Statistical analysis of the Si I 6560.58 \r{A} line observed by CHASE

TL;DR

This study statistically analyzes the Si I 6560.58 Å line observed by CHASE, comparing observations with models to explore its diagnostic potential for photospheric dynamics and turbulence.

Contribution

It provides the first statistical analysis of the Si I 6560.58 Å line using space-based observations and compares observed and theoretical line parameters to assess diagnostic capabilities.

Findings

EW increases from disk center to μ=0.2 then decreases towards limb

FWHM increases monotonically from disk center to limb

Theoretical EW matches observations, but FWHM is underestimated in models

Abstract

The Si I 6560.58 \r{A} line in the H$\alpha$ blue wing is blended with a telluric absorption line from water vapor in ground-based observations. Recent observations with the space-based telescope CHASE provide a new window to study this line. We aim to study the Si I line statistically and to explore possible diagnostics. We select three scannings in the CHASE observations, and measure the equivalent width (EW) and the full width at half maximum (FWHM) for each pixel on the solar disk. We then calculate the theoretical EW and FWHM from the VALC model. An active region is also studied in particular for difference in the quiet Sun and the sunspots. The Si I line is formed at the bottom of the photosphere. The EW of this line increases from the disk center to $\mu$ = 0.2, and then decreases toward the solar limb, while the FWHM shows a monotonically increasing trend. Theoretically predicted EW agrees well with observations, while the predicted FWHM is far smaller due to the absence of unresolved turbulence in models. The macroturbulent velocity is estimated to be 2.80 km s$^{-1}$ at the disk center, and increases to 3.52 km s$^{-1}$ at $\mu$ = 0.2. We do not find any response to flare heating in current observations. Doppler shifts and line widths of the Si I 6560.58 \r{A} and Fe I 6569.21 \r{A} lines can be used to study the mass flows and turbulence of the different photospheric layers. The Si I line has good potentials to diagnose the dynamics and energy transport in the photosphere.