LABORATORY MEASUREMENTS OF WHITE DWARF PHOTOSPHERIC SPECTRAL LINES: Hβ
LABORATORY MEASUREMENTS OF WHITE DWARF PHOTOSPHERIC SPECTRAL LINES: Hβ
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白矮星光球谱线的实验室测量：Hβ
DOI：
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
T. Nagayama
中科院分区：
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作者：
R. E. Falcon;G. Rochau;J. Bailey;T. Gomez;M. Montgomery;D. Winget;T. Nagayama
我们用光谱法测量了实验室等离子体中多个氢原子的巴耳末谱线，以研究白色矮星（WD）大气模型中的理论谱线。桑迪亚国家实验室的Z脉冲功率装置产生的X射线辐射在充满氢气的气室中启动等离子体形成，复制WD光球条件。在这里，我们提出了Hβ的时间分辨测量，并使用不同的理论线轮廓来拟合这条线，以诊断电子密度ne和n = 2能级布居n2。通过综合测试，我们表征了该实验平台的诊断方法的有效性。在一次实验中，我们推断出在我们的等离子体的120 ns演化过程中，电子密度的连续范围从Ne 104 × 1016 cm−3增加到1030 × 1016 cm−3。此外，我们观察到n2最初相对于局部热力学平衡（LTE）升高，然后在1055 ns内平衡，与LTE保持一致。这支持了我们在这段时间后对Te的电子温度测定为1.3 eV（15，000 K）。在ne = 1017 cm−3处，我们发现基于计算机模拟的线轮廓计算比WD天文学界目前使用的线轮廓提供了更好的拟合（降低的χ2）。然而，推断的条件是在良好的定量协议。这项工作为今后研究不同氢原子巴耳末谱线之间的相对形状和强度奠定了实验基础。
We spectroscopically measure multiple hydrogen Balmer line profiles from laboratory plasmas to investigate the theoretical line profiles used in white dwarf (WD) atmosphere models. X-ray radiation produced at the Z Pulsed Power Facility at Sandia National Laboratories initiates plasma formation in a hydrogen-filled gas cell, replicating WD photospheric conditions. Here we present time-resolved measurements of Hβ and fit this line using different theoretical line profiles to diagnose electron density, ne, and n = 2 level population, n2. Aided by synthetic tests, we characterize the validity of our diagnostic method for this experimental platform. During a single experiment, we infer a continuous range of electron densities increasing from ne ∼ 4 to ∼30 × 1016 cm−3 throughout a 120-ns evolution of our plasma. Also, we observe n2 to be initially elevated with respect to local thermodynamic equilibrium (LTE); it then equilibrates within ∼55 ns to become consistent with LTE. This supports our electron-temperature determination of Te ∼ 1.3 eV (∼15,000 K) after this time. At ne ≳ 1017 cm−3, we find that computer-simulation-based line-profile calculations provide better fits (lower reduced χ2) than the line profiles currently used in the WD astronomy community. The inferred conditions, however, are in good quantitative agreement. This work establishes an experimental foundation for the future investigation of relative shapes and strengths between different hydrogen Balmer lines.