High-order Paschen Emission from the Quiet-Sun Off-limb Chromosphere

Résumé fourni par la source

Abstract We report the detection of high-order hydrogen Paschen emission lines (Pa 15, Pa 16, and Pa 17) in the quiet-Sun chromosphere off the solar limb using the Chromospheric Infrared SpectroPolarimeter (SCIP) on board the Sunrise iii balloon telescope. These lines reveal threadlike structures resembling spicules and exhibit systematically smaller Doppler velocities than Ca II 854.2 nm, suggesting that they are optically thinner and more affected by line-of-sight averaging, especially near the limb. Non-LTE radiative transfer synthesis using the spherically symmetric one-dimensional code rhsphere reproduces the overall spectral properties. The observed ratios among three Paschen lines show systematic deviations from synthetic and theoretical results, suggesting that additional physical effects may influence the formation of high-order Paschen lines. The study demonstrates the potential of high-order Paschen lines as a new diagnostic of optically thin plasma in the off-limb chromosphere.

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