Self-Collimated Jets, Accretion Discs and Young Stars

This paper is focused on the huge dynamical importance of the mass load in magnetized jet models. I will first review some `naive' questions (Why should jets be magnetized? What is the jet driving source?), then show why the jet mass load is so important and why numerical simulations are unable yet to deal with jet formation. I will afterwards briefly describe some results of the only accretion disc model addressing explicitely this question and present a possible star-disc magnetospheric interaction giving rise to time-dependent outbursts.     

Outflows from Dynamo-Active Protostellar Accretion Discs

An axisymmetric model of a cool, dynamo-active accretion disc is applied to protostellar discs. Thermally and magnetically driven outflows develop that are not collimated within 0.1 AU. In the presence of a central magnetic field from the protostar, accretion onto the protostar is highly episodic, which is in agreement with earlier work.     

大质量黑洞吸积盘的径向自引力

本文研究了大质量黑洞吸积盘的自引力,用薄盘位形上积分的方法计算了吸积盘自引力的径向与垂向分量,着重讨论了径向自引力。主要结果为:对于大质量黑洞(M～10~8—10~(10)M_⊙)吸积盘,在(R/R_g)～10~5—10~4的距离上,径向自引力会超过中心天体引力。在这个距离上,吸积盘的动力学结构完全不同于开普勒盘。提出了径向自引力不稳定扰动作为一种能源机制。本文还得到吸积盘自引力与中心天体引力量级比较的两个判据,并由此得到大质量黑洞吸积盘外半径的近似解析估计。本文结果可用于类星体和星系核吸积盘。     

弱磁化等温薄吸积盘的轴对称脉动不稳定性

本文在不考虑粘滞律的条件下，较详细地讨论了弱磁化等温薄吸积盘的轴对称脉动不稳定性．结果表明，对轴对称扰动，盘内存在４种轴对称振荡模式．仅当Ｂｚ和Ｂφ同时存在时磁场才能影响这些振荡模式的不稳定性．Ｂｚ和Ｂφ对其中２种角频率较高的振荡模式（对应于ωＩ）表现为非稳因素，而对其中２种角频率较低的振荡模式（对应于ωＩ）表现为致稳因素．     

磁化吸积盘的不稳定性研究

从磁流体动力学方程组出发,用微扰法得到的色散方程中含有环向磁场.利用全新的反常粘滞和反常阻抗,对吸积盘进行数值计算,结果表明,只有竖直方向的弱磁场才可以引发一种单调不稳定性.磁场对粘性吸积盘表现为非稳定性因素,增长率随磁场的增强而增大,且最大增长率大于理想情况下的值.垂向磁场足够强时,单调不稳定性不会出现.     

Numerical Simulation of Accretion Discs in Close Binary Systems andDiscovery of Spiral Shocks

The history of hydrodynamic numerical simulations for accretion disks in close binary systems is reviewed, in which emphasis is placed, in particular, on the facts that spiral shock waves were numerically found in 1986 by researchers including one of the present authors and that spiral structure was discovered in IP Pegasi in 1997 by Steeghs et al. The results of our two and three-dimensional numerical simulations in recent years are then summarized, with comparison being made with observations. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Radial-Azimuthal Instability of Gas-Pressure-Dominated Accretion Disk with Advection

The radial-azimuthal instability of gas-pressure-dominated accretion disk with advection is examined in this paper. We find that the including of very little advection has significant effects on two acoustic modes, which are no longer complex conjugates of each other. They increase the instability of the O-mode and damp that of the I-mode. We also find that when the azimuthal perturbations are considered, the stability properties of disk are different from that in pure radial perturbation case. The increase of azimuthal wave number will stabilize the acoustic modes but make the viscous mode more unstable and does not change the thermal mode very much for optically thin disk. The I-mode is more stable. The O-mode, viscous mode and thermal mode tend to become more unstable with the increase of azimuthal perturbation wavenumber for optically thick disk. For a geometrically slim, advection-dominated disk, the increasing of azimuthal perturbations make thermal mode more unstable and acoustic mode more stable. This revised version was published online in July 2006 with corrections to the Cover Date.     

黑洞吸积盘的演化及温度分布的热不稳定性

本文在Ｔｈｏｒｎｅ工作的基础上讨论了吸积盘中黑洞的有关参量的演化，以及由Ｓｃｈｗａｒｚｓｃｈｉｌｄ黑洞吸积盘向Ｋｅｒｒ黑洞吸积盘演化过程中对吸积盘辐射通量的影响，最后针对几个典型的辐射过程，分别讨论了黑洞吸积盘在牛顿框架中的温度分布方程与广义相对论的温度分布方程的热不稳定性，并给出此类问题的热不稳定性的判据。     

Magnetorotational instability in stratified, weakly ionized accretion discs

We present a linear analysis of the vertical structure and growth of the magnetorotational instability in stratified, weakly ionized accretion discs, such as protostellar and quiescent dwarf novae systems. The method includes the effects of the magnetic coupling, the conductivity regime of the fluid and the strength of the magnetic field, which is initially vertical. The conductivity is treated as a tensor and is assumed to be constant with height.
We obtained solutions for the structure and growth rate of global unstable modes for different conductivity regimes, strengths of the initial magnetic field and coupling between ionized and neutral components of the fluid. The envelopes of short-wavelength perturbations are determined by the action of competing local growth rates at different heights, driven by the vertical stratification of the disc. Ambipolar diffusion perturbations peak consistently higher above the midplane than modes including Hall conductivity. For weak coupling, perturbations including the Hall effect grow faster and act over a more extended cross-section of the disc than those obtained using the ambipolar diffusion approximation.
Finally, we derived an approximate criterion for when Hall diffusion determines the growth of the magnetorotational instability. This is satisfied over a wide range of radii in protostellar discs, reducing the extent of the magnetic 'dead zone'. Even if the magnetic coupling is weak, significant accretion may occur close to the midplane, rather than in the surface regions of weakly ionized discs.     

