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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 75/122
741
- 유계화
- Journal of the Korean astronomical society = 천문학회지
- 33, n.3
- pp.173-175
- 2000
- 원문 바로보기
The time-dependence of an <TEX>$\alpha$</TEX>-disk model under the influence of collisions of particles is examined. Collisions with viscosity tend to take away angular momentum. Both effects cause the disk to rotate more rapidly. The disk gradually contracts with increasing time.
742
- AHN SANG-HYEON
- Journal of the Korean astronomical society = 천문학회지
- 33, n.1
- pp.29-36
- 2000
- 원문 바로보기
We developed a Monte Carlo code that describes the resonant Ly<TEX>$\alpha$</TEX> line transfer in an optically thick, dusty, and static medium. The code was tested against the analytic solution derived by Neufeld (1990). We explain the line transfer mechanism by tracing histories of photons in the medium. We find that photons experiences a series of wing scatterings at the moment of thier escape from the medium, during which polarization may develop. We examined the amount of dust extinction for a wide range of dust abundances, which are compared with the analytic solution. Brief discussions on the astrophysical application of our work are presented.
743
- BONG SU-CHAN
- Journal of the Korean astronomical society = 천문학회지
- 33, n.3
- pp.159-163
- 2000
- 원문 바로보기
We have investigated one dimensional steady flow model of a typical magnetic flux tube in the solar transition region constrained to observed Differential Emission Measure (DEM) for the average quiet-Sun deduced by Raymond & Doyle (1981) with a flux tube geometry conforming to Doppler shifts of UV lines measured by Chae, Yun & Poland (1998). Because local heating and filling factor in the transition region are not well known, we considered two extreme cases, one characterized by the filling factor= 1 ('filled-up model') and the other set by local heating=0 ('not-heated model'). We examined how much the heating is required for the flux tube by recomputing a model through adjustment of the filling factor in such a way that 'not-heated model' accounts for the observed DEM.
744
- LEE YOUNG SUN
- Journal of the Korean astronomical society = 천문학회지
- 33, n.3
- pp.165-172
- 2000
- 원문 바로보기
A baffle system for an airglow photometer, which will be on board the Korea Sounding Rocket-III(KSR-III), has been designed to suppress strong solar scattered lights from the atmosphere below the earth limb. Basic principles for designing a baffle system, such as determination of baffle dimensions, arrangement of vanes inside a baffle tube, and coating of surfaces, have been reviewed from the literature. By considering the constraints of the payload size of the KSR-III and the incident angle of solar light scattered from the earth limb, we first determined dimensions of a two-stage baffle tube for the airglow photometer. We then calculated positions and heights of vanes to prohibit diffusely reflected lights inside the baffle tube from entering into the photometer. In order to evaluate performance of the designed baffle system, we have developed a ray tracing program using a Monte Carlo method. The program computed attenuation factors of the baffle system on the order of <TEX>$10^{-6}$</TEX> for angles larger than <TEX>$10^{\circ}$</TEX>, which satisfies the requirements of the KSR-III airglow experiment. We have also measured the attenuation factors for an engineering model of the baffle system with a simple collimating beam apparatus, and confirmed the attenuation factors up to about <TEX>$10^{-4}$</TEX>. Limitation of the apparatus does not allow to make more accurate measurements of the attenuation factors.
745
- KANG HYESUNG
- Journal of the Korean astronomical society = 천문학회지
- 33, n.2
- pp.111-121
- 2000
- 원문 바로보기
Many models of globular cluster formation assume the presence of cold dense clouds in early universe. Here we re-examine the Fall & Rees (1985) model for formation of proto-globular cluster clouds (PGCCs) via thermal instabilities in a protogalactic halo. We first argue, based on the previous study of two-dimensional numerical simulations of thermally unstable clouds in a stratified halo of galaxy clusters by Real et al. (1991), that under the protogalactic environments only nonlinear (<TEX>${\delta}{\ge}1$</TEX>) density inhomogeneities can condense into PGCCs without being disrupted by the buoyancy-driven dynamical instabilities. We then carry out numerical simulations of the collapse of overdense douds in one-dimensional spherical geometry, including self-gravity and radiative cooling down to T = <TEX>$10^4$</TEX> K. Since imprinting of Jeans mass at <TEX>$10^4$</TEX> K is essential to this model, here we focus on the cases where external UV background radiation prevents the formation of <TEX>$H_2$</TEX> molecules and so prevent the cloud from cooling below <TEX>$10^4$</TEX> K. The quantitative results from these simulations can be summarized as follows: 1) Perturbations smaller than <TEX>$M_{min}\~(10^{5.6}\;M{\bigodot})(nh/0.05cm^{-3})^{-2}$</TEX> cool isobarically, where nh is the unperturbed halo density, while perturbations larger than <TEX>$M_{min}\~(10^8\;M{\bigodot})(nh/0.05cm^{-3})^{-2}$</TEX> cool isochorically and thermal instabilities do not operate. On the other hand, intermediate size perturbations (<TEX>$M_{min} < M_{pgcc} < M_{max}$</TEX>) are compressed supersonically, accompanied by strong accretion shocks. 2) For supersonically collapsing clouds, the density compression factor after they cool to <TEX>$T_c = 10^4$</TEX> K range <TEX>$10^{2.5} - 10^6$</TEX>, while the isobaric compression factor is only <TEX>$10^{2.5}$</TEX>. 3) Isobarically collapsed clouds (<TEX>$M < M_{min}$</TEX>) are too small to be gravitationally bound. For supersonically collapsing clouds, however, the Jeans mass can be reduced to as small as <TEX>$10^{5.5}\;M_{\bigodot}(nh/0.05cm^{-3})^{-1/2}$</TEX> at the maximum compression owing to the increased density compression. 4) The density profile of simulated PGCCs can be approximated by a constant core with a halo of <TEX>$p{\infty} r^{-2}$</TEX> rather than a singular isothermal sphere.
