Modeling the three-dimensional structure and dynamics of the corona of the Sun and stars

像我们的太阳这样一颗很酷的恒星周围有一个外层大气，即日冕，它比它的表面温度高一百倍，仍然是一个未解之谜。在其他加热过程中，有人认为日冕中的磁力线是通过恒星表面的运动编织而成的。随后感应电流的消散导致电晕的有效加热高达一百万度。随着计算机技术的进步，我们现在可以通过包括磁场在内的流体动力学的三维随时间变化的模型来研究日冕。我们的模拟结合了极端紫外线发射线光谱的合成，这是与观测进行详细比较所必需的。这些模型将首次解释强磁场和弱磁场区域之间的复杂相互作用，从而能够研究低日冕的3D结构和动力学。如果我们的初步结果得到证实，我们可以提供充分的证据，证明场线编织确实是主要的加热机制，这将是理解日冕加热的一大步。我们的结果也将对其他天体中的热磁加热等离子体的研究产生影响，比如围绕着一颗新形成的恒星及其(潜在)行星的吸积盘。此外，日冕作为极端紫外线辐射的来源，对地球上S大气的化学也很有意义。

A cool star like our Sun is surrounded by an outer atmosphere, the corona, which is a hundred times hotter than its surface ¿ still being an unsolved puzzle. Among other heating processes it was suggested that the magnetic field lines in the corona are braided by motions on the stellar surface. The subsequent dissipation of the induced currents leads to efficient heating of the corona up to a million degrees. The progress in computer power now allows us to study the corona by means of three-dimensional time-dependent models of the fluid dynamics including magnetic fields. Our simulations are coupled with a synthesis of extreme ultraviolet emission line spectra, which is essential for a detailed comparison to observations. These models will be the first to account for the complex interaction of regions with strong and weak magnetic fields, allowing for an investigation of the 3D structure and dynamics of the low corona. If our preliminary results will be substantiated, we can provide ample evidence that the field line braiding indeed is the dominant heating mechanism, which would be a large step forward in understanding coronal heating. Our results will also have impact on the study of hot magnetically heated plasmas in other astrophysical objects, like accretion disks surrounding a newly formed star with its (potential) planets. Furthermore, the solar corona as being the source of the extreme ultraviolet radiation, is of interest for the chemistry of the upper Earth s atmosphere.