Speaker
Description
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 balloon telescope. These lines reveal thread-like structures resembling spicules and exhibit systematically smaller Doppler velocities than Ca II 854.2 nm, indicating that they are optically thinner and more affected by line-of-sight averaging. Radiative transfer simulations using the spherical code rhsphere reproduce the overall spectral properties and support a recombination-driven formation mechanism. The observed ratios show significant dispersion and systematic deviations from one-dimensional model predictions. These results suggest that multi-dimensional and inhomogeneous plasma conditions play an important role in the formation of high-order Paschen lines, and demonstrate their potential as a new diagnostic of optically thin, recombination-dominated plasma in the off-limb chromosphere.