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arXiv 1003.4128astro-ph.SR
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狮子座CN上巨大耀斑的多波长观测。日冕性质的时间演化

Multiwavelength observations of a giant flare on CN Leonis III. Temporal evolution of coronal properties

Carolin Liefke, Birgit Fuhrmeister, Juergen H. M. M. Schmitt

摘要:

恒星耀斑影响从光球层到色球层和过渡区到日冕的所有大气层。在不同光谱波段同时进行观测,可以全面了解耀斑不同阶段的环境条件和物理过程。利用VLT和XMM-Newton的UVES光谱仪同时观测了活动M矮星CN Leo的一次大耀斑期间日冕等离子体的性质,分析了日冕温度和辐射测量的时间演化,并研究了耀斑期间电子密度和日冕丰度的变化。光学Fe XIII线发射跟踪较冷的静态电晕。虽然持续时间很短(指数衰减时间< 5分钟),但耀斑峰值的X射线通量超过了静止水平的100倍。整个耀斑的平均电子密度大于5 * 10^11 cm^-3。耀斑等离子体显示出铁的增强的一个因素约。2在耀斑的上升和峰值阶段。我们从耀斑上升、峰值和衰减过程中发射等离子体的演化得出耀斑结构的尺寸小于9000 km。耀斑等离子体的特征表明,耀斑起源于一个紧凑的拱廊,而不是一个单一的环。X射线和光学数据的综合结果进一步限制了不同大气层中等离子体的性质和耀斑结构的几何形状。

英文摘要:

Stellar flares affect all atmospheric layers from the photosphere over chromosphere and transition region up into the corona. Simultaneous observations in different spectral bands allow to obtain a comprehensive picture of the environmental conditions and the physical processes going on during different phases of the flare. We investigate the properties of the coronal plasma during a giant flare on the active M dwarf CN Leo observed simultaneously with the UVES spectrograph at the VLT and XMM-Newton.From the X-ray data, we analyze the temporal evolution of the coronal temperature and emission measure, and investigate variations in electron density and coronal abundances during the flare. Optical Fe XIII line emission traces the cooler quiescent corona. Although of rather short duration (exponential decay time < 5 minutes), the X-ray flux at flare peak exceeds the quiescent level by a factor of 100. The electron density averaged over the whole flare is greater than 5 * 10^11 cm^-3. The flare plasma shows an enhancement of iron by a factor of approx. 2 during the rise and peak phase of the flare. We derive a size of <9000 km for the flaring structure from the evolution of the the emitting plasma during flare rise, peak, and decay. The characteristics of the flare plasma suggest that the flare originates from a compact arcade instead of a single loop. The combined results from X-ray and optical data further confine the plasma properties and the geometry of the flaring structure in different atmospheric layers.

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