太阳BaII 4554 A谱线的多普勒诊断：三维流体动力学模式中的NLTE分析
Solar BaII 4554 A line as Doppler diagnostics: NLTE analysis in 3D hydrodynamical model
摘要：
本文的目的是分析多普勒图和多普勒仪技术的有效性，多普勒诊断的太阳光球速度使用的BaII 4554 A线。这两种技术进行评估的NLTE辐射转移计算的BaII 4554 A线的三维流体动力学模型的太阳对流。我们考虑的情况下，空间未涂抹的配置文件和配置文件涂抹的地面观测的分辨率。我们发现：（i）斑点重建多普勒速度图在300公里左右的高度很好地再现了“真实”速度，但有强烈下行流的颗粒间通道除外，在这些通道中速度可能被高估。(ii)在原始的和降低的空间分辨率下，雷达仪的速度都很好地代表了整个光球的“真实”速度。从涂抹的Ball 4554 A线轮廓的内翼导出的速度比外翼的速度更可靠。只有在高空间分辨率下，计算的晶间区内翼速度才比模型速度低（甚至符号相反）。(iii)在模拟BaII 4554 A谱线剖面时应考虑NLTE效应。这种效应在晶粒间区域更为明显。我们的分析支持这样的观点，即多普勒技术应用于BaII 4554 A线是一个有价值的工具，多普勒诊断的中间光球周围300公里。应用于这条线的λ计技术为我们提供了一个很好的机会来“追踪”沿整个光球直到温度最低值和色球层下部的非热运动。
英文摘要：
The aim of this paper is to analyse the validity of the Dopplergram and lambda-meter techniques for the Doppler diagnostics of solar photospheric velocities using the BaII 4554 A line. Both techniques are evaluated by means of NLTE radiative transfer calculations of the BaII 4554 A line in a three-dimensional hydrodynamical model of solar convection. We consider the cases of spatially unsmeared profiles and the profiles smeared to the resolution of ground-based observations. We find that: (i) Speckle-reconstructed Dopplergram velocities reproduce the ``true'' velocities well at heights around 300 km, except for intergranular lanes with strong downflows where the velocity can be overestimated. (ii) The lambda-meter velocities give a good representation of the ``true'' velocities through the whole photosphere, both under the original and reduced spatial resolutions. The velocities derived from the inner wing of smeared BaII 4554 A line profiles are more reliable than those for the outer wing. Only under high spatial resolution does the inner wing velocities calculated in intergranular regions give an underestimate (or even a sign reversal) compared with the model velocities. (iii) NLTE effects should be taken into account in modelling the BaII 4554 A line profiles. Such effects are more pronounced in intergranular regions. Our analysis supports the opinion that the Dopplergram technique applied to the BaII 4554 A line is a valuable tool for the Doppler diagnostics of the middle photosphere around 300 km. The λ-meter technique applied to this line gives us a good opportunity to ``trace'' the non-thermal motions along the whole photosphere up to the temperature minimum and lower chromosphere.
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