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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of The Korean Astronomical Society
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The Korean Astronomical Society
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Volume & Issues
Volume 34, Issue 4 - Dec 2001
Volume 34, Issue 3 - Dec 2001
Volume 34, Issue 2 - Jun 2001
Volume 34, Issue 1 - Apr 2001
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Adaptive Mesh Refinement in Computational Astrophysics - Methods and Applications
BALSARA DINSHAW ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 181~190
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.
Riemann Solvers in Relativistic Hydrodynamics: Basics and Astrophysical Applications
IBANEZ JOSE MA. ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 191~201
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.
Smoothed Particle Hydrodynamics Code Basics
MONAGHAN J. J. ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 203~207
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.
Magnetohydrodynamics Code Basics
RYU DONGSU ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 209~213
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
B = 0, is described. Through tests, the robustness of the upwind schemes for MHDs is demonstrated.
Numerical Method for General Relativistic Magnetohydrodynamics in Kerr Space-Time
KOIDE SHINJI ; SHIBATA KAZUNARI ; KUDOH TAKAHIRO ; MEIER DAVID L. ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 215~224
We present the whole basis of numerical method and useful formulae for general relativistic magnetohydrodynamic simulations in Kerr space-time.
Energetic Nonthermal Particles ('Cosmic-Rays') & Their Acceleration in Collisionless Plasmas
JONES T. W. ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 225~230
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.
Numerical Simulation of Cosmic-Ray Acceleration
JONES T. W. ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 231~235
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.
A Simple Volume Tracking Method For Compressible Two-Phase Flow
SHYUE KEH-MING ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 237~241
Our goal is to present a simple volume-of-fluid type interface-tracking algorithm to compressible two-phase flow in two space dimensions. The algorithm uses a uniform underlying Cartesian grid with some cells cut by the tracked interfaces into two subcells. A volume-moving procedure that consists of two basic steps: (1) the update of volume fractions in each grid cell at the end of the time step, and (2) the reconstruction of interfaces from discrete set of volume fractions, is employed to follow the dynamical behavior of the interface motion. As in the previous work with a surface-tracking procedure for general front tracking (LeVeque & Shyue 1995, 1996), a high resolution finite volume method is then applied on the resulting slightly nonuniform grid to update all the cell values, while the stability of the method is maintained by using a large time step wave propagation approach even in the presence of small cells and the use of a time step with respect to the uniform grid cells. A sample preliminary numerical result for an underwater explosion problem is shown to demonstrate the feasibility of the algorithm for practical problems.
Interaction of Supernova Remnants With the Ambient medium
DWARKADAS VIKRAM V. ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 243~246
We summarize various aspects of the interaction of supernova remnants (SNRs) with the ambient medium. We discuss the evolution' of SNRs in environments sculpted by the progenitor star, and summarize the factors on which this evolution depends. As a specific example, we consider the evolution of the medium around a 35 M
star, and the interaction of the shock wave with this medium when the star explodes as a SN. We also discuss the interaction of Type Ia SNe with the ambient medium, especially the formation and growth of hydrodynamic instabilities.
New Instabilities in Accretion Flows onto Black Holes
MOLTENI D. ; FAUCI F. ; GERARDI G. ; BISIKALO D. ; KUZNETSOV O. ; ACHARYA K. ; CHAKRABARTI S. ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 247~249
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.
Radiation Hydrodynamics of 2-D Accretion Disks
OKUDA TORU ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 251~254
To examine the structure and dynamics of thick accretion disks, we use a two-dimensional viscous hydrodynamic code coupled with radiation transport. The
-model and the full viscous stress-tensor description for the kinematic viscosity are used. The radiation transport is treated in the gray, flux-limited diffusion approximation. The finite difference methods used are based on an explicit-implicit method. We apply the numerical code to the Super-Eddington black-hole model for SS 433.@The result for a very small viscosity parameter a reproduces well the characteristic features of SS 433, such as the relativistic jets with
0.26c, the small collimation degree of the jets, the mass-outflow rate of
, and the formation of the X-ray iron emission lines.
PMDSPH: A Hybrid N-Body and SPH Code and Its Application to the Milky Way
FUX ROGER ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 255~259
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.