746
- MINH Y. C.
- Journal of the Korean astronomical society = 천문학회지
- 33, n.1
- pp.37-45
- 2000
- 원문 바로보기
We have investigated the properties of the high-latitude cloud MBM 7 using the 3 mm transitions of CO, CS, HCN, <TEX>$HCO^+,\;C_3H_2,\;N_2H^+$</TEX>, and SiO. The molecular component of MBM 7 shows a very clumpy structure with a size of <TEX>$\le$</TEX>0.5 pc, elongated along the northwest-southeast direction, perpendicularly to an extended HI component, which could be resulted from shock formation. We have derived physical properties for two molecular cores in the central region. Their sizes are 0.1-0.3 pc and masses 1-2 M<TEX>$\bigodot$</TEX> having an average volume density <TEX>$\~2{\times}10^3 cm^{-3}$</TEX> at the peak of molecular emission. We have tested the stability of the cores using the full version of the virial theorem and found that the cores are stabilized with ambient medium, and they are expected not to be dissipated easily without external perturbations. Therefore MBM 7 does not seem to be a site for new star formation. The molecular abundances in the densest core appear to be much less (by about one order of magnitude) than the 'general' dark cloud values. If the depletions of heavy elements are not significant in the HLCs compared with those in typical dark clouds, our results may suggest different chemical evolutionary stages or different chemical environments of the HLCs compared with dense dark clouds in the Galactic plane.
747
- MOON Y.-J.
- Journal of the Korean astronomical society = 천문학회지
- 33, n.2
- pp.123-126
- 2000
- 원문 바로보기
We have developed a near real-time flare alerting system which (1) downloads the latest GOES-l0 1-8 <TEX>${\AA}$</TEX> X-ray flux 1-min data by an automated ftp program and shell scripts, (2) produces a beep sound in a simple IDL widget program when the flux is larger than a critical value, and (3) makes it possible to do a wireless alerting by a set of portable transceivers. Thanks to the system, we have made successful Ha flare observations by the Solar Flare Telescope in Bohyunsan Optical Astronomy Observatory. This system is expected to be helpful for ground-based flare observers.
748
- LEE SANG-GAK
- Journal of the Korean astronomical society = 천문학회지
- 33, n.3
- pp.137-142
- 2000
- 원문 바로보기
CN and CH band strengths for ten new bright giants in the globular cluster M15 have been measured from archival spectra obtained with the Multiple Mirror Telescope. Using published indices for other bright M15 giants, a CN-CH band strength anticorrelation is found for bright red giants. However, stars that do not follow the CN-CH anticorrelation are also found. They seem to show a positive correlation between the two indices. Among them, all the AGB and HB stars of the sample are included. Stars I-38 and X6, which are located near the RGB fiducial line in the CMD, have low measured CH(G) indices compared with other RGB stars. Stars IV-38, S4, and S1, which are all near the RGB tip, have strong measured CH(G) indices. Therefore, most of their evolutionary states are suspected to be different from those of a normal single RGB star.
749
- HYUNG SIEK
- Journal of the Korean astronomical society = 천문학회지
- 33, n.2
- pp.81-88
- 2000
- 원문 바로보기
The international ultraviolet explorer (IUE) spectra of a low dispersion <TEX>$\~6{\AA}$</TEX>, have been investigated for two Seyfert 1 galaxies, Mrk 335 and NGC 4051, well known for the line variability. The electron densities of broad line region (BLR) of these variable Seyfert 1 galaxies have been derived, which showed a non-linear abrupt variation from <TEX>$10^8$</TEX> to <TEX>$10^{10} cm-3$</TEX> within a month. We also found the excitation (or temperature) changes in the Mrk 335 BLR from the IUE broad line profiles analysis, but no such evidence in the NGC 4051. The large amount of mass inflow activity through the bar or spiral structure of host galaxies, may trigger the density change in BLR and emission line variability for both objects. Mass of the giant black holes appear to be order of <TEX>$10^7\;M_{\bigodot}$</TEX> for both variable Seyfert l's.
750
- ANN HONG BAE
- Journal of the Korean astronomical society = 천문학회지
- 33, n.1
- pp.1-17
- 2000
- 원문 바로보기
We have performed extensive simulations of response of gaseous disk in barred galaxies using SPH method. The gravitational potential is assumed to be generated by disk, bulge, halo, and bar. The mass of gaseous disk in SPH simulation is assumed to be negligible compared to the stellar and dark mass component, and the gravitational potential generated by other components is fixed in time. The self-gravity of the gas is not considered in most simulations, but we have made a small set of simulations including the self-gravity of the gas. Non-circular component of velocity generated by the rotating, non-axisymmetric potential causes many interesting features. In most cases, there is a strong tendency of concentration of gas toward the central parts of the galaxy. The morphology of the gas becomes quite complex, but the general behavior can be understood in terms of simple linear approximations: the locations and number of Lindblad resonances play critical role in determining the general distribution of the gas. We present our results in the form of 'atlas' of artificial galaxies. We also make a brief comment on the observational implications of our calculations. Since the gaseous component show interesting features while the stellar component behaves more smoothly, high resolution mapping using molecular emission line for barred galaxies would be desirable.