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.

arXiv comment9 pages, 12 figures, Accepted for publication in A&A

References in corpus (10)

• 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
• Non-LTE oxygen line formation in 3D hydrodynamic model stellar atmospheres
• Physical Properties of a Sunspot Chromosphere with Umbral Flashes
• Neutral oxygen spectral line formation revisited with new collisional data: large departures from LTE at low metallicity
• Excitation and charge transfer in low-energy hydrogen atom collisions with neutral atoms: Theory, comparisons, and application to Ca
• Electron-impact excitation of neutral oxygen
• The Formation of IRIS Diagnostics. VII. The Formation of the OI 135.56 nm Line in the Solar Atmosphere
• Off-disk straylight measurements for the Swedish 1-meter Solar Telescope

Cited by in corpus (4)

• Inelastic O+H collisions and the OI 777nm solar centre-to-limb variation
• 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