SPH Simulations of Barred Galaxies: Evolution of Nuclear Rings
ANN H. B. ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 261~263
Numerical simulations based on the smoothed particle hydrodynamics (SPH) is performed to investigate the dynamical properties of barred galaxies that have nuclear rings. The nuclear ring morphology depends on the relative strength of bar potentials. Nuclear rings form between the two ILRs and align perpendicular to the bars unless the bar potentials are strong enough to allow the x1 orbits near the ILRs. Shock dissipation plays a critical role in the formation of nuclear rings.
Relativistic Hydrodynamics and Quasiperiodic Oscillations
MATHEWS GRANT J. ; FRAGILE P. CHRIS ; WILSON JANES R. ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 265~269
We present preliminary numerical simulations of tilted-disk accretion around a rotating black hole. Our goal is to explore whether hydrodynamic instabilities near the Bardeen-Petterson radius could be responsible for generating moderate-frequency quasi-periodic oscillations in X-ray binaries. We review the relevant general relativistic hydrodynamic equations, and discuss preliminary results on the structure and dynamics of a thin, Keplerian disk.
Superconservative Finite Difference Scheme for Gas Dynamics
KOVALENKO ILYA G. ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 271~273
We present a 4-parameter implicit Lagrangean code which satisfies conservation of mass, linear and angular momenta, energy and entropy simultaneously. The primary advantage of this scheme is possibility to control dissipative properties of the scheme avoiding the effects of numerical viscosity.
Simulations on Incompressible MHD Turbulence
CHO JUNGYEON ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 275~279
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.
An Isothermal Mganetohydrodynamic Code and Its Application to the Parker Instability
KIM JONGSOO ; RYU DONGSU ; JONES T. W. ; HONG S. S. ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 281~283
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.
Three-Dimensional Simulations of the Jeans-Parker Instability
LEE SANG MIN ; HONG SEUNG SOO ; KIM AND JONGSOO ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 285~287
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.
Hydrodynamic approach to cosmic ray acceleration
KO CHUNG-MING ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 289~291
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.
Diffusive Shock Acceleration with Self-Consistent Injection
KANG HYESUNG ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 293~295
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
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.
Structure and Physical Conditions in MHD Jets from Young Stars
SHANG HSIEN ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 297~299
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.
Electric Charge and Magnetic Flux on Astrophysical Black Hole
LEE HYUN KYU ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 301~303
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
BJ with a horizon flux of
, 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.
Relativistic Radiation Hydrodynamics of Spherical Accretion
PARK MYEONG-GU ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 305~307
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.
Three-Dimensional Numerical Magnetohydrodynamic Simulations of Magnetic Reconnection in the Interstellar Medium
TANUMA SYUNITI ; YOKOYAMA TAKAAKI ; KUDOH TAKAHIRO ; SHIBATA KAZUNARI ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 309~311
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 (
7 keV) component of GRXE is not known, while cool (
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
heat interstellar gas to
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
by integration of Faraday Rotation Measure, if it is localized by a volume filling factor of f
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)
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
7 keV in the Galactic plane, if it occurs in the locally strong magnetic fields of
. The heated plasma is confined by the magnetic field for
. The required interval of the magnetic reconnect ions (triggered by anything) is
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.
Spiral Waves and Shocks in Discs around Black Holes: Low Compressibility and High Compressibility Models
LANZAFAME GIUSEPPE ; BELVEDERE GAETANO ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 313~315
Some authors have concluded that spiral structures and shocks do not develop if an adiabatic index
> 1.16 is adopted in accretion disc modelling, whilst others have claimed that they obtained well defined spirals and shocks adopting a
= 1.2 and a
= 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
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.
Global MHD Simulation of the Earth's Magnetosphere Event on October, 1999
PARK KYUNG SUN ; OGINO TATSUKI ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 317~319
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.
