A HIGH-RESOLUTION IMAGING SPECTROMETER FOR VISIBLE CORONAL EMISSION LINES

地球通过从太阳流出的磁化等离子体的海洋运行，这被称为太阳风。日冕物质抛射(CME)在太阳风中高速传播，是与太阳喷发和耀斑相关的巨大高密度等离子体云。地球磁场起到了屏蔽的作用，防止日冕物质抛射造成的损害。然而，社会对卫星的依赖和大型CME在一定条件下可能造成广泛的破坏。预测日冕物质抛射的发生及其后续演变的能力，关键取决于对日冕中发生的主要物理过程的了解，以及对日冕物质抛射传播媒介--太阳风的了解。在理解太阳风和日冕物质抛射的过程中，扩展的内冕是一个关键区域。这个复杂的区域从太阳表面开始，延伸到日冕等离子体开始径向膨胀并变得超音速的地方。目前对这一区域的观测非常有限。有一些宽带可见光日冕仪提供了来自日冕电子的汤姆森散射光的相当嘈杂的测量结果，例如COR1/STEREO日冕仪或MLSO MKIV日冕仪(即将升级为COSMO)。目前的极紫外成像仪和光谱仪提供了非常高质量的数据，但它们的视场通常最多只有光球层太阳半径的十分之几。目前还没有使用中的光谱仪可以从日冕边缘观测到日冕半径的十分之几，这严重限制了理解日冕物质抛射和太阳风来源区域的努力。拟议的光谱仪的目标是利用日冕禁止发射线在可见光和近红外中的诊断特性，推断电子温度、离子密度、元素丰度和电荷态、整体流动速度、非热加热(即波加热)以及间接的日冕磁场特性。观测这些谱线的科学优势主要来自于它们的辐射激发成分的强度，这使得发射能够延伸到大的日心距离。因此，令人惊讶的是，在当前的太阳飞行任务中，对可见光中被禁止的日冕发射线的观测被严重忽视。拟议中的光谱仪直接解决了这一缺点，并将对将太阳大气加热到超过100万度并加速太阳风的物理过程提供独特的约束。

The Earth orbits through a sea of magnetised plasma flowing from the Sun called the solar wind. Travelling at high speed through the solar wind, Coronal Mass Ejections (CME) are enormous clouds of high-density plasma associated with eruptions and flares at the Sun. The Earth's magnetic field acts as a shield to prevent damage from CMEs. Society, however, depends on satellites and large CMEs under certain conditions may cause widespread damage. The ability to predict the occurrence of a CME, and to predict their subsequent evolution, depends critically on understanding the dominant physical processes which occur in the corona, and on understanding the medium through which CMEs propagate - the solar wind. In understanding the solar wind and CMEs, the extended inner corona is a critical region. This complex region starts at the solar surface and extends to where the coronal plasma starts to expand radially and becomes supersonic. Current observations of this region are very limited. There are a handful of broadband visible light coronagraphs which provide rather noisy measurements of the Thomson-scattered light from coronal electrons such as the COR1/STEREO coronagraphs, or the MLSO MKIV coronameters (to be upgraded to COSMO soon). Current EUV imagers and spectrometers provide very high-quality data, but their field of view is typically limited to a few tenths of solar radii from the photosphere at best. There is no spectrometer currently in use which can observe the corona above a few tenths of a solar radius from the limb, severely restricting efforts to understand the source region of CMEs and the solar wind.The goal of the proposed spectrometer is to capitalize on the diagnostic properties of coronal forbidden emission lines in the visible and near-IR, to infer electron temperatures, ion densities, elemental abundances and charge states, bulk flow speeds, non-thermal heating (i.e. wave heating) and indirectly the properties of the coronal magnetic field. The scientific advantage of observing these lines stems primarily from the strength of their radiatively excited component, which enables the emission to extend out to large heliocentric distances. It is surprising therefore that observations of forbidden coronal emission lines in the visible have been seriously neglected in current solar missions. The proposed spectrometer directly addresses this shortcoming and will provide unique constraints on the physical processes that heat the solar atmosphere to over one million degrees and accelerate the solar wind.