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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 72/122
711
- 김강민
- Journal of the Korean astronomical society = 천문학회지
- 34, n.1
- pp.41-45
- 2001
- 원문 바로보기
We tested the characteristics of the BOAO Medium Dispersion Spectrograph (MDS) such as the CCD capabilities, wavelength shift by gravity direction variation, slit illumination function and efficiency. Then we calculated the appropriate exposure time to obtain the given S/N ratio for several given magnitudes. Also the remaining problems to be improved were discussed.
712
- KIM JONGSOO
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.281-283
- 2001
- 원문 바로보기
As a companion to an adiabatic version developed by Ryu and his coworkers, we have built an isothermal magnetohydrodynamic code for astrophysical flows. It is suited for the dynamical simulations of flows where cooling timescale is much shorter than dynamical timescale, as well as for turbulence and dynamo simulations in which detailed energetics are unimportant. Since a simple isothermal equation of state substitutes the energy conservation equation, the numerical schemes for isothermal flows are simpler (no contact discontinuity) than those for adiabatic flows and the resulting code is faster. Tests for shock tubes and Alfven wave decay have shown that our isothermal code has not only a good shock capturing ability, but also numerical dissipation smaller than its adiabatic analogue. As a real astrophysical application of the code, we have simulated the nonlinear three-dimensional evolution of the Parker instability. A factor of two enhancement in vertical column density has been achieved at most, and the main structures formed are sheet-like and aligned with the mean field direction. We conclude that the Parker instability alone is not a viable formation mechanism of the giant molecular clouds.
713
- 이용삼
- Journal of the Korean astronomical society = 천문학회지
- 34, n.1
- pp.47-57
- 2001
- 원문 바로보기
In this paper we have reconstructed an armillary sphere based on the Method of an Armillary Sphere Making described in the Volume 1 of The Collection of Writings on the Scientific Instruments-Uigijipsol (儀器輯說, two volumes) edited in the 1850's by Nam Byong-Chul (南秉哲, 1817-1863) who was a famous Korean states-man-scientist. Nam achieved convenience and accuracy in the measurements of stellar positions in the manner of selective setting the equatorial, ecliptic and horizontal poles by adding a pole axis exchange ring called Jaigeukkwon (載極圈) between the Three Arrangers of Time and Four Displacements. We made use of 3-dimensional graphic software for modelling Nam's armillary sphere which consisted of five layers-eight rings. Results of simulation showed that the pole axis exchange ring functioned properly in setting the equatorial, ecliptic and horizontal coordinates simply by exchange of positions of specified holes on the ring. We ascertained that the invention of Jaigeukkwon solved inherent problems in the conventional Chinese armillary sphere in computation of real ecliptic coordinates. It was revealed that Nam Byong-Chul made great contributions in the East Asian history of armillary sphere making.
714
- 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.
715
- PARK KYUNG SUN
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.317-319
- 2001
- 원문 바로보기
The response of the earth's magnetosphere to the variation of the solar wind parameters and Interplanetary magnetic field (IMF) has been stud}ed by using a high-resolution, three-dimension magnetohydrodynamic (MHD) simulation when the WIND data of velocity Vx, plasma density, dynamic pressure, By and Bz every 1 minute were used as input. Large electrojet and magnetic storm which occurred on October 21 and 22 are reproduced in the simulation (fig. 1). We have studied the energy transfer and tail reconnect ion in association with geomagnetic storms.
716
- 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.
717
- 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.
718
- 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.
719
- 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.
720
- 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.