모달창 닫기
- 홈으로 이동
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 71/122
701
- SANTILLAN ALFREDO
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.341-343
- 2001
- 원문 바로보기
Here were continue the MHD study started by Santillan et al (1999) for the interaction of high-velocity clouds (HVCs) with the magnetized thick gaseous disk of our Galaxy. We use the MHD code ZEUS-3D and perform 3D-numerical simulations of this interaction, and study the formation of head-tail structures in HVCs. Our results show that clouds located above 2 kpc from mindplane present velocity and column density gradients with a cometary structure that is similar to those observed in 21 cm emission
702
- LANZAFAME GIUSEPPE
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.313-315
- 2001
- 원문 바로보기
Some authors have concluded that spiral structures and shocks do not develop if an adiabatic index <TEX>$\gamma$</TEX> > 1.16 is adopted in accretion disc modelling, whilst others have claimed that they obtained well defined spirals and shocks adopting a <TEX>$\gamma$</TEX> = 1.2 and a <TEX>$M_2/ M_1$</TEX> = 1 stellar mass ratio. In our opinion, it should be possible to develop spiral structures for low compressibility gas accretion discs if the primary component is a black hole. We considered a primary black hole of 8M0 and a small secondary component of 0.5M<TEX>$\bigodot$</TEX> to favour spiral structures formations and possible spiral shocks via gas compression due to a strong gravitational attraction. We performed two 3D SPH simulations and two 2D SPH simulations and characterized a low compressibility model and a high compressibility model for each couple of simulations. 2D models reveal spiral structures existence. Moreover, spiral shocks are also evident in high compressibility 2D model at the outer disc edge. We believe that we could develop even well defined spiral shocks considering a more massive primary component.
703
- SHANG HSIEN
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.297-299
- 2001
- 원문 바로보기
We have constructed the foundations to a series of theoretical diagnostic methods to probe the jet phenomenon in young stars as observed at various optical forbidden lines. We calculate and model in a self-consistent manner the physical and radiative processes which arise within an inner disk-wind driven magneto centrifugally from the circumstellar accretion disk of a young sun-like star. Comparing with real data taken at high angular resolution, our approach will provide the basis of systematic diagnostics for jets and their related young stellar objects, to attest the emission mechanisms of such phenomena. This work can help bring first-principle theoretical predictions to confront actual multi-wavelength observations, and will bridge the link between many very sophiscated numerical simulations and observational data. Analysis methods discussed here are immediately applicable to new high-resolution data obtained with HST and Adaptic Optics.
704
- KO CHUNG-MING
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.289-291
- 2001
- 원문 바로보기
To study the structure and dynamics of a cosmic-ray-plasma system, hydrodynamic approach is a fairly good approximation. In this approach, there are three basic energy transfer mechanisms: work done by the plasma flow against pressure gradients, cosmic ray streaming instability and stochastic acceleration. The interplay between these mechanisms gives a range of structures. We present some results of different version of the hydrodynamic approach, e.g., flow structure, injection, instability, acceleration with and without shocks.
705
- LEE SANG MIN
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.285-287
- 2001
- 원문 바로보기
We have studied the nonlinear evolution of a magnetized disk of isothermal gas, which is sustained by its self-gravity. Our objective is to investigate how the Jeans, Parker, and convective instabilities compete with each other in structuring/de-structuring large scale condensations in such disk. The Poisson equation for the self-gravity has been solved with a fourth-order accurate Fourier method along with the Green function, and the MHD part has been handled by an isothermal TVD code. When large wavelength perturbations are applied, the combined action of the Jeans and Parker instabilities suppresses the development of the convection and forms a dense core of prolate shape in the mid-plane. Peripheral structures around it are filamentary. The low density filaments connect the dense core to the diffuse upper region. On the other hand, when small wavelength perturbations are applied, the disk develops into an equilibrium state which is reminiscent of the Mouschovias's 2-D non-linear equilibrium of the classical Parker instability under an externally given gravity.
706
- LEE C.-W.
