Statistical analysis of the Si I 6560.58 Å line observed by CHASE^⋆

¹ School of Astronomy and Space Science, Nanjing University, Nanjing 210023, PR China
e-mail: jiehong@nju.edu.cn
² Key Laboratory for Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210023, PR China
³ Yunnan Observatories, Chinese Academy of Sciences, Kunming 650216, PR China

Received: 6 July 2022
Accepted: 27 September 2022

Abstract

Context. The Si I 6560.58 Å line in the Hα blue wing is blended with a telluric absorption line from water vapor in ground-based observations. Recent observations with the space-based telescope, the Chinese Hα Solar Explorer (CHASE), provide a new opportunity to study this line.

Aims. We aim to study the Si I line statistically and to explore possible diagnostics.

Methods. We selected three scannings in the CHASE observations, and measured the equivalent width (EW) and the full width at half maximum (FWHM) for each pixel on the solar disk. We then calculated the theoretical EW and FWHM from the VALC model. We also studied an active region in particular in order to identify possible differences in the quiet Sun and the sunspots.

Results. The Si I line is formed at the bottom of the photosphere. The EW of this line increases from the disk center to μ = 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 μ = 0.2. We do not find any response to flare heating in the observations studied here. Doppler shifts and line widths of the Si I 6560.58 Å and Fe I 6569.21 Å lines can be used to study the mass flows and turbulence of the different photospheric layers. The Si I line shows significant potential as a tool to diagnose the dynamics and energy transport in the photosphere.