The Na i and Sr ii Resonance Lines in Solar Prominences

• Published in: Solar physics 2017-07, Vol.292 (7), Article 83
• Main Authors: Stellmacher, G., Wiehr, E.
• Format: Article
• Language: English
• Subjects: Astrophysics and Astroparticles; Atmospheric Sciences; Physics; Physics and Astronomy; Sciences of the Universe; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics
• ISSN: 0038-0938; 1573-093X
• DOI: 10.1007/s11207-017-1103-6

We estimate the electron density, n e , and its spatial variation in quiescent prominences from the observed emission ratio of the resonance lines Na  i  5890 Å (D 2 ) and Sr  ii  4078 Å. For a bright prominence ( τ α ≈ 25 ) we obtain a mean n e ≈ 2 × 10 10 cm − 3 ; for a faint one ( τ α ≈ 4 ) n e ≈ 4 × 10 10 cm − 3 on two consecutive days with moderate internal fluctuation and no systematic variation with height above the solar limb. The thermal and non-thermal contributions to the line broadening, T kin and V nth , required to deduce n e from the emission ratio Na  i /Sr  ii cannot be unambiguously determined from observed widths of lines from atoms of different mass. The reduced widths, Δ λ D / λ 0 , of Sr  ii  4078 Å show an excess over those from Na D 2 and H δ 4101  Å, assuming the same T kin and V nth . We attribute this excess broadening to higher non-thermal broadening induced by interaction of ions with the prominence magnetic field. This is suggested by the finding of higher macro-shifts of Sr  ii  4078 Å as compared to those from Na D 2 .