Helium Emissions Observed in Ground-Based Spectra of Solar Prominences
arXiv:1208.2153 · doi:10.1007/s11207-012-0118-2
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.
12 pages, 5 figure, 3 tables
References in corpus (4)
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- Spectroscopy of Solar Prominences Simultaneously from Space and Ground
- Radiative transfer in cylindrical threads with incident radiation VI. A hydrogen plus helium system
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- The Na I and Sr II Resonance Lines in Solar Prominences
- Non-thermal line-broadening in solar prominence
- Future Prospects for Partially Ionised Solar Plasmas: the Prominence Case
- Ionization memory of plasma emiters in a solar prominence