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1968년 ~ 2024년까지 1,211 건의 한국천문학회지를 격월간 확인하실 수 있습니다.
- 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 102/122
1011
- LA DAILE
- Journal of the Korean astronomical society = 천문학회지
- 28, n.1
- pp.67-70
- 1995
- 원문 바로보기
In contrast to conventional belief that extended inflation ends when the Universe percolates, we find inflation may continue at least many Hubble times even after the Universe percolates. What is observed is that inflation will not stop unless the global equation of state changes from inflationary one into radiation one. Thus the energy density of shorter wavelength gravitational waves induced by bubble collision at near the end of inflation should be at least Order <TEX>$(10^2)\~O(10^3)$</TEX> times greater than previous estimation of Turner and Wilcek(TW).
1012
- LEE SANG-WOO
- Journal of the Korean astronomical society = 천문학회지
- 28, n.1
- pp.77-87
- 1995
- 원문 바로보기
An attempt has been made to analyze time series of <TEX>$H_\alpha,\;H_\beta,\;and\; H_\gamma$</TEX> line profiles taken from a 3B/X6.1 flare which occurred on Oct. 27, 1991 in an active region, NOAA 6891. A total of 22 sets of <TEX>$H_\alpha,\;H_\beta,\;and\; H_\gamma$</TEX> taken with a low and non-uniform time resolution of 10-40 seconds were scanned by PDS with absolute intensity calibration to derive the physical characteristics of the material in the flare chromosphere. Our . results are as follows: (1) The lower Balmer lines observed during the flare activity are broadened by Stark effect. (2) At the peak of the flare activity, the electron temperature of the Balmer line emitting region reaches up to 35000K and its geometrical thickness increases to a scale of <TEX>$10^4km$</TEX>, suggesting that high energy particles penetrate deep into the photospheric level.
1013
- Ryu, Dong-Su
- Journal of the Korean astronomical society = 천문학회지
- 28, n.2
- pp.223-243
- 1995
- 원문 바로보기
We describe the implementation of a multi-dimensional numerical code to solve the equations for idea! magnetohydrodynamics (MHD) in cylindrical geometry. It is based on an explicit finite difference scheme on an Eulerian grid, called the Total Variation Diminishing (TVD) scheme, which is a second-order-accurate extension of the Roe-type upwind scheme. Multiple spatial dimensions are treated through a Strang-type operator splitting. Curvature and source terms are included in a way to insure the formal accuracy of the code to be second order. The constraint of a divergence-free magnetic field is enforced exactly by adding a correction, which involves solving a Poisson equation. The Fourier Analysis and Cyclic Reduction (FACR) method is employed to solve it. Results from a set of tests show that the code handles flows in cylindrical geometry successfully and resolves strong shocks within two to four computational cells. The advantages and limitations of the code are discussed.
1014
- MOON DAE-SIK
- Journal of the Korean astronomical society = 천문학회지
- 27, n.1
- pp.81-102
- 1994
- 원문 바로보기
We have decomposed the 11-cm radio continuum emission of the W51 complex into thermal and non-thermal components. The distribution of the thermal emission has been determined by analyzing HI, CO, and IRAS <TEX>$60-{\mu}m$</TEX> data. We have found a good correlation between the 11-cm thermal continuum and the 60- 11m emissions, which is used to obtain the thermal and non-thermal 11-cm continuum maps of the W51 complex. Most of the thermal continuum is emanating from the compact H II regions and their low-density ionized envelopes in W51A and W51B. All the H II regions, except G49.1-0.4 in W51B, have associated molecular clumps. The thermal radio continuum fluxes of the compact H II regions are proportional to the CO fluxes of molecular clumps. This is consistent with the previous results that the total mass of stars in an H II region is proportional to the mass of the associated molecular clump. According to our result, there are three non-thermal continuum sources in W51: G49.4-0.4 in W51A, a weak source close to G49.2-0.3 in W51B, and the shell source W51C. The non-thermal flux of G49.5-0.4 at 11-cm is <TEX>$\~28 Jy$</TEX>, which is <TEX>$\~25\%$</TEX> of its total 11-cm flux. The radio continuum spectrum between 0.15 and 300 GHz also suggests an excess emission over thermal free-free emission. We show that the excess emission can be described as a non-thermal emission with a spectral index <TEX>${\alpha}{\simeq}-1.0 (S_v{\propto}V^a)$</TEX> attenuated by thermal free-free absorptions at low-frequencies. The non-thermal source close to G49.2-0.3 is weak <TEX>$(\~9 Jy)$</TEX>. The nature of the source is not known and the reality of the non-thermal emission needs to be confirmed. The non~thermal shell source W51C has a 11-cm flux of <TEX>$\~130Jy$</TEX> and a spectral index <TEX>${\alpha}{\simeq}-0.26$</TEX>.
1015
- JUNG HEE
- Journal of the Korean astronomical society = 천문학회지
- 27, n.2
- pp.177-190
- 1994
- 원문 바로보기
We have examined the photometric evolution of elliptical galaxies, using stellar evolutionary models covering the wide ranges of metallicity and mass, and the different IMFs (simple IMP & time-dependent bimodal IMF). The model with a time-dependent bimodal IMF can reproduce the observed integrated magnitudes and colors at all wavelengths. The computed model shows that the star formation in elliptical galaxies is still going on, although the number of newly born stars is very small. The chemical evolutionary effect is clearly seen in the C-M diagram of computed elliptical galaxies.
