Response of optical hydrogen lines to beam heating I. Electron beams
Response of optical hydrogen lines to beam heating I. Electron beams
复制标题
光学氢谱线对束流加热的响应 I. 电子束
DOI：
10.1051/0004-6361/200811559
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发表时间：
2009
影响因子：
6.5
通讯作者：
Z. Moravec
中科院分区：
文献类型：
--
作者：
J. Kašparová;M. Varady;P. Heinzel;M. Karlický;Z. Moravec
上下文太阳耀斑中氢巴耳末线的观测仍然是耀斑脉冲阶段色球层耀斑过程的重要信息来源。光学厚氢线的强度分布由燃烧大气的温度、密度和电离结构、等离子体速度和线形成区域中粒子的速度分布决定。目标。我们研究了非热电子在H α、H β和H γ谱线形成区中的作用，以揭示它们对这些谱线形成的影响。我们专注于脉冲束加热在亚秒级的时间尺度上变化。此外，我们从理论上探讨了一种新的诊断工具存在的可能性，表明存在的非热电子在耀斑色球光学氢线的基础上的观测。方法.为了模拟燃烧的大气和随时间变化的氢激发和电离的演变，我们使用了1-D辐射流体动力学代码结合测试粒子代码，模拟幂律电子束的传播，散射和热化，以获得耀斑加热和非热碰撞率由于与氢原子的相互作用的光束。为了不受其他影响而使结果产生偏差，我们只计算了耀斑大气的短时演化，而忽略了辐射传输中的等离子体速度。结果所有计算的模型都显示了亚秒级时间尺度上的模拟巴耳末线强度的时间相关响应，与亚秒级的光束通量后面的时滞。取决于光束参数，线中心和翼都可以显示出明显的强度变化。非热碰撞率通常导致色球层中形成的次级区域的发射增加。结论.尽管非热电子束对巴耳末线强度分布有明显的影响，但我们无法根据我们的模拟来产生任何明确的非热电子在线发射区域中的诊断，这将基于对各个巴耳末线强度分布的比较。然而，快速线强度的变化，以及相关的光束通量的变化，代表了脉动光束的间接指示。
Context. Observations of hydrogen Balmer lines in solar flares remain an important source of information on flare processes in the chromosphere during the impulsive phase of flares. The intensity profiles of optically thick hydrogen lines are determined by the temperature, density, and ionisation structure of the flaring atmosphere, by the plasma velocities and by the velocity distribution of particles in the line formation regions. Aims. We investigate the role of non-thermal electrons in the formation regions of H α , H β , and H γ lines in order to unfold their influence on the formation of these lines. We concentrate on pulse-beam heating varying on a subsecond timescale. Furthermore, we theoretically explore possibility that a new diagnostic tool exists indicating the presence of non-thermal electrons in the flaring chromosphere based on observations of optical hydrogen lines. Methods. To model the evolution of the flaring atmosphere and the time-dependent hydrogen excitation and ionisation, we used a 1-D radiative hydrodynamic code combined with a test-particle code that simulates the propagation, scattering, and thermalisation of a power-law electron beam in order to obtain the flare heating and the non-thermal collisional rates due to the interaction of the beam with the hydrogen atoms. To not bias the results by other effects, we calculate only short time evolutions of the flaring atmosphere and neglect the plasma velocities in the radiative transfer. Results. All calculated models have shown a time-correlated response of the modelled Balmer line intensities on a subsecond timescale, with a subsecond timelag behind the beam flux. Depending on the beam parameters, both line centres and wings can show pronounced intensity variations. The non-thermal collisional rates generally result in an increased emission from a secondary region formed in the chromosphere. Conclusions. Despite the clear influence of the non-thermal electron beams on the Balmer line intensity profiles, we were not able on the basis of our simulations to produce any unambiguous diagnostic of non-thermal electrons in the line-emitting region, which would be based on comparison of individual Balmer line intensity profiles. However, fast line intensity variations, well-correlated with the beam flux variations, represent an indirect indication of pulsating beams.