SDO/HMI Linewidth Data

The linewidth observable refers to the FWHM of the (assumed) Gaussian absorption line profile for the 6173.3 Å line on the surface of the sun.

HMI samples the Fe I absorption line at 6173.3 Å at six points. Assuming that the "pure" solar Fe I line profile is a Gaussian, and the HMI filter filter transmission profiles are delta functions, the first and second Fourier coefficients of the of the Fe I line can be calculated and an estimate of the Doppler Velocity can be made. An estimate (proxy) for the continuum intensity Ic is obtained by "reconstructing" the solar line from the estimates of the Doppler shift λo, the linewidth σ, and the linedepth Id. More details can be found at http://jsoc.stanford.edu/relevant_papers/observables.pdf.

可观测的线宽指的是太阳表面6173.3 Å线（假定）高斯吸收线型轮廓的全宽半高（FWHM）。太阳磁场成像仪（HMI）在6173.3 Å处对Fe I吸收线进行六点采样。在假定“纯净”的太阳Fe I线型轮廓为高斯分布，且HMI滤光片的滤光传输轮廓为δ函数的前提下，可以计算出Fe I线的首阶和二阶傅里叶系数，并据此估算多普勒速度。通过对多普勒移位λo、线宽σ以及线深度Id的估计，对连续强度Ic的估算（代理值）可通过重建太阳线谱而获得。更详细的资料可参考http://jsoc.stanford.edu/relevant_papers/observables.pdf。