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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
- 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.
1072
- Shin, Jong-Yeob
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.1
- pp.15-29
- 1990
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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.
1073
- 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.
1074
- Kim, Seoung-Li
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.1
- pp.1-13
- 1990
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New uvby photoelectric photometry was carried out for a <TEX>$\delta$</TEX> Scuti variable, HR1170. By applying the Fourier method and the linear least square method, three frequencies were derived: <TEX>$f_1=10.06134c/d$</TEX> (<TEX>$P_1=0.^d0994$</TEX>). <TEX>$f_2=11.91754c/d$</TEX> (<TEX>$P_2=0.^d0839$</TEX>). <TEX>$f_3=18.96776c/d$</TEX> (<TEX>$P_3=0.^d0527$</TEX>). From the observed pulsational constants and from the phase difference and amplitude ratios for color(b-y) and magnitude y. three different pulsation modes (n, l) of <TEX>$f_1(0,0)$</TEX>, <TEX>$f_2(1,2)$</TEX>, <TEX>$f_3(3,2)$</TEX> are deduced, indicating the existence of nonradial mode in HR1170. Some physical parameters indicate that HR1170 is evolving at the stage of H-shell burning.
1075
- Kim, Kap-Sung
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.1
- pp.71-82
- 1990
- 원문 바로보기
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.
1076
- 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.
1077
- 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.
1078
- 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.
1079
- 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.
1080
- 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.