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1968년 ~ 2023년까지 1,187 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 : 1,187건 (DB Construction : 1,187 Articles)
총 게시글 1,187건
페이지 67/119
661
- 박명구
- Journal of the Korean astronomical society = 천문학회지
- 34, n.2
- pp.81-97
- 2001
- 원문 바로보기
Since the first proposal by Paczynski, great efforts to detect Galactic dark matter by detecting light variations of stars located in the Magellanic Clouds and Galactic bulge caused by gravitational microlensing have been and are being carried out and more than 1,000 events have been successfully detected. In this paper, we review the progress in the theoretical and experimental progresses in microlensing. We begin with basics of microlensing and summarize the results obtained from the last 8 year observations along with the implications of the results. We also discuss the usefulness of microlensing in other fields of astronomy such as the stellar atmosphere, Galactic binary systems, and extra-solar planets. We finally discuss the problems of the current experiments and the new types of observations that can overcome these problems.
662
- SAAD SOMAYA MOHAMED
- Journal of the Korean astronomical society = 천문학회지
- 34, n.2
- pp.99-109
- 2001
- 원문 바로보기
In the present study we have determined the distance moduli for seven globular clusters M2, M3, Ml0, M12, NGC 2808, NGC 6229, and NGC 6752, whose metallicities are in the range -1.54 < [Fe/H] < -1.10. We have derived distances for them by the main-sequence fitting method using a sample of local subdwarfs, whose accurate parallaxes are taken from the Hipparcos Catalog. The derived distance moduli are 15.52 for M2, 14.98 for M3, 14.23 for Ml0, 14.03 for M12, 15.56 for NGC 2808, 17.34 for NGC 6229, and 13.29 for NGC 6752.
663
- GHOSH K. K.
- Journal of the Korean astronomical society = 천문학회지
- 34, n.1
- pp.9-15
- 2001
- 원문 바로보기
We present the results of optical differential photometry of five blazars [PKS0219+428 (3C66A), PKS 0235+164 (AO 0235+16), H0414+019, PKS 0851+202 (OJ 287) and QSO 1807+698 (3C 371)] that were observed on 7 nights between November 05, 1997 and December 29, 1998, using the B and the V band filters. We have detected microvariations in four blazars (3C66A, AO 0235+16, H04l4+019, and OJ 287). In addition, the light curve of AO 0235+16 has displayed a mini-flare when the brightness of this source was decreasing. Night-to-night variations have also been detected in 3C66A, H04l4+019, and OJ 287. The results of our observations are discussed in the framework of accretion disk phenomena (magnetic flares or hot spots in accretion disks) and jet phenomena (plasma instabilities in jets).
664
- LEE HYESOOK
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.321-323
- 2001
- 원문 바로보기
Compressible, magnetohydrodynamic (MHD) turbulence in two dimension is studied through high-resolution, numerical simulations with the isothermal equation of state. First, hydrodynamic turbulence with Mach number <TEX>$(M)_{rms}\;\~$</TEX>1 is generated by enforcing a random force. Next, initial, uniform magnetic field of various strengths with Alfvenic Mach number Ma <TEX>$\gg$</TEX> 1 is added. Then, the simulations are followed until MHD turbulence is fully developed. Such turbulence is expected to exist in a variety of astrophysical environments including clusters of galaxies. Although no dissipation is included explicitly in our simulations, truncation errors produce dissipation which induces numerical resistivity. It mimics a hyper-resistivity in our second-order accurate code. After saturation, the resulting flows are categorized as SF (strong field), WF (weak field), and VWF (very weak field) classes respectively, depending on the average magnetic field strength described with Alfvenic Mach number, <TEX>$(Ma)_{rms}{\ge}1$</TEX>, <TEX>$(Ma)_{rms}{\~}1$</TEX>, and <TEX>$(Ma)_{rms}{\gg}1$</TEX>. The characteristics of each class are discussed.
665
- SHYUE KEH-MING
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.237-241
- 2001
- 원문 바로보기
Our goal is to present a simple volume-of-fluid type interface-tracking algorithm to compressible two-phase flow in two space dimensions. The algorithm uses a uniform underlying Cartesian grid with some cells cut by the tracked interfaces into two subcells. A volume-moving procedure that consists of two basic steps: (1) the update of volume fractions in each grid cell at the end of the time step, and (2) the reconstruction of interfaces from discrete set of volume fractions, is employed to follow the dynamical behavior of the interface motion. As in the previous work with a surface-tracking procedure for general front tracking (LeVeque & Shyue 1995, 1996), a high resolution finite volume method is then applied on the resulting slightly nonuniform grid to update all the cell values, while the stability of the method is maintained by using a large time step wave propagation approach even in the presence of small cells and the use of a time step with respect to the uniform grid cells. A sample preliminary numerical result for an underwater explosion problem is shown to demonstrate the feasibility of the algorithm for practical problems.