- Journal of the Korean astronomical society = 천문학회지
- 34, n.2
- pp.111-117
- 2001
- 원문 바로보기
Recently, we have set up a new digital CCD camera system, MicroMax YHS-1300 manufactured by Roper Scientific for Ha observation by Solar Flare Telescope at Bohyunsan Optical Astronomy Observatory. It has a 12 bit dynamic range, a pixel number of 1300<TEX>$\times$</TEX>1030, a thermoelectric cooler, and an electric shutter. Its readout speed is about 3 frames per second and the dark current is about 0.05 e-/p/s at <TEX>$-10^{\circ}C$</TEX>. We have made a system performance test by confirming the system linearity, system gain, and system noise that its specification requires. We have also developed a data acquisition software which connects a digital camera con-troller to a PC and acquires H<TEX>$\alpha$</TEX> images via Microsoft Visual C++ 6.0 under Windows 98. Comparisons of high quality H<TEX>$\alpha$</TEX> images of AR 9169 and AR 9283 obtained from SOFT with the corresponding images from Learmonth Solar Observatory in Australia confirm that our H<TEX>$\alpha$</TEX> digital observational system is performed properly. Finally, we present a set of H<TEX>$\alpha$</TEX> images taken from a two ribbon flare occurred in AR 9283.
707
- LEE YOUNGUNG
- Journal of the Korean astronomical society = 천문학회지
- 34, n.1
- pp.1-8
- 2001
- 원문 바로보기
We present a fast reduction method of survey data obtained using a single-dish radio telescope. Along with a brief review of classical method, a new method of identification and elimination of negative and positive bad channels are introduced using cloud identification code and several IRAF (Image Reduction and Analysis Facility) tasks relating statistics. Removing of several ripple patterns using Fourier Transform is also discussed. It is found that BACKGROUND task within IRAF is very efficient for fitting and subtraction of base-line with varying functions. Cloud identification method along with the possibility of its application for analysis of cloud structure is described, and future data reduction method is discussed.
708
- MONAGHAN J. J.
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.203-207
- 2001
- 원문 바로보기
SPH is the shorthand for Smoothed Particle Hydrodynamics. This method is a Lagrangian method which means that it involves following the motion of elements of fluid. These elements have the characteristics of particles and the method is called a particle method. A useful review of SPH (Monaghan 1992) gives the basic technique and how it can be applied to numerous problems relevant to astrophysics. You can get some basic SPH programs from http) /www.maths.monash.edu.au/jjm/sphlect In the present lecture I will assume that the student has studied this review and therefore understands the basic principles. In today's lecture I plan to approach the equations from a different perspective by using a variational principle.
709
- SOHN YOUNG-JONG
- Journal of the Korean astronomical society = 천문학회지
- 34, n.2
- pp.59-66
- 2001
- 원문 바로보기
In this paper, we investigate the correlation between the radial ultraviolet color distribution and the shapes of the ultraviolet isophote for elliptical galaxies (M32, NGC 1399) and spiral bulges (of M31, M81) by using their archival UIT images. For M31, M81, and NGC 1399, the radial ultraviolet color distributions show a two-component trend; as the distance from the galactic center increase the color becomes redder in the inner region while it becomes bluer in the outer region. On the other hand, the color of M32 continues to become bluer with the increasing galactocentric distance. We also find, unlike the optical/IR images, significant variations of the position angle and the ellipticity in the ultraviolet isophotes of M31, M81, and NGC 1399 through the inner regions. For M32, the variation is significant in the outer region. Since these variation implies the triaxiality of their intrinsic shapes, we suggest that the early-type galaxies and spiral bulges with a radial color gradient in ultraviolet tend to have a triaxiality. On the other hand, the shape parameter characterized by the fourth order cosine Fourier coefficient of the isophote, a(4)/a, indicates that the systematic deviations of the ultraviolet isophotes of the four galaxies are smaller than <TEX>$\~0.2\%$</TEX> in units of the semi-major axis. The latter result implies that the ultraviolet isophotes of the galaxies have a pure elliptical shape rather than the boxy or disky shapes. Therefore, there is no clear evidence of correlation between the radial ultra-violet color gradient and the boxy/disky shapes of isophotes.
710
- RYU DONGSU
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.209-213
- 2001
- 원문 바로보기
This paper describes the numerical solution to the hyperbolic system of magnetohydrodynamic (MHD) equations. First, by pointing out the approximations involved, the deal MHD equations are presented. Next, the MHD waves as well as the associated shocks and discontinuities, are presented. Then, based on the hyperbolicity of the ideal MHD equations, the application of upwind schemes, which have been developed for hydrodynamics, is discussed to solve the equations numerically. As an definite example, one and multi-dimensional codes based on the Total Variation Diminishing scheme are presented. The treatment in the multi-dimensional code, which maintains <TEX>${\nabla}{\cdot}$</TEX>B = 0, is described. Through tests, the robustness of the upwind schemes for MHDs is demonstrated.