Helium Emissions Observed in Ground-Based Spectra of Solar Prominences
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.
Keywords
Cite
@article{arxiv.1208.2153,
title = {Helium Emissions Observed in Ground-Based Spectra of Solar Prominences},
author = {Renzo Ramelli and Goetz Stellmacher and Eberhard Wiehr and Michele Bianda},
journal= {arXiv preprint arXiv:1208.2153},
year = {2016}
}
Comments
12 pages, 5 figure, 3 tables