Energy flows in stellar coronae

太阳是我们唯一可以详细研究的恒星，从其内部到外层大气(日冕)，以及贯穿整个太阳系的太阳风。日冕也是一个独特的实验室，我们可以用它来了解整个宇宙中发生的基本等离子体过程(其中大部分是由磁化的等离子体组成)。太阳辐照度和粒子通量从根本上影响空间天气、我们的大气和我们星球的全球气候。然而，到目前为止，我们还未能理解关于太阳(以及整个恒星)的许多基本问题。太阳的标准模型最近受到了质疑。我们仍然不知道将日冕加热到数百万度的主要机制，这些机制会导致耀斑和喷发，加速粒子，在极端紫外线(EUV)中产生最强的发射。我们也对极紫外线或X射线中的太阳辐照度及其对地球全球气候的潜在影响知之甚少。至于其他恒星，我们知道大多数都有很强的X射线发射，然而产生这些X射线的过程在很大程度上仍然是未知的。现在是日冕物理学的黄金时代，最近的(SOHO，TRACE，RHESSI)任务收集了大量数据，现在得到了Hinode(Solar-B)的补充，很快又有了STEREO，SDO。两台EUV光谱仪(SOHO/CDS、Hinode/EIS)与英国密切相关。我认为，现在投入更多的资源来分析和解释这些光谱数据是及时的，因为它们掌握着推进我们对日冕的理解的关键。EIS目前的敏感性和分辨率将使新的研究成为可能。特别是，我打算将观测和理论建模结合起来，通过考虑等离子体中的非平衡和非热效应，了解哪些过程主导着日冕中的能量释放和流动。特别是，我将研究日冕环中加热的位置和演变与磁场变化的关系，以及耀斑期间的能量流动与色球蒸发的关系。光谱观测和现实的大气模型也将揭示为什么最亮的EUV线如此明亮的问题，因此在未来，我们也将能够预测它们的排放。我还计划使用独特的长达10年的SOHO观测，首次描述EUV光谱辐照度及其随太阳周期的变化。然后，我们将能够研究对全球气候的任何可能影响。通过同样的观测，我还将获得最后一个周期中日冕的物理特征。有了这些和一些模型，就有可能详细地模拟其他恒星的X射线发射。通过这些模拟，以及钱德拉和XMM-牛顿对不同年龄恒星的观测，将有可能理解在哪些情况下观测到的X射线发射可能是由于类似活跃太阳的热日冕的存在。鉴于准确的原子数据对等离子体诊断和建模的重要性，提供准确的原子数据是这项提议的一个组成部分。我计划继续研究极紫外光和X射线的离子，并提供原子数据，以便研究非平衡和非热效应，这在日冕中可能是重要的。

The Sun is the only star that we can study in detail, from its interior to the outer atmosphere (corona) and the solar wind, which permeates the entire solar system. The solar corona is also an unique laboratory that we can use to understand fundamental plasma processes that occurr throughout the universe (most of which is composed of magnetised plasma). The solar irradiance and particle flux fundamentally affect space weather, our atmosphere and the global climate of our planet. Yet, we have so far failed to understand many fundamental questions about the Sun (and stars in general). The standard model of the Sun has recently been called into question. We still do not know the prime mechanisms that heat the solar corona to millions of degrees, that cause flares and eruptions, that accelerate particles, that produce the strongest emission in the Extreme Ultra Violet (EUV). We also know very little about the solar irradiance in the EUV or X-rays, and its potential effects on the global climate of our planet. As for other stars, we know that most have strong X-ray emission, however the processes that produce these X-rays are still largely unknown. This is a golden age for the physics of the solar corona, with a wealth of data gathered by recent (SOHO, TRACE, RHESSI) missions, now complemented with Hinode (Solar-B), and soon with STEREO, SDO. The two EUV spectrometers (SOHO/CDS, Hinode/EIS) have a strong UK involvement. I believe that it is timely to invest more resources into the analysis and interpretation of these spectroscopic data, because they hold the key to advance our understanding of the solar corona. The current sensitivity and resolution of EIS will allow novel studies. In particular, I intend to couple observations with theoretical modeling to understand which processes dominate the energy release and flow in the corona, by taking into account non-equilibrium and non-thermal effects in the plasma. In particular, I will study the location and evolution of heating in coronal loops in relation with the changes of the magnetic field, and energy flows during flares, in relation to chromospheric evaporation. Spectral observations and realistic atmospheric models will also shed light on the problem of why the brightest EUV lines are so bright, so in the future we will also be able to predict their emission. I also plan to use the unique 10-year long SOHO observations to characterise for the first time the EUV spectral irradiance and its variations with the solar cycle. We will then be able to study any possible effects on global climate. With the same observations I will also obtain the physical characteristics of the solar corona during the last cycle. With these and some modeling, it will be possible to simulate in detail the X-ray emission from other stars. With these simulations, and Chandra and XMM-Newton observations of stars of different ages, it will be possible to understand in which cases the observed X-ray emission could be due to the presence of a hot corona similar to an active Sun. Provision of accurate atomic data forms an integral part of this proposal, given their importance for plasma diagnostic and modeling. I plan to continue the work on the ions for the EUV and X-rays, and to provide atomic data to allow studies of non-equilibrium and non-thermal effects, which are presumably important in the solar corona.