Implications from Extreme-Ultraviolet Observations for Coronal Heating of Active Stars
Implications from Extreme-Ultraviolet Observations for Coronal Heating of Active Stars
复制标题
极紫外观测对活跃恒星日冕加热的影响
DOI：
10.1086/311907
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发表时间：
1999
期刊：
影响因子：
--
通讯作者：
E. Guinan
中科院分区：
文献类型：
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作者：
M. Audard;M. Güdel;E. Guinan
利用极紫外探测器（EUVE）对两个活跃的太阳类似物47 Cas和EK Dra的耀斑统计数据和耀斑发生率在能量上的分布进行了研究。EUVE卫星对每颗恒星进行了近7天的观测。同时从它的光谱仪获得的光谱数据被用来得出它们日冕的温度和丰度特征。通过对光谱进行光学薄热模型拟合，得到了不同发射量分布的发射模型。采用不同的时间分类方法对深测仪器的光子表进行了分析。共有28个耀斑被确定供进一步分析。时间研究提供了每次耀斑总辐射能量损失的估计值。在3×1033 ~ 6×1034 ergs能量范围内，耀斑在x射线总能量中的微分分布符合幂律（dN/dE∝E−α, α≈2.2±0.2）。幂律指数比典型太阳耀斑的指数大，但与最近发现的小规模太阳事件的指数相似。如果幂律继续适用于中等太阳耀斑的能量，那么所有耀斑集合发出的总能量可能足以解释所有观测到的两颗恒星的耀斑和“静止”x射线发射。因此，加热日冕所需的能量，即使不是全部，也有相当一部分可以由耀斑提供。
Extreme Ultraviolet Explorer (EUVE) data of two active solar analogs, 47 Cas and EK Dra, were used to investigate flare statistics and the distribution of the flare occurrence rate in energy. The EUVE satellite observed each star for almost 7 days. Simultaneous spectral data from its spectrometers were used to derive temperature and abundance characteristics of their coronae. The emission models were derived from differential emission measure distributions by fitting optically thin thermal models to the spectra. The Deep Survey instrument photon lists were analyzed by applying different time binnings. A total of 28 flares were identified for further analysis. The timing study provided estimates for the total radiative energy loss of each flare. The differential distribution of flares in total X-ray energy is found to be a power law (dN/dE∝E−α, with α≈2.2±0.2) valid in the energy range between 3×1033 and 6×1034 ergs. The power-law index is larger than that for typical solar flares but is similar to indices found recently for small-scale solar events. If the power law continues to energies of moderate solar flares, then the total energy emitted by the ensemble of all flares may suffice to explain all of the observed flaring and "quiescent" X-ray emissions of the two stars. A considerable portion, if not all, of the energy required to heat their coronae could thus be provided by flares.