The Structure of Stellar Coronae in Active Binary Systems
The Structure of Stellar Coronae in Active Binary Systems
复制标题
活跃双星系统中的星冕结构
DOI：
10.1086/345815
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
Palermo
中科院分区：
文献类型：
--
作者：
J. Sanz;N. Brickhouse;A. B. H. C. F. Astrophysics;Cambridge;I. A. D. Palermo;Palermo
利用极紫外光谱对28颗恒星（22颗活动双星系统，外加6颗单星或宽双星作为比较）进行了观测，从发射测度分布（EMD）、电子密度和尺度大小等方面建立了活动双星系统中恒星日冕的结构。样本中的恒星包括极紫外线探测卫星（EUVE）在9年运行期间获得的观测结果。EUVE数据允许使用铁发射线在log Te（K）= 5.6-7.4的范围内构造连续EMD。这些数据补充了IUE观测，以模拟较低的温度范围[log Te（K）= 4.0-5.6]。对EMD的观测显示了一个突出的狭窄增强，或者说是在25颗恒星的log Te（K）<$6.9附近的“隆起”，这定义了一个基本的日冕结构。单位恒星面积的辐射量随目标恒星轨道（或光度）周期的增加而减少;双星系统中的恒星在日冕温度下通常比缓慢旋转的单星有更多的物质。对于某些靶，高电子密度（Ne = 1012 cm-3）在Te（K）= 7.0时得到，这意味着小的发射体积。观测结果表明，这些恒星的磁冕与两类基本的磁环相一致：最高温度在log Te（K）<$6.3附近，电子密度较低（Ne <$109 -1010.5 cm-3）的类太阳磁环，以及最高温度在log Te（K）<$6.9附近，电子密度较高（Ne <$1012 cm-3）的较热磁环。对于最活跃的恒星，物质也存在于更高的温度[log Te（K）≥ 6.9]。然而，目前的从头算恒星环模型不能再现这样的配置。对这些系统的光变曲线的分析揭示了日冕物质旋转的特征，以及明显的季节性（即，年变化（活动水平）。
A survey of 28 stars (22 active binary systems, plus six single stars or wide binaries for comparison) using extreme ultraviolet spectra has been conducted to establish the structure of stellar coronae in active binary systems from the emission measure distribution (EMD), electron densities, and scale sizes. Observations obtained by the Extreme Ultraviolet Explorer satellite (EUVE) during 9 years of operation are included for the stars in the sample. EUVE data allow a continuous EMD to be constructed in the range log Te(K) ∼ 5.6-7.4, using iron emission lines. These data are complemented with IUE observations to model the lower temperature range [log Te(K) ∼ 4.0-5.6]. Inspection of the EMD shows an outstanding narrow enhancement, or "bump" peaking around log Te(K) ∼ 6.9 in 25 of the stars, defining a fundamental coronal structure. The emission measure per unit stellar area decreases with increasing orbital (or photometric) periods of the target stars; stars in binaries generally have more material at coronal temperatures than slowly rotating single stars. High electron densities (Ne ≳ 1012 cm-3) are derived at ∼log Te(K) ∼ 7.0 for some targets, implying small emitting volumes. The observations suggest the magnetic stellar coronae of these stars are consistent with two basic classes of magnetic loops: solar-like loops with maximum temperature around log Te(K) ∼ 6.3 and lower electron densities (Ne ≳ 109-1010.5 cm-3), and hotter loops peaking around log Te(K) ∼ 6.9 with higher electron densities (Ne ≳ 1012 cm-3). For the most active stars, material exists at much higher temperatures [log Te(K) ≥ 6.9] as well. However, current ab initio stellar loop models cannot reproduce such a configuration. Analysis of the light curves of these systems reveals signatures of rotation of coronal material, as well as apparent seasonal (i.e., year-to-year) changes in the activity levels.