666
- KOIDE SHINJI
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.215-224
- 2001
- 원문 바로보기
We present the whole basis of numerical method and useful formulae for general relativistic magnetohydrodynamic simulations in Kerr space-time.
667
- KANG HYESUNG
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.293-295
- 2001
- 원문 바로보기
A numerical scheme that incorporates a self-consistent cosmic-ray (CR, hereafter) injection model into the combined gas dynamics and CR diffusion-convection code has been developed. The hydro/CR code can follow in a very cos-effective way the evolution of CR modified shocks by adopting subzone shock-tracking and multi-level Adaptive Mesh Refinement techniques. The injection model is based on interactions of the suprathermal particles with self-generated MHD waves in quasi-parallel shocks. The particle injection is followed numerically by filtering the diffusive flux of suprathermal particles across the shock to upstream region according to a velocity-dependent transparency function, which represents the fraction of leaking suprathermal particles. In the strong shock limit of Mach numbers <TEX>$\ge$</TEX>20, significant physical processes such as the injection and acceleration seem to become independent of M, while they are sensitively dependent on M for M < 10. Although some particles injected early in the evolution continue to be accelerated to higher energies, the postshock CR pressure reaches a time asymptotic value due to balance between acceleration and diffusion of the CR particles.
668
- SOHN JUNGJOO
- Journal of the Korean astronomical society = 천문학회지
- 34, n.1
- pp.17-24
- 2001
- 원문 바로보기
We have studied the central parts of M82, which is a well-known infrared luminous, starburst galaxy, by analyzing archival data from the Infrared Space Observatory (ISO). M82 was observed at 11 positions covering <TEX>$\pm$</TEX>45' from the center along the major axis. We analyzed 4 emission lines, [ArIII] 8.99 <TEX>${\mu}m$</TEX>, <TEX>$H_2$</TEX> 17.034 <TEX>${\mu}m$</TEX>, [FeII] 25,98 <TEX>${\mu}m$</TEX>, and [SiII] 34,815 <TEX>${\mu}m$</TEX> from <TEX>$SWSO_2$</TEX> data. The integrated flux distributions of these lines are quite different. The <TEX>$H_2$</TEX> line shows symmetric twin peaks at <TEX>$\~$</TEX>18' from the center, which is a general characteristic of molecular lines in starburst or barred galaxies. This line appears to be associated with the rotating molecular ring at around <TEX>$\~$</TEX>200 pc just outside the inner spiral arm. The relative depletion of the <TEX>$H_2$</TEX> line at the center may be due to the active star formation activity which dissociates the <TEX>$H_2$</TEX> molecules. The other lines have peaks at the center and the distributions are nearly symmetric. The line profiles are deconvolved assuming that both intrinsic and instrumental profiles are Gaussian. The velocity dispersion outside the core is found to be <TEX>$\~50 km s^{-1}$</TEX>. The central velocity dispersion is much higher than <TEX>$50 km s^{-1}$</TEX>, and different lines give different values. The large central velocity dispersion (<TEX>$\sigma$</TEX>) is mostly due to the rotation, but there is also evidence for a high <TEX>$\sigma$</TEX> for [ArIII] line. We also generated position-velocity maps for these four lines. We found very diverse features from these maps.
669
- LEE HYUN KYU
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.301-303
- 2001
- 원문 바로보기
We suggest a possible scenario of an astrophysical black hole with non-vanishing electric charge and magnetic flux. The equilibrium charge on a rotating black hole in a force-free magnetosphere is calculated to be Q <TEX>$\~$</TEX> BJ with a horizon flux of <TEX>${\~}BM^2$</TEX>, which is not large enough to disturb the background Kerr geometry. Being similar to the electric charge of a magnetar, in sign and order of magnitude, both electric charge and magnetic flux are supposed to be continuous onto a black hole.
670
- JONES T. W.
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.231-235
- 2001
- 원문 바로보기
Cosmic-ray acceleration, although physically important in many astrophysical contexts, is difficult to incorporate into numerical models,. because it involves microphysics that is generally far from thermodynamic equilibrium, and also because the length and time scales for that physics typically range over many orders of magnitude, reflecting the huge range of particle rigidities that must be represented. The most common accelerator models are stochastic in nature and involve nonequilibrium plasma properties that are also often poorly understood. Still, nature clearly finds a way to produce simple, robust and almost scale-free energy distributions for the cosmic-rays. Their importance has inspired a number of approaches to examining the production and transport of cosmic-ray particles in numerical simulations. I offer here a brief comparison of some of the methods that have been introduced.