Spectropolarimetric NLTE inversion code SNAPI
Spectropolarimetric NLTE inversion code SNAPI
复制标题
分光偏振 NLTE 反演码 SNAPI
DOI：
--
复制
发表时间：
2018
影响因子：
6.5
通讯作者：
M. Noort
中科院分区：
文献类型：
--
作者：
I. Milić;M. Noort
上下文反演代码是将模型大气与观测到的斯托克斯光谱拟合的计算机程序，从而反演相关的大气参数。在太阳色球层，光谱线是由散射形成的，需要开发，测试和比较新的非局部热平衡（NLTE）反演代码的兴趣日益增加。
目标。我们提出了一个新的NLTE反演代码，是基于响应函数的分析计算。我们将代码命名为SNAPI，这是光谱偏振NLTE分析动力反演的缩写。
方法. SNAPI反演完整的斯托克斯光谱，以获得温度，速度和磁场矢量的深度相关分层。它基于所谓的节点方法，其中大气参数在大气中的几个固定点自由变化，并假设其表现为之间的样条。我们描述了一般的反演方法和我们在实现中所做的具体选择。
结果我们测试的性能上的一个学术问题和两个有趣的NLTE的例子，钙II 8542和钠I D谱线。该代码被发现具有良好的收敛性能，并优于基于有限差分的代码在这个特定的实现至少三个因素。我们反演了一小部分模拟太阳大气中Na线的合成观测，并得出结论，Na线可靠地反演了−3 <logτ <−0.5范围内的磁场和速度。
Context. Inversion codes are computer programs that fit a model atmosphere to the observed Stokes spectra, thus retrieving the relevant atmospheric parameters. The rising interest in the solar chromosphere, where spectral lines are formed by scattering, requires developing, testing, and comparing new non-local thermal equilibrium (NLTE) inversion codes.
Aims. We present a new NLTE inversion code that is based on the analytical computation of the response functions. We named the code SNAPI, which is short for spectropolarimetic NLTE analytically powered inversion.
Methods. SNAPI inverts full Stokes spectrum in order to obtain a depth-dependent stratification of the temperature, velocity, and the magnetic field vector. It is based on the so-called node approach, where atmospheric parameters are free to vary in several fixed points in the atmosphere, and are assumed to behave as splines in between. We describe the inversion approach in general and the specific choices we have made in the implementation.
Results. We test the performance on one academic problem and on two interesting NLTE examples, the Ca II 8542 and Na I D spectral lines. The code is found to have excellent convergence properties and outperforms a finite-difference based code in this specific implementation by at least a factor of three. We invert synthetic observations of Na lines from a small part of a simulated solar atmosphere and conclude that the Na lines reliably retrieve the magnetic field and velocity in the range −3 < logτ < −0.5.