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1968년 ~ 2025년까지 1,227 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 : 1,227건 (DB Construction : 1,227 Articles)
총 게시글 1,227건
페이지 74/123
731
- BALSARA DINSHAW
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.181-190
- 2001
- 원문 바로보기
The advent of robust, reliable and accurate higher order Godunov schemes for many of the systems of equations of interest in computational astrophysics has made it important to understand how to solve them in multi-scale fashion. This is so because the physics associated with astrophysical phenomena evolves in multi-scale fashion and we wish to arrive at a multi-scale simulational capability to represent the physics. Because astrophysical systems have magnetic fields, multi-scale magnetohydrodynamics (MHD) is of especial interest. In this paper we first discuss general issues in adaptive mesh refinement (AMR), We then focus on the important issues in carrying out divergence-free AMR-MHD and catalogue the progress we have made in that area. We show that AMR methods lend themselves to easy parallelization. We then discuss applications of the RIEMANN framework for AMR-MHD to problems in computational astophysics.
732
- 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.
733
- 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.
734
- IBANEZ JOSE MA.
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.191-201
- 2001
- 원문 바로보기
My contribution to these proceedings summarizes a general overview on High Resolution Shock Capturing methods (HRSC) in the field of relativistic hydrodynamics with special emphasis on Riemann solvers. HRSC techniques achieve highly accurate numerical approximations (formally second order or better) in smooth regions of the flow, and capture the motion of unresolved steep gradients without creating spurious oscillations. In the first part I will show how these techniques have been extended to relativistic hydrodynamics, making it possible to explore some challenging astrophysical scenarios. I will review recent literature concerning the main properties of different special relativistic Riemann solvers, and discuss several 1D and 2D test problems which are commonly used to evaluate the performance of numerical methods in relativistic hydrodynamics. In the second part I will illustrate the use of HRSC methods in several astrophysical applications where special and general relativistic hydrodynamical processes play a crucial role.
735
- PARK BYEONG-GON
- Journal of the Korean astronomical society = 천문학회지
- 34, n.3
- pp.149-155
- 2001
- 원문 바로보기
UBV RI and H<TEX>$\alpha$</TEX> photometry has been performed for the open cluster NGC 6531. A total of 56 bright main sequence (MS) members were selected from their positions in photometric diagrams. We also classified 7 pre-main sequence (PMS) stars and 6 PMS candidates with Ha: emission from H<TEX>$\alpha$</TEX> photometry. We determined a reddening of < E(B - V) >= 0.29 <TEX>$\pm$</TEX> 0.03 and a distance modulus of Vo - Mv = 10.5 for the cluster. From the comparison of our photometric results to theoretical evolution models, we derived a MS turnoff age of 7.5 Myr and a PMS age spread of <TEX>$\~$</TEX>4 Myr. The IMF slope <TEX>$\Gamma$</TEX>, calculated in the mass range of 0.45 <TEX>$\le$</TEX> log m <TEX>$\le$</TEX> 1.35 is a steep value of <TEX>$\Gamma$</TEX> = -1.8 <TEX>$\pm$</TEX> 0.6.
736
- PARK MYEONG-GU
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.305-307
- 2001
- 원문 바로보기
Radiation hydrodynamics in high. velocity or high optical-depth flow should be treated under rigorous relativistic formalism. Relativistic radiation hydrodynamic moment equations are summarized, and its application to the near-critical accretion onto neutron star is discussed. The relativistic effects can dominate the dynamics of the flow even when the gravity is weak and the velocity is small. First order equations fail to describe the intricate relativistic effects correctly.
737
- 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.
738
- MOLTENI D.
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.247-249
- 2001
- 원문 바로보기
The accretion disks are usually supposed symmetric to reflection on the Z=0 plane. Asymmetries in the flow are be ver-y small in the vicinity of the compact accretor. However their existence can have a important role in the case of subkeplerian accretion flows onto black holes. These flows lead to strong heating and even to the formation of shocks close to the centrifugal barrier. Large asymmetries are due to the development of the KH instability triggered by the small turbulences at the layer separating the incoming flow from the out coming shocked flow. The consequence of this phenomenon is the production of asymmetric outflows of matter and quasi periodic oscillations of the inner disk regions up and down the Z=0 plane.
739
- KIM HUN-DAE
- Journal of the Korean astronomical society = 천문학회지
- 34, n.3
- pp.167-179
- 2001
- 원문 바로보기
A molecular line survey towards the UC H II region G34.3+0.15 from 155.3 to 165.3GHz has been conducted with the TRAO 14-m radio telescope. Combined with our previous observations from 84.7 to 115.6GHz and 123.5 to 155.3GHz (Paper I), the spectral coverage of this survey in G34.3+0.15 now runs from 85 to 165 GHz. From these latest observations, a total of 18 lines from 6 species were detected. These include four new lines corresponding to <TEX>${\Delta}$</TEX>J = 0, <TEX>${\Delta}$</TEX>K = 1 transitions of the <TEX>$CH_3OH$</TEX> E-type species, and two new lines corresponding to transitions from <TEX>$SO_2$</TEX> and <TEX>$HC_3N$</TEX>. These 6 new lines are <TEX>$CH_3OH$</TEX>[1(1) - 1(0)E], <TEX>$CH_3OH$</TEX>[2(1) - 2(0)E], <TEX>$CH_3OH$</TEX>[3(1) - 3(0)E], <TEX>$CH_3OH$</TEX>[4(1) - 4(0)E], <TEX>$SO_2$</TEX>[14(1, 13) -14(0, 14)] and <TEX>$HC_3N$</TEX>[18 -17]. We applied a rotation diagram analysis to derive rotation temperatures and column densities from the methanol transitions detected, and combined with NRAO 12-m data from Slysh et al. 1999. Applying a two-component fit, we find a cold component with temperature 13-16K and column density <TEX>$3.3-3.4 {\times} 10^{14} cm^{-2}$</TEX>, and a hot component with temperature 64 - 83K and column density <TEX>$9.3{\times}10^{14} - 9.7 {\times} 10^{14} cm^{-2}$</TEX>. On the other hand, applying just a one-component fit yields temperatures in the 47 -62 K range and column densities from <TEX>$7.5-1.1 {\times} 10^{15} cm^{-2}$</TEX>.
740
- 한수련
- Journal of the Korean astronomical society = 천문학회지
- 34, n.2
- pp.67-80
- 2001
- 원문 바로보기
Chemical evolution of galaxies can be understood by studying the spatial distribution of heavy elements. We selected two nearby galaxies, M31 and M33 and investigated spectrum of their HII regions: a) the elec-tron densities have been derived from the [S II] 6717/6731 ratio along with the most recent atomic constants (Hyung & Aller 1996); b) the electron temperatures were determinated from the Pagel's empirical method. Nebula Model (Hyung 1994) has been employed to predict the spectral line intensities which gives the proper chemical abundances. The model would predict the line intensities correctly only when various input parameters such as the effective central star temperatures, gravity log g, model atmosphere as well as the geometry and the nebula physical condition are appropriate. Thus, the determination of chemical abundances of O, S, N of the two nearby galaxies M31 and M33 has been done, which shows a radial dependance of O/H and N/H: decrease with the distance, or increasing electron temperature due to the elemental deficiency. Abundances of M31 appear to be enhanced than those of M33.