The influence of NLTE effects in Fe I lines on an inverted atmosphere
The influence of NLTE effects in Fe I lines on an inverted atmosphere
复制标题
FI 线中 NLTE 效应对倒转大气的影响
DOI：
10.1051/0004-6361/201937041
复制
发表时间：
2019
影响因子：
6.5
通讯作者：
S. Solanki
中科院分区：
文献类型：
--
作者：
H. Smitha;R. Holzreuter;M. Noort;S. Solanki
语境。根据萨哈-玻尔兹曼统计，太阳大气中铁原子的紫外线超电离导致其能级布居的偏差。这导致它们的线轮廓在非局部热力学平衡（NLTE）条件下形成。当反演此类剖面以确定大气参数时，NLTE 效应通常被忽略，并调整其他量以补偿与 LTE 的偏差。
目标。我们研究了常规采用的 LTE 反演 NLTE 中形成的铁线如何低估或高估大气量，例如温度 (T)、视线速度 (vLOS)、磁场强度 (B) 和倾角 (γ)，而早期论文主要关注 T。我们的研究结果具有广泛的影响，因为太阳物理学中得出的许多结果都是基于 LTE 中进行的铁线反演。
方法。我们使用 3D 磁流体动力学模拟快照合成了 LTE 和 NLTE 中 FeI 6301.5 Å 和 6302.5 Å 线的斯托克斯剖面。然后，这些配置文件在 LTE 中被反转。我们将 LTE 剖面反演推断出的大气视为基准模型，并将其与 NLTE 剖面反演得出的大气进行比较。观察到的差异归因于 NLTE 效应。
结果。忽略 NLTE 效应会在倒置大气中引入误差。虽然 T 中的误差可能高达 13%，但在 vLOS 和 B 中，误差可能高达 50% 或以上。我们发现所有三个反转节点都存在这些错误。重要的是，它们不会因剖面的空间平均而退化。
结论。我们概述了忽略 NLTE 效应如何影响 T、 vLOS、B 和 γ 的值，这些值是通过反转 FeI 6300 Å 线对确定的，例如通过 Hinode/SOT/SP 观察到的。在颗粒、晶间通道、磁性元件以及基本上每个容易受到 NLTE 效应影响的区域都会发现错误。因此，为了准确确定大气量及其分层，考虑 NLTE 效应非常重要。
Context. Ultraviolet overionisation of iron atoms in the solar atmosphere leads to deviations in their level populations based on Saha-Boltzmann statistics. This causes their line profiles to form in non-local thermodynamic equilibrium (NLTE) conditions. When inverting such profiles to determine atmospheric parameters, the NLTE effects are often neglected and other quantities are tweaked to compensate for deviations from the LTE.
Aims. We investigate how the routinely employed LTE inversion of iron lines formed in NLTE underestimates or overestimates atmospheric quantities, such as temperature (T), line-of-sight velocity (vLOS), magnetic field strength (B), and inclination (γ) while the earlier papers have focused mainly on T. Our findings has wide-ranging consequences since many results derived in solar physics are based on inversions of Fe I lines carried out in LTE.
Methods. We synthesized the Stokes profiles of Fe I 6301.5 Å and 6302.5 Å lines in both LTE and NLTE using a snapshot of a 3D magnetohydrodynamic simulation. The profiles were then inverted in LTE. We considered the atmosphere inferred from the inversion of LTE profiles as the fiducial model and compared it to the atmosphere resulting from the inversion of NLTE profiles. The observed differences have been attributed to NLTE effects.
Results. Neglecting the NLTE effects introduces errors in the inverted atmosphere. While the errors in T can go up to 13%, in vLOS and B, the errors can go as high as 50% or above. We find these errors to be present at all three inversion nodes. Importantly, they survive degradation from the spatial averaging of the profiles.
Conclusions. We provide an overview of how neglecting NLTE effects influences the values of T, vLOS, B, and γ that are determined by inverting the Fe I 6300 Å line pair, as observed, for example, by Hinode/SOT/SP. Errors are found at the sites of granules, intergranular lanes, magnetic elements, and basically in every region susceptible to NLTE effects. For an accurate determination of the atmospheric quantities and their stratification, it is, therefore, important to take the NLTE effects into account.