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Solar, stellar and planetary astrophysics in DAMTP

DAMTP 中的太阳、恒星和行星天体物理学

基本信息

批准号：
ST/J001570/1
负责人：
Gordon Ogilvie
金额：
$ 78.38万
依托单位：
University of Cambridge
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2012
资助国家：
英国
起止时间：
2012 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=ST%2FJ001570%2F1
关键词：
Solar stellar planetary astrophysics DAMTP

项目摘要

The Sun's magnetic field can be seen at the surface through the appearance of sunspots, which are also associated with solar flares and prominences. Sunspot activity is not constant, but waxes and wanes on an 11-year timescale. Disordered magnetic fields can be maintained by the turbulent motions of the plasma making up the outer part of the Sun, but the cyclical behaviour shows coherence between the two hemispheres and is clearly a global process operating throughout this convective zone. It is not clearly understood how the magnetic field organizes itself to produce such large-scale cyclical behaviour. A natural large-scale effect is provided by the internal rotation of the Sun, which varies rapidly near the base of the convection zone about two-thirds of the distance to the surface. Our work is devoted to producing a model of cyclical activity that draws its energy from this shearing motion and produces the rising magnetic field structures that eventually emerge as sunspots through the mechanism of magnetic buoyancy. Together with a simplified description of the effect of the convection, this model, which will be solved numerically, is expected to lead to a self-sustaining magnetic field with large-scale features that can be compared with solar behaviour.Discs of matter orbiting around a central mass are found in numerous astronomical settings, including protoplanetary discs of dusty gas surrounding young stars, where planets are formed, high-energy plasma accretion discs around black holes, and more familiar examples such as Saturn's rings and spiral galaxies. A great variety of planets and planetary systems continue to be discovered around other stars. We propose to investigate several aspects of the dynamics of astrophysical discs, the physics of planet formation and the dynamics of extrasolar planetary systems. We will study the properties of turbulence, magnetic fields and vortices in discs, and the behaviour of discs that are not circular and flat. We will investigate the tidal interaction between extrasolar planets and their host stars, which can strongly heat or even destroy the planets, and the interaction of planets and discs, which can greatly modify the size and shape of the planets' orbits. All this work is related to current observations.One of the outstanding problems in solar physics is to understand how the solar corona is heated. We know that the magnetic field plays a key role in transporting and transferring energy from beneath the solar surface into the solar atmosphere. This happens on many scales from nanoflares to microflares, major flares, prominence eruptions and coronal mass ejections. However, we do not yet fully understand how magnetic energy is converted into thermal and kinetic energy. Recent observations show that the solar atmosphere is highly dynamic; imaging instruments (SoHO/EIT, TRACE, Stereo, Hinode/XRT and more recently SDO/AIA) have provided spectacular high-spatial-resolution images and high-cadence movies. These suggest that equilibrium models may not be appropriate and non-equilibrium effects may need to be revisited, for example transient ionization and recombination and non-Maxwellian electron distributions.EUV (and X-ray) spectroscopy, combined with atomic physics calculations, is playing a major role in the field of solar physics. It is enabling the physical parameters of the plasma (temperature and electron density distributions, flows, elemental abundances and non-thermal broadening) to be determined and constraints to be placed on the various heating models. For the first time, we have spectroscopic observations from the SOHO, Hinode and SDO satellites detailed enough that we can directly compare observable quantities with those predicted by theoretical modelling, at least for coronal loops and flares. Also, for the first time, we can link the coronal properties with the evolution of the magnetic field as is observed in the photosphere while emerging.

太阳的磁场可以通过太阳黑子的出现在表面看到，太阳黑子也与太阳耀斑和太阳黑子有关。太阳黑子的活动并不是恒定不变的，而是在11年的时间尺度上盛衰交替。混乱的磁场可以通过构成太阳外部的等离子体的湍流运动来维持，但周期性行为显示了两个半球之间的一致性，并且显然是贯穿这个对流区的全球过程。人们还不清楚磁场是如何组织自己产生如此大规模的周期性行为的。太阳的内部自转提供了一种自然的大尺度效应，它在对流区底部附近快速变化，大约是到表面距离的三分之二。我们的工作致力于建立一个周期性活动的模型，从这种剪切运动中汲取能量，并产生上升的磁场结构，最终通过磁浮力机制形成太阳黑子。结合对流效应的简化描述，这一模型将通过数值求解，预计将导致一个具有大尺度特征的自持磁场，可以与太阳的行为进行比较。在许多天文环境中发现了围绕中心质量运行的物质盘，包括围绕年轻恒星的尘埃气体的原行星盘，行星在那里形成，黑洞周围的高能等离子体吸积盘，以及更熟悉的例子，如土星环和螺旋星系。在其他恒星周围不断发现各种各样的行星和行星系统。我们打算研究天体物理盘的动力学、行星形成的物理学和太阳系外行星系统的动力学等几个方面。我们将研究圆盘中的湍流、磁场和涡流的性质，以及非圆形和扁平圆盘的行为。我们将研究太阳系外行星和它们的宿主恒星之间的潮汐相互作用，这可以强烈加热甚至摧毁行星，以及行星和圆盘之间的相互作用，这可以极大地改变行星轨道的大小和形状。所有这些工作都与当前的观测有关。太阳物理学中的一个突出问题是了解日冕是如何被加热的。我们知道，磁场在将能量从太阳表面下输送和转移到太阳大气层中起着关键作用。这发生在许多尺度上，从纳米耀斑到微耀斑，大耀斑，日珥爆发和日冕物质抛射。然而，我们还没有完全理解磁能是如何转化为热能和动能的。最近的观测表明，太阳大气层是高度动态的;成像仪器（SoHO/EIT、TRACE、Stereo、Hinode/XRT和最近的SDO/AIA）提供了壮观的高空间分辨率图像和高节奏电影。这表明平衡模型可能并不合适，可能需要重新考虑非平衡效应，例如瞬时电离和复合以及非麦克斯韦电子分布，极紫外（和X射线）光谱与原子物理计算相结合，在太阳物理学领域发挥着重要作用。它使得能够确定等离子体的物理参数（温度和电子密度分布、流动、元素丰度和非热加宽），并对各种加热模型施加约束。这是第一次，我们有足够详细的SOHO，Hinode和SDO卫星的光谱观测，我们可以直接将可观测的数量与理论模型预测的数量进行比较，至少对于日冕环和耀斑。此外，我们第一次可以将日冕的性质与磁场的演化联系起来，就像在光球层中观察到的那样。