Stellar Coronal Abundances at Intermediate-Activity Levels: ξ UMa
Stellar Coronal Abundances at Intermediate-Activity Levels: ξ UMa
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中等活动水平的恒星日冕丰度： Ψ UMa
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
D. García
中科院分区：
文献类型：
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作者：
B. Ball;J. Drake;L. Lin;V. Kashyap;J. Laming;D. García
我们提出了一个分析钱德拉高能量传输光栅（HETG）光谱的日冕的关键中间活动，四重恒星系统的UMA。使用最大的A/B子系统分离在2001年，我们试图解决第一次在X射线的两个组成部分，使用HETG中能光栅（MEG）。我们发现系统的Aa分量比Bb分量暗至少2个数量级。我们使用马尔可夫链蒙特卡罗方法重建差分发射措施（DEM）和丰度，并讨论第一电离势（FIP）的问题。重建的DEM显示出两个明显的峰值，分别在log T = 6.5和log T = 7.0 K，类似于更明亮的太阳活动区。日冕丰度相对于恒星光球层与FIP的关系图显示，UMA的FIP行为介于较活跃恒星和较不活跃恒星之间，与其X射线光度相称。镁、铁和硅的丰度都在太阳之下，其中铁的丰度最低。低FIP元素Na和Al具有相似的丰度，并且它们都高于Mg、Fe和Si组。丰度在S处最低，逐渐上升到Ne，高于光球层，正如其他作者在类似恒星上看到的那样。这里看到的一些FIP行为是由Laming的新有质动力模型预测的。
We present an analysis of Chandra High Energy Transmission Grating (HETG) spectra of the corona of the critical intermediate-activity, quadruple stellar system ξ UMa. Using the maximum A/B subsystem separation in 2001, we attempted to resolve for the first time in X-rays the two components using the HETG Medium Energy Grating (MEG). We found the Aa component of the system to be at least 2 orders of magnitude fainter than the Bb component. We used the Markov Chain Monte Carlo method to reconstruct differential emission measures (DEMs) and abundances and discuss first ionization potential (FIP) issues. The reconstructed DEMs showed two pronounced peaks at log T ≈ 6.5 and log T ≈ 7.0 K, respectively, similar to brighter solar active regions. A plot of coronal abundances, with respect to stellar photospheric, versus FIP reveals that the FIP behavior of ξ UMa is intermediate between less and more active stars, commensurate with its X-ray luminosity. The abundances of Mg, Fe, and Si are just subsolar, with Fe having the lowest abundance of these. The low-FIP elements Na and Al have similar abundances, and they are both higher than the Mg, Fe, and Si group. The abundances show a minimum at S, rising gradually to Ne, which is higher than photospheric, as has been seen by other authors on similar stars. Some of the FIP behavior seen here is predicted by the new ponderomotive force model of Laming.