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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 70/122
691
- 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.
692
- 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.
693
- 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.
694
- 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.
695
- 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.
696
- 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.
697
- 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.
698
- 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.
699
- 심경진
- Journal of the Korean astronomical society = 천문학회지
- 34, n.2
- pp.119-127
- 2001
- 원문 바로보기
We have analyzed 210 data of daily sunspot observations made during the period of January 3 to December 31 in 2000 and presented the daily relative sunspot numbers. For this work we estimated the conversion factors to derive the relative sunspot numbers: k=0.72 for the 20 cm refractor and k=0.56 for Solar Flare Telescope in KAO. During the year of 2000, our annual average of relative sunspot numbers is found to be 99.4. This number is obtained from the averaged daily number of 8.9 spot groups, in which there are about 62.5 distinct spots observed. According to the appearance of 423 spot groups, our analysis shows that the mean life time of the spot groups is about 4 day and 12.0 hours.
700
- CHO JUNGYEON
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.275-279
- 2001
- 원문 바로보기
The study of incompressible magnetohydrodynamic (MHD) turbulence gives useful insights on many astrophysical problems. We describe a pseudo-spectral MHD code suitable for the study of incompressible turbulence. We review our recent' works on direct three-dimensional numerical simulations for MHD turbulence in a periodic box. In those works, we use a pseudo-spectral code to solve the incompressible MHD equations. We first discuss the structure and properties of turbulence as functions of scale. The results are consistent with the scaling law recently proposed by Goldreich & Sridhar. The scaling law is based on the concept of scale-dependent isotropy: smaller eddies are more elongated than larger ones along magnetic field lines. This scaling law substantially changes our views on MHD turbulence. For example, as noted by Lazarian & Vishniac, the scaling law can provide a fast reconnection rate. We further discuss how the study of incompressible MHD turbulence can help us to understand physical processes in interstellar medium (ISM) by considering imbalanced cascade and viscous damped turbulence.