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.

通过太阳黑子的出现可以在表面看到太阳的磁场，这也与太阳耀斑和日珥有关。太阳黑子的活动并不是恒定的，而是以 11 年为周期出现盛衰。无序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，但周期性行为显示出两个半球之间的相干性，并且显然是整个对流区运行的全局过程。目前尚不清楚磁场如何组织自身以产生如此大规模的周期性行为。太阳的内自转提供了一种自然的大尺度效应，它在对流区底部附近大约三分之二的距离表面上快速变化。我们的工作致力于建立一个周期性活动模型，该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以太阳黑子的形式出现。结合对流效应的简化描述，这个模型将通过数值求解，预计将产生一个具有大尺度特征的自持磁场，可以与太阳行为进行比较。围绕轨道运行的物质盘在许多天文环境中都发现了中心质量，包括年轻恒星周围尘埃气体的原行星盘（行星是在其中形成的）、黑洞周围的高能等离子体吸积盘，以及更熟悉的例子，例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。我们建议研究天体物理圆盘动力学、行星形成物理学和太阳系外行星系统动力学的几个方面。我们将研究圆盘中湍流、磁场和涡流的特性，以及非圆形和扁平圆盘的行为。我们将研究太阳系外行星与其主恒星之间的潮汐相互作用，这种相互作用可以强烈加热甚至摧毁行星，以及行星和圆盘的相互作用，这种相互作用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。太阳物理学的突出问题之一是了解日冕是如何加热的。我们知道，磁场在将能量从太阳表面下方传输到太阳大气中起着关键作用。这种现象发生在从纳耀斑到微耀斑、大耀斑、日珥喷发和日冕物质抛射等多种尺度上。然而，我们尚未完全了解磁能如何转化为热能和动能。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 以及最近的 SDO/AIA）提供了令人惊叹的高空间分辨率图像和高节奏电影。这些表明平衡模型可能不合适，并且可能需要重新审视非平衡效应，例如瞬态电离和复合以及非麦克斯韦电子分布。EUV（和 X 射线）光谱与原子物理计算相结合，正在发挥作用在太阳物理领域发挥着重要作用。它使得等离子体的物理参数（温度和电子密度分布、流量、元素丰度和非热展宽）得以确定，并对各种加热模型施加约束。我们第一次获得了来自 SOHO、Hinode 和 SDO 卫星的足够详细的光谱观测结果，使我们能够直接将观测到的量与理论模型预测的量进行比较，至少对于日冕环和耀斑来说是这样。此外，我们第一次可以将日冕特性与出现时在光球层中观察到的磁场演化联系起来。