On Stellar Coronae and Solar Active Regions
On Stellar Coronae and Solar Active Regions
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关于恒星日冕和太阳活动区域
DOI：
10.1086/317820
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
A. Maggio
中科院分区：
文献类型：
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作者：
J. Drake;G. Peres;S. Orlando;J. Laming;A. Maggio
基于1992年1月6日获得的Yohkoh软X射线望远镜（SXT）对太阳活动峰值附近的观测结果，我们寻找具有发射测量分布EM（T）的日冕结构，该分布与从极紫外探测器光谱观测中获得的中等活动恒星K2 Eri（K2 V）和K8 Boo A（G8 V）的观测到的恒星日冕发射测量分布相匹配。我们发现，所观察到的恒星分布EM（T）的峰值的温度，以及它们在温度范围6.0 μ log T μ 6.5内的斜率，与1992年1月6日SXT图像中获得的太阳活动区中最亮的那些非常相似。所观测到的斜率近似对应于β ~ 4的EM Δ Tβ，这比静态均匀加热回路模型预测的要陡得多。还观察到，在Escheri和EscherBoo A的日冕中的等离子体密度基本上与太阳活动区典型的等离子体密度相同。这些数据提供了迄今为止最好的观测支持，支持了这样一个假设，即活动水平达到K2 V和K2 V的类太阳恒星主要由类似于太阳上观测到的活动区域所主导，尽管可能比太阳上观测到的活动区域大得多。解释观测到的恒星辐射测量所需的明亮活动区的表面填充因子近似为1。我们推测，在这种情况下，小规模的“纳米火焰”主导了活动区域的加热，其活动水平与K2 V和K2 B的活动水平相似。在更高的活动水平下，活动区域本身的相互作用可能导致更大尺度上的耀斑增加，这是导致等离子体加热到非常活跃的恒星上观测到的日冕温度T = 107 K的原因。使用比现有仪器更灵敏的仪器观测X射线和极紫外光变曲线，同时确定整个日冕温度范围内的等离子体密度（106-107 K及更高），对于确认耀斑加热假设并获取有关类似太阳活动区温度下日冕结构的进一步细节非常重要（T <$5 × 106 K）和最活跃恒星的温度（T <$107 K）。
Based on Yohkoh Soft X-Ray Telescope (SXT) observations of the Sun near peak activity level obtained on 1992 January 6, we search for coronal structures that have emission measure distributions EM(T) that match the observed stellar coronal emission measure distributions derived for the intermediate-activity stars ϵ Eri (K2 V) and ξ Boo A (G8 V) from Extreme Ultraviolet Explorer spectroscopic observations. We find that the temperatures of the peaks of the observed stellar distributions EM(T), as well as their slopes in the temperature range 6.0 ≲ log T ≲ 6.5, are very similar to those obtained for the brightest of the solar active regions in the 1992 January 6 SXT images. The observed slopes correspond approximately to EM ∝ Tβ with β ~ 4, which is much steeper than predicted by static, uniformly heated loop models. Plasma densities in the coronae of ϵ Eri and ξ Boo A are also observed to be essentially the same as the plasma densities typical of solar active regions. These data provide the best observational support yet obtained for the hypothesis that solar-like stars up to the activity levels of ϵ Eri (K2 V) and ξ Boo A are dominated by active regions similar to, though possibly considerably larger than, those observed on the Sun. The surface filling factor of bright active regions needed to explain the observed stellar emission measures is approximately unity. We speculate on the scenario in which small-scale "nanoflares" dominate the heating of active regions up to activity levels similar to those of ϵ Eri (K2 V) and ξ Boo A. At higher activity levels still, the interactions of the active regions themselves may lead to increasing flaring on larger scales that is responsible for heating plasma to the observed coronal temperatures of T ≳ 107 K on very active stars. Observations of X-ray and EUV light curves using more sensitive instruments than are currently available, together with determinations of plasma densities over the full range of coronal temperatures (106-107 K and higher), will be important to confirm flare heating hypotheses and to elicit further details concerning coronal structures at solar-like active region temperatures (T ≲ 5 × 106 K) and the temperatures that characterize the most active stars (T ≳ 107 K).