A Study on Magnetic-sensitivity Wavelength Position of the Working Line Used by the Full-Disk Magnetograph onboard the Advanced Space based Solar Observatory (ASO-S/FMG)

TL;DR

This study identifies the optimal magnetic-sensitivity spectral positions of the Fe I 5234.19 A line used by the ASO-S FMG, balancing sensitivity for linear and circular polarization through analysis of theoretical, in-orbit, and experimental data.

Contribution

It provides the first comprehensive analysis of the magnetic-sensitivity spectral positions for the FMG working line using multiple data sources and theoretical models.

Findings

Sensitivity peaks at line center for linear polarization.

Sensitivity is about -0.07 A from line center for circular polarization.

A spectral position of -0.08 A balances sensitivity for all Stokes parameters.

Abstract

Utilizing data from the $Solar$ $Magnetism$ and $Activity$ $Telescope$ (SMAT), analytical solutions of polarized radiative transfer equations, and in-orbit test data from the Full-disk Magnetograph (FMG) onboard the Advanced Space based Solar Observatory (ASO-S), this study reveals the magnetic-sensitivity spectral positions for the Fe {\sc i} $\lambda$5234.19 A, working line used by FMG. From the experimental data of SMAT, it is found that the most sensitivity position is located at the line center for linear polarization (Stokes-Q/U), while it is about -0.07 A away from the line center for circular polarization (Stokes-V). Moreover, both the theoretical analysis and the in-orbit test data analysis of FMG prove again the above results. Additionally, the theoretical analysis suggests the presence of distinct spectral pockets (centered at 0.08-0.15 A) from the line, harboring intense magnetic sensitivity across all three Stokes parameters. Striking a balance between high sensitivity for both linear and circular polarization while capturing additional valuable information, a spectral position of -0.08 A emerges as the champion for routine FMG magnetic-field observations.