty of studying and unitary, or mean, light curve of AR Lac is stressed.
1072
- Lee, Hae-Shim
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.2
- pp.112-115
- 1990
- 원문 바로보기
We test an evolution of a giant void using an N-body simulation. We find the void expansion is faster than the rest part of the universe and the shape of an isolated aspherical void becomes more spherical as it evolves.
1073
- Cho, Se-Hyung
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.2
- pp.85-96
- 1990
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High resolution <TEX>$^{12}CO$</TEX> observations of the region containing the planetary nebula Hb12 were made with the Nobeyama Radio Telescope. These observations reveal that there is no significant CO emission from Hb 12 itself. Near Hb 12, however, the observed regions show a structure of clustered dark clouds whose physical parameters suggest that these clumps would be further fragmented or collapesed. Also found with the high resolution observations is that a few isolated clumps are located away from the main CO feature extended possibly from the galactic plane. For more detail morphologies and velocity structures of the clumps, especially in relation to the large CO complex to which these are likely to be associated, more observations are substantiated.
1074
- Shin, Jong-Yeob
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.1
- pp.15-29
- 1990
- 원문 바로보기
The magnetic reconnection mechanism is a primary candidate for 'flare' processes in solar coronal regions. Numerical simulations of two-dimensional magnetic reconnection are carried out for four different cases: (1) adiabatic condition with constant resistivity, (2) adiabatic condition with temperature-dependent resistivity, (3) energetics with radiation loss and constant resistivity and (4) energetics with radiation loss and temperature-dependent resistivity. It is found that the thermal instability prompts the magnetic reconnection process, thus increasing the conversion rate of magnetic energy into kinematic energy of the fluid. We demonstrated that the observed microflares can be accounted for by our magnetic reconnection models, when the effects of the radiation loss and the temperature-dependent resistivity are taken into account.
1075
- Kim, Kap-Sung
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.1
- pp.31-42
- 1990
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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.
1076
- Kim, Kyung-Ok
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.1
- pp.43-62
- 1990
- 원문 바로보기
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.
1077
- 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.
1078
- Kim, Kang-Min
- 天文學會誌 = The journal of the Korean Astronomical Society
- 22, n.2
- pp.81-99
- 1989
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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.
1079
- 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.
1080
- Hong, S.S.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 22, n.2
- pp.127-140
- 1989
- 원문 바로보기
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.