Spectral Line Selection for HMI: A Comparison of Fe I 6173 Å and Ni I 6768 Å

摘要: We present a study of two spectral lines, Fe I 6173 A and Ni 6768 A, that were candidates to be used in the Helioseismic Magnetic Imager (HMI) for observing Doppler velocity vector magnetic field. The line profiles studied using Mt. Wilson Observatory, Advanced Stokes Polarimeter Kitt Peak-McMath Pierce telescope one-meter Fourier transform spectrometer atlas. Both have clean continua no blends threaten instrument performance. is 2% deeper, 15% narrower, has 6% smaller equivalent width than line. potential each recover pre-assigned solar conditions tested least-squares minimization technique fit Milne-Eddington models tens thousands been sampled at five positions across Overall, better performance vector-magnetic-field retrieval. Specifically, able determine field strength, longitudinal transverse flux four times more accurately active regions. Inclination azimuthal angles can recovered ≈2° above 600 Mx cm−2 1000 I. Therefore, determines magnetic-field orientation plage, whereas both lines provide good determination penumbrae umbrae. selected use HMI due its diagnostics while not sacrificing information. one exception arises when high strengths combine with velocities move beyond effective sampling range. higher geff means useful range values regions strong