# The Na I and Sr II Resonance Lines in Solar Prominences

## TL;DR

This study estimates electron densities in solar prominences using Na I and Sr II resonance lines, revealing spatial variations and magnetic field interactions through line broadening and shifts.

## Contribution

It introduces a method to determine electron density and magnetic effects in prominences via resonance line emission ratios and line broadening analysis.

## Key findings

- Electron densities are around 2-4 x 10^10 /cm^3 in prominences.
- Higher non-thermal broadening affects ions more than neutral atoms.
- Sr II lines show greater broadening and shifts, indicating magnetic interactions.

## Abstract

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 (D2) and Sr II 4078. For a bright prominence (tau_alpha ~ 25) we obtain a mean n_e ~ 2*10^10 /cm^3; for a faint one (tau_alpha ~ 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 NaI/SrII cannot be unambiguously determined from observed widths of lines from atoms of different mass. The reduced widths, Delta-lambda_D / lambda_0, of Sr II 4078 show an excess over those from NaD2 and H-delta, 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 SrII4078 as compared to those from NaD2.