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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 109/123
1081
- 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.
1082
- Park, Seok-Jae
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.2
- pp.116-121
- 1990
- 원문 바로보기
It has been suggested that there could be a large number of primordial black holes which were formed in the early universe. We analyze the growth of such a primordial black hole following two different accretion rates - the Eddington accretion rate and the Bondi accretion rate - at the center of a host star like the sun. We find that a primordial black hole with M < <TEX>${\sim}10^{17}\;g$</TEX> cannot substantially grow in any case throughout the lifetime of a host star. If M > <TEX>${\sim}10^{17}\;g$</TEX>, the evolution of a host star depends entirely on the mode of accretion, but it ends as a black hole in either case. Since more stars may have primordial black holes at the center of a galaxy this may result in a cluster of such black holes, and the cluster may eventually collapse to produce a single supermassive black hole.
1083
- Lee, Hyung-Mok
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.2
- pp.97-105
- 1990
- 원문 바로보기
The tidal radii of globular clusters reflect the tidal field of the Galaxy. The mass distribution of the Galaxy thus may be obtained if the tidal fields of clusters are well known. Although large amounts of uncertainties in the determination of tidal radii have been obstacles in utilizing this method, analysis of tidal density could give independent check for the Galactic mass distribution. Recent theoretical modeling of dynamical evolution including steady Galactic tidal field shows that the observationally determined tidal radii could be systematically larger by about a factor of 1.5 compared to the theoretical values. From the analysis of entire sample of 148 globular clusters and 7 dwarf spheroidal systems compiled by Webbink (1985), we find that such reduction from observed values would make the tidal density (the mean density within the tidal radius) distribution consistent with the flat rotation curve of our Galaxy out to large distances if the velocity distribution of clusters and dwarf spheroidals with respect to the Galactic center is isotropic.
1084
- Park, Seok-Jae
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.1
- pp.63-70
- 1990
- 원문 바로보기
The original axisymmetric, stationary electrodynamic model of the central engine in an active galactic nucleus proposed by Macdonald and Thorne consists of a supermassive black hole with magnetic field lines that pass through the region just outside the event horizon of the black hole. Each magnetic field line rotates with a constant angular velocity which will exceed the speed of light at large radii. Even though the field lines are purely mathematical entities this condition sets a stringent physical constraint on the motion of the magnetic field lines and the particles on them. In this paper we will show that we can remove this auxiliary constraint in our model by allowing nonstationary processes. As a result the magnetic field lines can be twisted and wound up in a region lying outside of the quasi-stationary magnetosphere of the black hole. We conclude that astrophysical jets are formed in that region due to the twisted and wound magnetic field lines powered by the Blandford-Znajek process and the other driving forces.
1085
- Lee, Sang-Gak
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.1
- pp.83-84
- 1990
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1086
- 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.
1087
- Cho, Se-Hyung
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.2
- pp.85-96
- 1990
- 원문 바로보기
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.
1088
- 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.
1089
- 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.
1090
- Kim, Seoung-Li
- 天文學會誌 = The journal of the Korean Astronomical Society
- 23, n.1
- pp.1-13
- 1990
- 원문 바로보기
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.