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- The Korean Astronomical Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-4614 (ISSN : 1225-4614)
1225-4614
- DB구축현황 : 1,227건 (DB Construction : 1,227 Articles)
총 게시글 1,227건
페이지 110/123
1091
- Kim, Kap-Sung
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.1
- pp.71-82
- 1990
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Theoretical calculations of the combined radiative transfer and statistical equilibrium equation including the charge-particle conservations have been earned out for a multilevel hydrogen atom in quiescent prominences. Cool and dense models show the steep changes of population and radiation field in the vicinity of the surface, while these physical quantities remain unchanged for models with temperature of 7,300K, regardless of total densities. Ionization rate of hydrogen atom related with metallic line formation varies in considerable amounts from the surface to the center of model prominences cooler than 6,300K. However, such cool models cannot release enough hydrogen line emissions to explain observed intensities. Prominence models with a temperature higher than 8,000K can yield the centrally reversed Lyman line profiles confirmed by satellite EUV observations. We find that queiscent prominence with a density between <TEX>$2{\times}10^{11}$</TEX> and <TEX>$10^{12}cm^{-3}$</TEX> should be in temperature range between 6,300K and 8,300K, in order to explain consistently observed H alpha, beta line emissions and <TEX>$n_p/n_l$</TEX> ratio.
1092
- Park, Hong-Suh
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.2
- pp.106-111
- 1990
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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.
1093
- 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.
1094
- 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.
1095
- 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.
1096
- Hong, S.S.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 22, n.1
- pp.63-79
- 1989
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Current estimates, based on the same star-count analysis, of the distance to the globule Bamard 361 range from 300 pc to 650 pc. All the problems associated with the estimates have been fully rectified in this study, and a modification has been made to the classical Wolf diagram to improve the accuracy in the distance determination. A reference field was carefully selected close to the globule but well outside the globule boundary, and star counts for this field were performed on the blue POSS plate in order to set up the reference magnitude sequence appropriate to the general area of B 361. From the reference sequence, the stellar density function has been derived specifically for the direction toward the globule. Correction was made for the general interstellar extinction, and the luminosity function with the Wielen's dip was adopted. The resulting density function clearly reveals the existence of the local Cygnus-Orion arm in the direction of B 361 at about 700 pc away from the Sun. Analysis of the star-count data for the program field locates the globule at distance <TEX>$600{\pm}50$</TEX> pc ; thus, the globule is an object located in the Cygnus-Orion arm, residing somewhat toward its leading edge.
1097
- 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).
1098
- Kwon, Suk-Min
- 天文學會誌 = The journal of the Korean Astronomical Society
- 22, n.2
- pp.141-160
- 1989
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In order to derive time dependence of the atmospheric diffuse light, which consists of the airglow continuum emission and diffusely scattered radiations of the intergrated starlight, the diffuse Galactic light, and the zodiacal light, we have analyzed the meridian scan observations of the sky brightness at <TEX>$5,080\;{\AA}$</TEX> and <TEX>$5,300\;{\AA}$</TEX>. Amplitude of the time-variation becomes larger for lower elevation, and maximum amplitude is found to be about <TEX>$50\;S_{10}(V)_{G2V}$</TEX> at elevation <TEX>$10^{\circ}$</TEX>. The atmospheric diffuse radiation attains maximum brightness at around midnight, and afterward it decreases slowly with time. The time-variations for the two wavelengths are similar to each other. The observed brightness distribution of the diffuse light along the zenith distance is fitted to an empirical relation of two parameters. By making the two parameters time-dependent, we describe the spatial and time variations of the atmospheric diffuse light. This enables us to make time dependent correction for the atmospheric diffuse component in the reduction of zodiacal light brightness.
1099
- 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.
1100
- 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.