Convective blueshifts in the solar atmosphere
Convective blueshifts in the solar atmosphere
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太阳大气中的对流蓝移
DOI：
10.1051/0004-6361/201834538
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发表时间：
2019
影响因子：
6.5
通讯作者：
Ronald
中科院分区：
文献类型：
--
作者：
Franziska;Löhner-Böttcher;Johannes;Schmidt;Wolfgang;Steinmetz;Holzwarth;Ronald
太阳大气中的对流运动导致光谱线变得不对称并在波长上移动。对光球谱线而言，这种差分多普勒频移从太阳盘中心到边缘是变化的。目的对对流蓝移及其中心到边缘的变化进行精确和全面的观测，提高我们对大气流体动力学和随后的谱线形成的理解，方法我们对宁静太阳的对流蓝移进行了系统的光谱测量，德国真空塔望远镜的激光绝对参考光谱仪（LARS）。太阳圆盘的空间扫描覆盖了11个日心位置，每个位置沿着四个径向（赤道和赤道）轴。在可见光范围内的26条光球到色球线的高分辨率光谱用激光频率梳以1 ms− 1的精度校准到绝对波长。应用星历和参考校正，平分线分析提供了线不对称性和多普勒频移，其不确定性只有几ms-1。为了允许与其他观测的比较，我们卷积的结果，以降低光谱resolutions.ResultsAll谱线平分线表现出系统的中心到肢体的变化。通常，盘中心的蓝移“C”形曲线会向太阳边缘转变为蓝移较少的“\”形。所有线的比较揭示了对流蓝移线深度的系统依赖性。线最小值的蓝移描述了随着线深度的增加而线性减小。中心到边缘变化的斜率在日心位置μ= 0.7和0.85之间形成了一个反转点，这被看作是光球层中部水平颗粒流的影响。在光球上层至色球层形成的谱线极小值几乎没有蓝移，甚至有轻微的红移。合成模型产生相当大的偏差，从所观察到的中心到肢体variation.ConclusionsThe得到的多普勒频移的安静的太阳可以作为一个绝对的参考其他意见，多普勒的相对校准，和必要的改进大气模型。在此基础上，恒星表面对流的高精度模型的开发将通过径向速度测量推进对（潜在可居住的）系外行星的探测。
ContextConvective motions in the solar atmosphere cause spectral lines to become asymmetric and shifted in wavelength. For photospheric lines, this differential Doppler shift varies from the solar disk center to the limb.AimsPrecise and comprehensive observations of the convective blueshift and its center-to-limb variation improve our understanding of the atmospheric hydrodynamics and ensuing line formation, and provide the basis to refine 3D models of the solar atmosphere.MethodsWe performed systematical spectroscopic measurements of the convective blueshift of the quiet Sun with the Laser Absolute Reference Spectrograph (LARS) at the German Vacuum Tower Telescope. The spatial scanning of the solar disk covered 11 heliocentric positions each along four radial (meridional and equatorial) axes. The high-resolution spectra of 26 photospheric to chromospheric lines in the visible range were calibrated with a laser frequency comb to absolute wavelengths at the 1 ms− 1 accuracy. Applying ephemeris and reference corrections, the bisector analysis provided line asymmetries and Doppler shifts with an uncertainty of only few ms− 1. To allow for a comparison with other observations, we convolved the results to lower spectral resolutions.ResultsAll spectral line bisectors exhibit a systematic center-to-limb variation. Typically, a blueshifted “C”-shaped curve at disk center transforms into a less blueshifted “\”-shape toward the solar limb. The comparison of all lines reveals the systematic dependence of the convective blueshift on the line depth. The blueshift of the line minima describe a linear decrease with increasing line depths. The slope of the center-to-limb variation develops a reversal point at heliocentric positions between µ= 0.7 and 0.85, seen as the effect of horizontal granular flows in the mid photosphere. Line minima formed in the upper photosphere to chromosphere exhibit hardly any blueshift or even a slight redshift. Synthetic models yield considerable deviations from the observed center-to-limb variation.ConclusionsThe obtained Doppler shifts of the quiet Sun can serve as an absolute reference for other observations, the relative calibration of Dopplergrams, and the necessary refinement of atmospheric models. Based on this, the development of high-precision models of stellar surface convection will advance the detection of (potentially habitable) exoplanets by radial velocity measurements.
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DOI：
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发表时间：
1982
期刊：
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作者：
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R. Volkmer