1016
- CHAE JONG-CHUL
- Journal of the Korean astronomical society = 천문학회지
- 27, n.2
- pp.191-201
- 1994
- 원문 바로보기
We propose to use the entropy of power spectra defined in the frequency domain for the deconvolution of extended images. Spatial correlations requisite for extended sources may be insured by increasing the role of power entropy because the power is just a representation of spatial correlations in the frequency domain. We have derived a semi-analytical solution which is found to severely reduce computing time compared with other iteration schemes. Even though the solution is very similar to the well-known Wiener filter, the regularizingng term in the new expression is so insensitive to the noise characteristics as to assure a stable solution. Applications have been made to the IRAS <TEX>$60{\mu}m\;and\;100{\mu}m$</TEX> images of the dark cloud B34 and the optical CCD image of a solar active region containing a circular sunspot and a small pore.
1017
- LEE HYUN-A
- Journal of the Korean astronomical society = 천문학회지
- 27, n.2
- pp.103-117
- 1994
- 원문 바로보기
To extend the work of Gott, Park, and Lee (1989), statistical properties of gravitational lensing in a wide variety of cosmological models involving non-zero cosmological constant is investigated, using the redshifts of both lens and source and observed angular separation of images for gravitational lens systems. We assume singular isothermal sphere as lensing galaxy in homogenous and isotropic FriedmannLemaitre-Robertson- Walker universe, Schechter luminosity function, standard angular diameter distance formula and other galaxy parameters used in Fukugita and Turner (1991). To find the most adequate flat cosmological model and put a limit on the value of dimensionless cosmological constant <TEX>$\lambda_0$</TEX>, the mean value of the angular separation of images, probability distribution of angular separation and cumulative probability are calculated for given source and lens redshifts and compared with the observed values through several statistical methods. When there is no angular selection effect, models with highest value of <TEX>$\lambda_0$</TEX> is preferred generally. When the angular selection effects are considered, the preferred model depends on the shape of the selection functions and statistical methods; yet, models with large <TEX>$\lambda_0$</TEX> are preferred in general. However, the present data can not rule out any of the flat universe models with enough confidence. This approach can potentially select out best model. But at the moment, we need more data.
1018
- PYO TAE SOO
- Journal of the Korean astronomical society = 천문학회지
- 27, n.2
- pp.119-132
- 1994
- 원문 바로보기
The BVR CCD photometry was performed for the globular cluster M13 down to <TEX>$V=19^m$</TEX> over the region from the center to the west 13 arcmin and the CMD of M13 is investigated. The major photometric error in the crowded field which is due to the variation in the sky background was corrected by the median filtering method and the direct sky method. Some characteristics of the CMD of M13 obtained in the present study are as follows: Firstly, the distribution of stars on the CMD is well consistent with the mean lines of Sandage(1970) along the red giant branch(RGB), horizontal branch(HB) and asymtotic giant branch(AGB). Secondly, some gaps exists along the RGB and blue horizontal branch(BHB). Thirdly, the UV-bright stars are more concentrated at the inner region of the cluster.
1019
TIDAL EVOLUTION OF GLOBULAR CLUSTERS: THE EFFECTS OF GALACTIC TIDAL FIELD, DIFFUSION AND BLACK HOLES
- OH KAP SOO
- Journal of the Korean astronomical society = 천문학회지
- 27, n.1
- pp.61-76
- 1994
- 원문 바로보기
We investigate the dynamical evolution of globular clusters under the diffusion, the Galactic tide, and the presence of halo black holes. We compare the results with our previous work which considers the diffusion processes and the Galactic tide. We find the followings: (1) The black holes contribute the expansion of the outer part of the cluster. (2) There is no evidence for dependence on the orbital phase of the cluster as in our previous work. (3) The models of linear and Gaussian velocity distribution for the halo black holes do not show any significant differences in all cases. (4) The perturbation of black holes reduces the number of stars in lower energy regions. (5) There is a significant number of stars with retrograde orbits beyond the cutoff radius especially in the case of diffusion and the perturbation of black holes.
1020
- MINN Y. K.
- Journal of the Korean astronomical society = 천문학회지
- 27, n.1
- pp.31-44
- 1994
- 원문 바로보기
The 4.8GHz formaldehyde absorption line in the dark clouds in M17 and NGC 2024 regions has been mapped. In both nebulae, we detected two <TEX>$H_2CO$</TEX> line components. In M17, the 24km <TEX>$S^{-1}$</TEX> cloud is closely associated with the HII region located in front of the radio continuum source, and the 19km <TEX>$S^{-1}$</TEX> cloud is associated with the visual dark clouds with a larger extent which are closer to us. The 19km <TEX>$S^{-1}$</TEX> cloud has a mass motion approaching to the HII region. In both clouds, a velocity gradient from the north-east to the south-west directions is observed. The linewidth has no variation indicating no collapsing motion. In NGC 2024, the 9km <TEX>$S^{-1}$</TEX> feature is extended along the dark bar in front of the bright nebula and a weak second component at 13km <TEX>$S^{-1}$</TEX> is confined to the immediate vicinity of the radio source. Indications are that the 9km <TEX>$S^{-1}$</TEX> cloud is physically associated with the dark bar and the 13km <TEX>$S^{-1}$</TEX> cloud is located behind the radio source. The angular extent, the column density, and the total mass of the clouds are derived. The radial velocities of other molecular lines observed in these clouds are compared.