A New Measurement of the Electron Density in the Local Interstellar Medium
A New Measurement of the Electron Density in the Local Interstellar Medium
复制标题
局部星际介质中电子密度的新测量
DOI：
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
J. Linsky
中科院分区：
文献类型：
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作者：
B. Wood;J. Linsky
利用戈达德高分辨摄谱仪中的中阶梯光栅，我们观测到了附近（d = 13.3pc）的星星系统卡佩拉（G8 III + G1 III）的C Ⅱ λλ1335，1336发射线。在两条恒星发射线中都检测到了星际C II吸收特征。从这些吸收线导出的基态和激发态C II柱密度意味着在局域星际介质（LISM）中的电子密度为ne = 0.11+ 0.12−0.06 cm-3。与以前的推导NE从镁II/镁I的比例，建议的C II线的密度是独立的电离平衡的假设。LISM中的H I密度的当前估计在0.1- 0.2cm-3的范围内。根据极紫外探测器的数据，距离卡佩拉仅7°的白色矮星G191-B2B的He I/H I比值为0.068-0.082。这些结果表明氢和氦朝向卡佩拉的电离分数分别为X（H）= 0.45 ± 0.25和X（He）= 0.57 ± 0.23，证实氢和氦在LISM中基本上被电离。
Using the echelle-A grating of the Goddard High-Resolution Spectrograph, we have observed the C II λλ1335, 1336 emission lines of the nearby (d = 13.3 pc) star system Capella (G8 III + G1 III). Interstellar C II absorption features are detected within both stellar emission lines. The ground-state and excited-state C II column densities derived from these absorption lines imply an electron density of ne = 0.11+ 0.12−0.06 cm-3 in the local interstellar medium (LISM). Unlike previous derivations of ne from Mg II/Mg I ratios, the density suggested by the C II lines is independent of assumptions about ionization equilibrium. Current estimates of the H I density in the LISM are in the range 0.1-0.2 cm-3. The He I/H I ratio toward the white dwarf G191-B2B, which is only 7° from Capella, has been measured to be He I/H I = 0.068-0.082 from the Extreme-Ultraviolet Explorer data. These results indicate hydrogen and helium ionization fractions toward Capella of X(H) = 0.45 ± 0.25 and X(He) = 0.57 ± 0.23, respectively, confirming that hydrogen and helium are substantially ionized in the LISM.