Effects of Toroidal Magnetic Fields on the Thermal Instability of Thin Accretion Disks

The standard thin disk model predicts that when the accretion rate is moderately high, the disk is radiation–pressure-dominated and thermally unstable. However, observations indicate the opposite, namely the disk is quite stable. We present an explanation in this work by taking into account the role of the magnetic field which was ignored in the previous analysis.     

含平流双温吸积盘的振荡不稳定性研究

从流体动力学方程出发,用微扰法得出含平流双温吸积盘的径向、环向不稳定性的色散方程．并对平流和径向粘滞力对双温吸积盘的影响进行了较详细的讨论．结果表明：平流和径向粘滞力对声模有较大的影响,且不改变粘滞模和热模的稳定性质．而环向扰动对吸积盘的各种模有着较明显的作用．这一模型有利于解释活动天体的周期和准周期光变现象．     

对等温、有磁薄吸积盘脉动不稳定性的多因素影响

本文从磁流体动力学方程组出发，用微扰法得出等温有磁薄吸积盘径向脉动不稳定性的色散方程，详细讨论了磁场、径向粘滞力和因果性修正的α型粘滞对吸积盘不稳定性的影响．我们的结论是：磁场是一种在全盘区域起作用的非稳因素，它能影响粘滞模式的不稳定性和两种声波模式（O－mode和Ⅰ－mode）的增长率．径向粘滞力是一种在全盘区域起作用的致稳因素，它主要影响两种声波模式的不稳定性．α型粘滞的因果性修正主要在盘内区起作用，它对吸积盘的不稳定性影响较为复杂：对粘滞模式和无磁盘的Ⅰ-mode，它表现为致稳因素，而对O－mode和有磁盘的两种声波模式，则表现为非稳因素．     

Magnetorotational and Tayler Instabilities in the Pulsar Magnetosphere

The magnetospheres around neutron stars should be very particular because of their strong magnetic field and rapid rotation. A study of the pulsar magnetospheres is of crucial importance since it is the key issue to understand how energy outflow to the exterior is produced. In this paper, we discuss magnetohydrodynamic processes in the pulsar magnetosphere. We consider in detail the properties of magnetohydrodynamic waves that can exist in the magnetosphere and their instabilities. These instabilities lead to formation of magnetic structures and can be responsible for short-term variability of the pulsar emission.     

Magnetorotational instability in a rotating liquid metal annulus

Although the magnetorotational instability (MRI) has been widely accepted as a powerful accretion mechanism in magnetized accretion discs, it has not been realized in the laboratory. The possibility of studying MRI in a rotating liquid metal annulus (Couette flow) is explored by local and global stability analysis. Stability diagrams are drawn in dimensionless parameters, and also in terms of the angular velocities at the inner and outer cylinders. It is shown that MRI can be triggered in a moderately rapidly rotating table-top apparatus, using easy-to-handle metals such as gallium. Practical issues of this proposed experiment are discussed.     

Turbulence in Accretion Disks

An accretion disk is an inevitable part of the star forming process. Recent years have witnessed dramatic progress in our understanding of how turbulence arises and transports angular momentum in astrophysical accretion disks. The key conceptual point is that the combination of a subthermal magnetic field and outwardly decreasing differential rotation is subject to the magnetorotational instability. This rapidly generates magnetohydrodynamical (MHD) turbulence, leading to greatly enhanced angular momentum transport. Purely hydrodynamic disks, on the other hand, are stable. Disks that are too cool to couple effectively to the magnetic field will not be turbulent. Fully global three dimensional MHD simulations are now beginning to probe the properties of accretion disks from first principles.     

由束流不稳定性直接放大电磁波的弱磁化修正

本文在文［３］的基础上，考虑背景电磁波色散方程的弱磁化修正，在１＜ωｐｅ／Ωｅ＜１０的范围内（主委适用于太阳高日冕、行星际空间及星系射电喷流等），计算了由束流不稳定性直接放大正常模和反常模的增长率。增长率随着频率、ωｐｅ／Ωｅ、电磁波传播角以及非热电子入射角等参数的变化规律，和忽略磁场时的结果与文［３］大体相同，但是反常模的增长，则随着ωｐｅ／Ωｅ的增大而受到明显的抑制，因而在本文参数范围内，束流不稳定性所放大的电磁波以正常模为主，可以解释太阳ＩＩＩ型爆发和星系射电喷流的偏振性质。     

Accretion, loss, and fractionation of martian water

A recently published model for accretion of water by Mars from asteroids and comets beyond 2.5 AU calls for Mars to have accreted 6-27% of Earth's ocean (equivalent to 600-2700 meters depth on Mars' surface) with a D/H ratio 1.2-1.6 times Standard Mean Ocean Water. This model is shown to provide enough outgassed water to account for the subsequent evolution of D/H because of loss of hydrogen and the D/H ratio in water of hydration found in martian meteoric minerals, but enhanced rate loss of hydrogen from early Mars is necessary to permit adequate fractionation to occur during the lifetime of the planet.