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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 111/122
1101
- Lee, Jeong-Woo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 20, n.1
- pp.27-47
- 1987
- 원문 바로보기
In the present study a two-mode, separately concurring resonant cavity model is proposed for theoretical interpretation of the 3 minute umbral oscillation. The proposed model has been investigated by calculating the transmission coefficients of the waves propagating through the umbral photosphere (photospheric weak-field cavity) and chromosphere (chromospheric strong-field cavity) into the corona, for 3 different umbral model atmospheres by Staude (1982), Beebe et al. (1982) and Avrett (1981). In computing the transmission coefficients we made use of multi-layer approximation by representing the umbra] atmosphere by a number of separate layers with (1) temperature varying linearly with depth and (2) temperature constant within each layer. The medium is assumed to be compressible, non-viscous, perfectly conducting under gravity. The computed resonant periods, transmission spectra, phase spectra, and kinetic energy density of the waves associated with the oscillations are presented in comparison with the observations and their model dependent characteristics are discussed.
1102
- Lee, Jeong-Woo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 20, n.2
- pp.95-95
- 1987
- 원문 바로보기
1103
- Ann, Hong-Sik
- 天文學會誌 = The journal of the Korean Astronomical Society
- 20, n.2
- pp.49-62
- 1987
- 원문 바로보기
Using the detailed two-dimensional surface photometry of 39 galaxies, the observed profiles are decomposed into spheroid, disk and bar components simultaneously. From the analyses of decomposition parameters, the correlations among the three components are investigated to find the global property of barred galaxies. And the lens and ring components, and spiral arm patterns are also examined with Hubble type and decomposition parameters.
1104
- Ann, Hong-Bae
- 天文學會誌 = The journal of the Korean Astronomical Society
- 19, n.2
- pp.69-89
- 1986
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The global morphology and geometric parameters of 39 barred galaxies are investigated, by using isophote map and isodensity tracings obtained from detailed surface photometry with the Kiso V-band plates. The observed results are as follows: i) There is no strong indication that the ratio of bar length to disk size is correlated with Hubble type, except that the largest bars appear in the SBb galaxies. ii) The mean value of axial ratios of bars is <TEX>$2.0{\pm}0.4$</TEX> and there is a trend that early type galaxies have smaller axial ratios than late type galaxies. iii) About 15% of early type barred galaxies(Sb0-SBb) have triaxial bulges.
1105
- Park, Yong-Sun
- 天文學會誌 = The journal of the Korean Astronomical Society
- 19, n.1
- pp.15-31
- 1986
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We have analyzed Gray's observed mean line bisectors of FS, G0, G2, and G5 normal dwarf stars and interpreted them by computing theoretical line bisectors based on a two stream model. A set of perturbed models has been derived, and their detailed structures on temperature fluctuations and velocity fields are presented as a function of depth, which account for the observed bisectors. From the present study, it is found that the degree of stellar convective overshootings and temperature fluctuations in the upper atmospheres increases towards earlier spectral types. The convection cell size inferred from these models is found to increase also with the advancing earlier type. We demonstrated the usefulness of line bisector analysis as a diagnostic probe for stellar convection.
1106
- Yoo, Chin-Woo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 19, n.1
- pp.33-49
- 1986
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Radial distribution of internal density has been determined for thirteen subclouds in the three giant molecular cloud complexes accompanying Mon OB1, Mon OB2 and CMa OB1 associations, We modeled their radial density structures with the density distribution of isothermal gas spheres. Most of the subclouds, nine out of the thirteen, are well described by isothermal spheres of single component; while the rest four require an additional component. Total mass and potential energy of each subcloud are also derived from the radial density structure; thermal energy and internal velocity dispersion required for sustaining the density structure are deduced from the isothermal gas model. Our derived masses of the clouds are comparable to the values determined by Blitz (1978) under LTE assumption. This agreement suggests that the correction factor for non-LTE effect on mass-estimate is not far from unity. The ratio of the gravitational potential energy to the kinetic energy of thermal motion is as large as 250; hence the thermal motion alone cannot support these clouds against the gravity. Being supported by turbulence motion with velocities of six to seven times the thermal velocity, the clouds of one-component type seem to be in equilibrium with the gravity; while the clouds of two-component type are likely to be in the stage of gravitational collapse.
1107
- Chang, Kyong-Ae
- 天文學會誌 = The journal of the Korean Astronomical Society
- 19, n.2
- pp.63-68
- 1986
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In this paper we deal with the orientation and the deformation of the circular light bundle passing in a static bounded gravitational field. The properties of caustic of the gravitational lens are discussed.
1108
- Park, Chang-Bum
- 天文學會誌 = The journal of the Korean Astronomical Society
- 19, n.2
- pp.91-107
- 1986
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Making use of our extended version of <TEX>$\ddot{O}pik's$</TEX> convection theory, we have calculated magnetic cycle periods of the sun and late type stars by using Parker's dynamo theory, where we have included the non-linear effect. We presented a relationship between the computed cycle period and spectral type to analyze observed magnetic activities of the late type stars and long-term luminosity variations. It is found that (1) the stellar magentic-cycle period increases towards the later spectral type, (2) the rapid rotation facilitates the activity-related luminosity variation of stars later than about K5, (3) differential rotation plays a critical role in determining the magnetic activity-cycle period, and (4) the non-local effect should be taken into account in order to understand the observed long-term luminosity variations.
1109
- Lee, See-Woo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 19, n.2
- pp.51-62
- 1986
- 원문 바로보기
The Wielen dip over the ragne of 6 < <TEX>$M_{\upsilon}$</TEX> < 9 in the luminosity function (LF) for the solar neighborhood stars could be explained by the combination of two different IMFs which yields the age of 13 billion years of the solar neighborhood. This smaller age than the Galactic age, 15 billion years indicates the slow collapse model of the Galaxy, solving the G-dwarf problem. Two different IMFs suggest two different mechanisms for star formation in the solar neighborhood.
1110
- Chang, Kyong-Ae
- 天文學會誌 = The journal of the Korean Astronomical Society
- 19, n.1
- pp.11-14
- 1986
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It is shown in this paper that the astigmatic property of single gravitational lens in static bounded gravitational field can be retained, if n-gravitating body as a whole acts simultaneously as gravitational lens.