Transonic Magnetohydrodynamic Turbulence
LEE HYESOOK ; RYU DONGSU ; KIM JONGSOO ; JONES T. W. ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 321~323
Compressible, magnetohydrodynamic (MHD) turbulence in two dimension is studied through high-resolution, numerical simulations with the isothermal equation of state. First, hydrodynamic turbulence with Mach number
1 is generated by enforcing a random force. Next, initial, uniform magnetic field of various strengths with Alfvenic Mach number Ma
1 is added. Then, the simulations are followed until MHD turbulence is fully developed. Such turbulence is expected to exist in a variety of astrophysical environments including clusters of galaxies. Although no dissipation is included explicitly in our simulations, truncation errors produce dissipation which induces numerical resistivity. It mimics a hyper-resistivity in our second-order accurate code. After saturation, the resulting flows are categorized as SF (strong field), WF (weak field), and VWF (very weak field) classes respectively, depending on the average magnetic field strength described with Alfvenic Mach number,
. The characteristics of each class are discussed.
Collapse of Magnetised, Singular Isothermal Toroids
ALLEN ANTHONY ; SHU FRANK ; LI ZHI- YUN ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 325~327
This poster summarizes numerical collapse calculations of non-rotating and rotating singular, isothermal toroids that employed the zeus2d (Norman and Stone 1992) magnetohydrodynamics package. In the non-rotating collapse calculations, it is seen that infall proceeds at a constant rate and magnetically supported, high density pseudo-disks form in the equatorial plane. With rotating clouds, however, toroidal magnetic fields grow as infall proceeds, teaming with angular momentum to slow the inflow to the center and generate outflow.
Numerical Study of AGN Jet Propagation with Two Dimensional Relativistic Hydrodynamic Code
MIZUTA AKIRA ; YAMADA SHOICHI ; TAKABE HIDEAKI ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 329~331
We investigate the morphology of Active Galactic Nuclei(AGN) jets. AGN jets propagate over kpc
Mpc and their beam velocities are close to the speed of light. The reason why many jets propagate over so long a distance and sustain a very collimated structure is not well understood. It is argued that some dimensionless parameters, the density and the pressure ratio of the jet beam and the ambient gas, the Mach number of the beam, and relative speed of the beam compared to the speed of light, are very useful to understand the morphology of jets namely, bow shocks, cocoons, nodes etc. The role of each parameters has been studied by numerical simulations. But more research is necessary to understand it systematically. We have developed 2D relativistic hydrodynamic code to analyze relativistic jets. We pay attention to the propagation velocity which is derived from 1D momentum balance in the frame of the working surface. We show some of our models and discuss the dependence of the morphology of jets on the parameter.
Turbulence Driven by Supernova Explosions in a Radiatively-Cooling Magnetized Interstellar Medium
KIM JONGSOO ; BALSARA DINSHAW ; MAC LOW MORDECAI-MARK ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 333~335
We study the properties of supernova (SN) driven interstellar turbulence with a numerical magnetohydrodynamic (MHD) model. Calculations were done using the RIEMANN framework for MHD, which is highly suited for astrophysical flows because it tracks shocks using a Riemann solver and ensures pressure positivity and a divergence-free magnetic field. We start our simulations with a uniform density threaded by a uniform magnetic field. A simplified radiative cooling curve and a constant heating rate are also included. In this radiatively-cooling magnetized medium, we explode SNe one at a time at randomly chosen positions with SN explosion rates equal to and 12 times higher than the Galactic value. The evolution of the system is basically determined by the input energy of SN explosions and the output energy of radiative cooling. We follow the simulations to the point where the total energy of the system, as well as thermal, kinetic, and magnetic energy individually, has reached a quasi-stationary value. From the numerical experiments, we find that: i) both thermal and dynamical processes are important in determining the phases of the interstellar medium, and ii) the power index n of the
relation is consistent with observed values.
Numerical Simulation of a Protostar Flare Loop between the Core and Disk
ISOBE HIROAKI ; YOKOYAMA TAKAAKI ; SHIBATA KAZUNARI ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 337~339
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.
Origin of the Cometary Structure of the HVCs: 3D-MHD Numerical Simulations
SANTILLAN ALFREDO ; FRANCO JOSE ; KIM JONGSOO ;
Journal of The Korean Astronomical Society, volume 34, issue 4, 2001, Pages 341~343
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