High-order Paschen emission from the quiet-Sun off-limb chromosphere

Haocheng Yu; Yukio Katsukawa; Mingde Ding; Takuma Matsumoto; Sami K. Solanki; Julian Blanco Rodríguez; David Orozco Suárez; Masahito Kubo; Andreas Lagg; Achim Gandorfer; José Carlos del Toro Iniesta; Pietro Bernasconi; Thomas Berkefeld; Alex Feller; Tino L. Riethmüller; Alberto Álvarez-Herrero; H. N. Smitha; Bianca Grauf; Michael Carpenter; Alexander Bell; Valentín Martínez Pillet; Francisco Javier Bailén; Juan Sebastián Castellanos Durán; Edvarda Harnes; Johannes Hölken; Francisco A. Iglesias; Ryohtaroh T. Ishikawa; Yusuke Kawabata; Takayoshi Oba; Azaymi L. Siu-Tapia; Hanna Strecker; Dušan Vukadinović; Hirohisa Hara; Toshifumi Shimizu

arXiv · 2608.14034

High-order Paschen emission from the quiet-Sun off-limb chromosphere

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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 {\sc Sunrise~iii} balloon telescope. These lines reveal thread-like 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 \texttt{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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Haocheng Yu, Yukio Katsukawa, Mingde Ding, Takuma Matsumoto, Sami K. Solanki, Julian Blanco Rodríguez, David Orozco Suárez, Masahito Kubo, Andreas Lagg, Achim Gandorfer, José Carlos del Toro Iniesta, Pietro Bernasconi, Thomas Berkefeld, Alex Feller, Tino L. Riethmüller, Alberto Álvarez-Herrero, H. N. Smitha, Bianca Grauf, Michael Carpenter, Alexander Bell, Valentín Martínez Pillet, Francisco Javier Bailén, Juan Sebastián Castellanos Durán, Edvarda Harnes, Johannes Hölken, Francisco A. Iglesias, Ryohtaroh T. Ishikawa, Yusuke Kawabata, Takayoshi Oba, Azaymi L. Siu-Tapia, Hanna Strecker, Dušan Vukadinović, Hirohisa Hara, Toshifumi Shimizu. 2026-08-14. High-order Paschen emission from the quiet-Sun off-limb chromosphere. https://arxiv.org/abs/2608.14034

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