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双星中磁场存在与非同步转动的研究
其他题名The Study of Asynchronous Rotation and Existence of Magnetic Fields in Binary Systems
张瑞玉
学位类型硕士
导师李焱
2012-05
学位授予单位中国科学院研究生院(云南天文台)
学位授予地点北京
学位专业天体物理
关键词双星 磁场 同步转动
摘要在双星的演化中有很多物理过程,其中一部分物理过程对双星自转与公转的同步或非同步状态有影响。如果自行处于潮汐锁定状态,子星的内部在潮汐作用下,转动速度也与公转完全一致,成为刚性转动。 因此,只有在双星子星的自转与公转非同步转动的情况下,子星内部才会存在较差转动.根据磁场产生的Tayler-Spruit发电机原理,较差转动是恒星产生磁场的原因. 即磁场必然存在于非同步转动的双星系统. 我们使用了一种新的方法,考虑了双星间的潮汐作用和演化中进行的其他物理过程,包括物质交换, 星风, 演化中的体积变化, 以及外拉格朗日点物质丢失等. 能够准确计算演化中双星自转和公转的角速, 进而得到双星系统是否处于同步转动状态。.数值计算结果表明,密近双星系统在主序演化时,潮汐摩擦会在较短的时间内使自转与公转达到比较接近的状态, 此后经过一个较长时间的维持在接近同步转动的状态, 星风以及演化中的体积变化不足以导致非同步转动. 对于半相接的双星系统,物质交换可以造成明显的非同步效应,子星内部存在产生磁场的条件. 主星充满洛希瓣之后自转与公转偏离较小,次星偏离较大,次星内部可能存在着比主星强得多的磁场. 对相接双星来说,由于两颗星距离太近潮汐作用远远大于物质交换,自转与公转一直接近于完全同步的状态。本文同时比较了非同步双星模型与同步双星模型演化曲线在赫罗图上的不同, 结果表明非同步模型在物质交换阶段主星演化曲线向赫罗图光度和有效温度高的方向移动。最后将数值计算结果与观测数据进行对比后发现,该模型可以很好的解释观测上双星超过潮汐锁定时标后仍然存在非同步转动的现象。
其他摘要There are a lot of physical processes in the binary systems during the evolution. Many processes have influence on the rotation of the components toward synchronization or non-synchronization. In the case of synchronous rotation, the interior of the components rotates rigidly. It exists, hence, differential rotation in the components only during the asynchronous rotation of the systems. According to the Tayler-Spruit dynamo, the generation of magnetic fields in stars are due to the existence of differential rotation. Therefore, the existence of magnetic fields in binary systems is closely related to the asynchronous rotation. A method considering the actions of many physical processes simultaneously is proposed here to calculate the spin and orbital periods in binary systems, which include mass exchange, stellar wind and mass overflow from outer Lagrangian point. By this method we can get whether the binary is in synchronization during evolution.The results of detailed computations with this method indicate that the spin and orbitperiods can be reached near synchronization in a short time, but it takes long time to reach completely synchronization if the system have reached synchronous rotation, stellar wind and volume change cased by evolution have little influence on synchronization during main sequence. As mass exchange started, the synchronization rotation can be changed into non-synchronization rotation for semi-detached binaries. There exist, therefore, differential rotations and magnetic fields in the components. However, the degree of asynchronous is different for the primary and secondary. It means that the strength of differential rotation and magnetic field may be different in both of the components. For contact binary systems, tidal effect are so strong that mass exchange can not case obvious asynchronous rotation. The evolution tracks in HR diagram of synchronization and non-synchronization are also compared with each other, the result show that the model considers non-synchronization moves to high luminosity and high temperature during mass exchange stage. Finally, the result is compared with observational date and the non-synchronization after tidal-lock timescale in binaries can be explained by this model.
学科领域天文学
语种中文
文献类型学位论文
条目标识符http://ir.ynao.ac.cn/handle/114a53/5334
专题恒星物理研究组
推荐引用方式
GB/T 7714
张瑞玉. 双星中磁场存在与非同步转动的研究[D]. 北京. 中国科学院研究生院(云南天文台),2012.
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