Numerical Simulation of spiral shocks in accretion discs and comparison with observations

吸积盘螺旋激波的数值模拟及与观测结果的比较

基本信息

批准号：
10640231
负责人：
MATSUDA Takuya
金额：
$ 2.05万
依托单位：
KOBE UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2000
项目状态：
已结题

项目摘要

An accretion disc is a gas disc formed around a compact object such as a white dwarf, a neutron star or a black hole. In the present research we performed three-dimensional numerical simulation of an accretion disc in a close binary system. The method employed was a finite volume method called SFS scheme using a Riemann solver. The computational region includes a main star accreting mass and a companion star losing mass. As an equation of state of gas we employed that of the perfect gas. We found that the gas stream (L1 stream) flowing through the L1 point penetrates into the accretion disc in the parameter range considered. We also found that the disc gas rotating about the main star hits the L1 stream and forms an elongated shock. We termed it as the L1 shock. Because of the L1 shock, the disc gas loses its angular momentum and accretes to the main star. We have proposed a mechanism of angular momentum loss by spiral shocks, but its magnitudes may not be large enough to explain observations. The angular momentum loss by the L1 shock was found to be large enough. In 1997 British astronomers discovered spiral structure proposed by us in the cataclysmic variable IP Pegasi. Since then the spiral shock model attracted much attention in the community. The penetration was also discovered recently.One of problems in the above simulation is that radiation cooling was not taken into account explicitly. Instead we reduce the specific ratio from 5/3 to 1.01. In the future research we plan to employ Direct Simulation Monte Carlo method. We already obtained a preliminary result for a two-dimensional case. We plan to extend it to three-dimension, and try to simulate a raditive transfer by solving thermal conduction explicitly.

积聚盘是围绕紧凑型物体形成的气盘，例如白矮人，中子星或黑洞。在本研究中，我们对近二进制系统中的积聚盘进行了三维数值模拟。采用的方法是使用Riemann求解器的有限体积方法称为SFS方案。计算区域包括一个主恒星积聚质量和伴侣恒星失去质量。作为天然气状态的方程式，我们采用了完美的气体。我们发现，在考虑的参数范围内，流过L1点的气流（L1流）渗透到吸积盘中。我们还发现，围绕主恒星旋转的圆盘气撞击L1流并形成细长的冲击。我们将其称为L1冲击。由于L1冲击，圆盘气体失去了其角动量，并吸收了主恒星。我们提出了一种通过螺旋冲击而导致角动量丧失的机制，但其幅度可能不足以解释观察结果。发现L1冲击的角动量损失足够大。 1997年，英国天文学家发现了我们在灾难性变量PEGASI中提出的螺旋结构。从那时起，螺旋冲击模型引起了社区的广泛关注。最近还发现了穿透性。上述模拟中的一个问题是，没有明确考虑辐射冷却。相反，我们将特定比率从5/3降低到1.01。在将来的研究中，我们计划采用直接模拟蒙特卡洛法。我们已经为二维情况获得了初步结果。我们计划将其扩展到三维，并尝试通过明确求解热传导来模拟辐射转移。