Solar off-limb emission of the OI 7772 Å line

Abstract

The aim of this paper is to understand the formation of the OI line at 7772 Å in the solar chromosphere. We used SST/CRISP observations to observe OI 7772 Å in several places around the solar limb. We compared the observations with synthetic spectra calculated with the RH code in the one-dimension spherical geometry mode. New accurate hydrogen collisional rates were included for the RH calculations. The observations reveal a dark gap in the lower chromosphere, which is caused by variations in the line opacity as shown by our models. The lower level of the 7772 Å transition is populated by a downward cascade from the continuum. We study the effect of Lyman-$\beta$ pumping and hydrogen collisions between the triplet and quintet system in OI. Both have a small but non-negligible influence on the line intensity.

9 pages, 12 figures, Accepted for publication in A&A

References in corpus (4)

• CRISP Spectropolarimetric Imaging of Penumbral Fine Structure
• CRISPRED: A data pipeline for the CRISP imaging spectropolarimeter
• An Interface Region Imaging Spectrograph first view on Solar Spicules
• Electron-impact excitation of neutral oxygen

Cited by in corpus (3)

• Center-to-limb variation of spectral lines and continua observed with SST/CRISP and SST/CHROMIS
• Dark off-limb gap: manifestation of temperature minimum and dynamic nature of the chromosphere
• Detection of Doppler velocity differences between ions and neutrals in an erupting prominence