Three years in the coronal life of AB Dor I. Plasma emission measure distributions and abundances at different activity levels
Three years in the coronal life of AB Dor I. Plasma emission measure distributions and abundances at different activity levels
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AB Dor I 日冕生命的三年。等离子体发射测量不同活动水平下的分布和丰度
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
G. Micela
中科院分区：
文献类型：
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作者：
J. Sanz;A. Maggio;G. Micela
在过去的三年里，xmm -牛顿和钱德拉天文台对年轻的活跃恒星AB Dor （K1 IV-V）进行了16次观测，总共获得了650千米的高分辨率x射线光谱。选取平均辐射水平最高和最低的XMM/RGS观测资料，研究了AB Dor在两种不同活动水平下的日冕性质。我们使用相同的基于线的分析技术，将基于XMM数据的结果与从更高分辨率的Chandra/HETG光谱获得的结果进行了比较。我们重建了在对数T (K) 6:1-7.6范围内的等离子体发射测量分布与温度（EMD），并确定了AB Dor的日冕丰度，获得了两种仪器之间一致的结果。EMD的整体形状也与之前从EUVE数据推断出的形状一致。EMD在log T (K) 6:9处急剧增加，达到峰值，在log T (K) 6:9-7.3范围内出现大量等离子体。相对于太阳光球值，日冕丰度表现出明显的耗竭趋势，对于第一电离势（FIP）增加的元素，直到Fe值（(Fe/H)= -0.57），然后对于更高FIP的元素，光球值逐渐恢复。He-like三重态和fexxi线和fexxi线比值表明，在logt (K) 6:3a和logt (K) 7下，电子密度分别为logne 10.8 cm3和logne 12.5 cm3，表明等离子体压力随着温度的升高而急剧增加。这些结果是在一个由不同种类的磁环结构组成的日冕的框架中解释的，它比恒星半径短，在等压条件下，压力随着最高等离子体温度的增加而增加，并且占据了恒星表面的一小部分（f10.4 - 10.6）。
The young active star AB Dor (K1 IV-V) has been observed 16 times in the last three years with the XMM-Newton and Chandra observatories, totalling 650 ks of high-resolution X-ray spectra. The XMM/RGS observations with the highest and lowest average emission levels have been selected to study the coronal properties of AB Dor in two dierent activity levels. We compare the results based on the XMM data with those obtained from a higher resolution Chandra/HETG spectrum, using the same line-based analysis technique. We have reconstructed the plasma Emission Measure Distribution vs. temperature (EMD) in the range log T (K) 6:1-7.6, and we have determined the coronal abundances of AB Dor, obtaining consistent results between the two instruments. The overall shape of the EMD is also consistent with the one previously inferred from EUVE data. The EMD shows a steep increase up to the peak at log T (K) 6:9 and a substantial amount of plasma in the range log T (K) 6:9-7.3. The coronal abundances show a clear trend of increasing depletion with respect to solar photospheric values, for elements with increasing First Ionization Potential (FIP), down to the Fe value ((Fe/H)= -0.57), followed by a more gradual recovery of the photospheric values for elements with higher FIP. He-like triplets and Fe xxi and Fexxii lines ratios indicate electron densities log ne 10: 8c m 3 at log T (K) 6: 3a nd logne 12: 5c m 3 at log T (K) 7, implying plasma pressures steeply increasing with temperature. These results are interpreted in the framework of a corona composed of dierent families of magnetic loop structures, shorter than the stellar radius and in isobaric conditions, having pressures increasing with the maximum plasma temperature, and which occupy a small fraction (f 10 4 -10 6 ) of the stellar surface.