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arXiv · 1208.2153

Helium Emissions Observed in Ground-Based Spectra of Solar Prominences

Renzo Ramelli·Goetz Stellmacher·Eberhard Wiehr·Michele Bianda
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Abstract

The only prominent line of singly ionized helium in the visible spectral range, helium-II 4686 A, is observed together with the helium-I 5015 A singlet and the helium-I 4471 A triplet line in solar prominences. The sodium emission, NaD2, is used as a tracer for helium-II emissions which are sufficiently bright to exceed the noise level near 10^-6 of the disk-center intensity. The so selected prominences are characterized by small non-thermal line broadening and almost absent velocity shifts, yielding narrow line profiles without wiggles. The reduced widths [Delta(lambda_D) / lambda] of helium-II 4686 A are 1.5 times broader than those of helium-I 4471 A triplet and 1.65 times broader than those of helium-I 5015 A singlet. This indicates that the helium lines originate in a prominence--corona transition region with outwards increasing temperature.

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Renzo Ramelli, Goetz Stellmacher, Eberhard Wiehr, Michele Bianda. 2012-10-02. Helium Emissions Observed in Ground-Based Spectra of Solar Prominences. https://doi.org/10.1007/s11207-012-0118-2

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