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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 69/119
681
- 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.
682
- 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.
683
- 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.
684
- 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.
685
- 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.
686
- 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.
687
- JONES T. W.
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.225-230
- 2001
- 원문 바로보기
Rarefied cosmic plasmas generally do not achieve thermodynamic equilibria, and a natural consequence of this is the presence of a significant population of charged particles with energies well above those of the bulk population. These are exemplified by the galactic cosmic rays, but the importance of these high energy populations extends well beyond that context. I review here some of the basic issues associated with the propagation and acceleration of cosmic rays, especially in the context of collisionless plasma shocks.
688
- TANUMA SYUNITI
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.309-311
- 2001
- 원문 바로보기
Strong thermal X-ray emission, called Galactic Ridge X-ray Emission, is observed along the Galactic plane (Koyama et al. 1986). The origin of hot (<TEX>$\~$</TEX>7 keV) component of GRXE is not known, while cool (<TEX>$\~$</TEX>0.8 keV) one is associated with supernovae (Kaneda et al. 1997, Sugizaki et al. 2001). We propose a possible mechanism to explain the origin; locally strong magnetic fields of <TEX>$B_{local}\;\~30{\mu}G$</TEX> heat interstellar gas to <TEX>$\~$</TEX>7 keV via magnetic reconnection (Tanuma et al. 1999). There will be the small-scale (< 10 pc) strong magnetic fields, which can be observed as <TEX>$(B)_{obs} \;\~3{\mu}G$</TEX> by integration of Faraday Rotation Measure, if it is localized by a volume filling factor of f <TEX>$\~$</TEX> 0.1. In order to examine this model, we solved three-dimensional (3D) resistive magnetohydrodynamic (MHD) equations numerically to examine the magnetic reconnect ion triggered by a supernova shock (fig.l). We assume that the magnetic field is Bx = 30tanh(y/20pc) <TEX>$\mu$</TEX>G, By = Bz = 0, and the temperature is uniform, at the initial condition. We put a supernova explosion outside the current sheet. The supernova-shock, as a result, triggers the magnetic reconnect ion, and the gas is heatd to > 7 keV. The magnetic reconnect ion heats the interstellar gas to <TEX>$\~$</TEX>7 keV in the Galactic plane, if it occurs in the locally strong magnetic fields of <TEX>$B_{local}\;\~30{\mu}G$</TEX>. The heated plasma is confined by the magnetic field for <TEX>$\~10^{5.5} yr$</TEX>. The required interval of the magnetic reconnect ions (triggered by anything) is <TEX>$\~$</TEX>1 - 10 yr. The magnetic reconnect ion will explain the origin of X-rays from the Galactic ridge, furthermore the Galactic halo, and clusters of galaxies.
689
- ISOBE HIROAKI
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.337-339
- 2001
- 원문 바로보기
One-dimensional hydrodynamic modeling of a protostellar flare loop is presented. The model consists of thermally isolated loop connecting the central core and the accretion disk. We found that the conductive heat flux of a flare heated the accretion disk up to coronal temperature and consequently the disk is evaporated and disappeard. This effect may explain the ovserved feature of the repeated flare from the young stellar object YLW 15.
690
- FUX ROGER
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.255-259
- 2001
- 원문 바로보기
PMDSPH is a combined 3D particle-mesh and SPH code aimed to simulate the self-consistent dynamical evolution of spiral galaxies including live stellar and collisionless dark matter components, as well as an isothermal gas component. This paper describes some aspects of this code and shows how its application to the Milky Way helps to recover the gas flow within the Galactic bar region from the observed HI and CO longitude-velocity distributions.