From Planetary to Stellar Dynamos - An investigation of the origin and the variability of stellar magnetic fields by direct numerical simulations

从行星到恒星发电机 - 通过直接数值模拟研究恒星磁场的起源和变化

• 批准号: 195528656
• 负责人: Dr. Martin Schrinner
• 金额: --
• 依托单位: Laboratorie de Radioastronomie
• 依托单位国家: 德国
• 项目类别: Research Fellowships
• 财政年份: 2011
• 资助国家: 德国
• 起止时间: 2010-12-31 至 2012-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/195528656?language=en
• 关键词: Planetary; Stellar; Dynamos; investigation; origin

Most low-mass stars possess a magnetic field. Stellar magnetic fields may differ a lot in their field topology, their field strength and their time dependence. Magnetic fields of low-mass stars and planets are maintained by currents resulting from the motion of a conducting fluid (or gas) in their interiors. Thus, the huge variability of stellar magnetic fields is most probably related to differences in the internal structure and interior dynamics of stars. Vice versa, magnetic fields have a major influence on stellar dynamics and stellar evolution in almost all evolutionary states. The proposed work will contribute to an explanation for the origin and the huge variety of stellar magnetic fields. The complexity of the dynamo problem together with a vast range of spatial and temporal scales rendered its direct numerical treatment impossible for long time. Only recently, increasing computer power made global, direct numerical dynamo simulations feasible, in particular for the geodynamo. These models describe the complicated interaction of a convection-driven, conducting and incompressible fluid (liquid iron in the Earth’s outer core) with a magnetic field. However, for stellar dynamos the simplifying assumption of an incompressible fluid is no longer valid, gas is compressible.A recently developed numerical dynamo code takes compressibility into account. We will carry out a systematic parameter study of compressible dynamo simulations guided by well-known results from incompressible modelling. In this way we intend to point out and to explain systematic differences between compressible and incompressible models with respect to the geometry of magnetic fields, the field strength, the time dependence, the mechanism of field generation and the strength and the pattern of differential rotation. A further comparison with observations along these lines will highlight the relevance of compressible effects and will offer insight into the working of stellar dynamos.

大多数低质量恒星都有磁场。恒星磁场可能在其场拓扑、场强度和时间依赖性方面有很大不同。低质量恒星和行星的磁场是由其内部导电流体（或气体）运动产生的电流维持的。因此，恒星磁场的巨大变化很可能与恒星内部结构和内部动力学的差异有关。反之亦然，磁场对几乎所有演化状态的恒星动力学和恒星演化都有重要影响。这项工作将有助于解释恒星磁场的起源和巨大的变化。发电机问题的复杂性，以及广泛的空间和时间尺度，使得它的直接数值处理不可能很长一段时间。直到最近，计算机能力的提高才使全球直接数值发电机模拟成为可能，特别是对地球发电机而言。这些模型描述了对流驱动的、传导的和不可压缩的流体（地球外核的液态铁）与磁场的复杂相互作用。然而，对于恒星发电机，不可压缩流体的简化假设不再成立，气体是可压缩的，最近开发的数值发电机程序考虑了可压缩性。我们将进行一个系统的参数研究的可压缩发电机模拟的指导下，从不可压缩建模的知名结果。这样，我们打算指出和解释系统之间的差异，可压缩和不可压缩模型的几何形状的磁场，磁场强度，时间依赖性，机制的磁场产生和强度和模式的差异旋转。沿着沿着这些路线与观测结果进行进一步的比较，将突出可压缩效应的相关性，并将提供对恒星发电机工作的深入了解。