# Evidence for the two fluid scenario in solar prominences

## TL;DR

This study provides observational evidence supporting the two-fluid model in solar prominences, showing different behaviors of neutral and ionized species, with implications for prominence dynamics and plasma interactions.

## Contribution

It offers new observational data demonstrating the differential motion of ions and neutrals in prominences, supporting the two-fluid scenario with detailed spectral analysis.

## Key findings

- Ionic species exhibit larger Doppler shifts than neutral species.
- The velocity excess between ions and neutrals varies with prominence activity.
- Electron density remains relatively constant despite velocity changes.

## Abstract

This paper presents observational evidence of the different dynamical behavior of neutral and ionized species in solar prominences. The analysis of a time-series of Sr II 4078 A and Na D spectra in a quiescent prominence yields systematically larger Doppler shifts (line-of-sight velocities) for the ions V_LOS(Sr II)= 1.22 x V_LOS (Na D). Both lines show a 30 min oscillation of good coherence. Sixteen hours later the same prominence underwent marked morphological changes (with a rising dome), and the Sr II velocity excess drops to V_LOS(Sr II)=1.11 x V_LOS(Na D). The same excess is found for the line pair Fe II 5018 A and He I 5015 A. The widths of the ionic lines, mainly non-thermally broadened, are not related to the macro velocities. The emission ratio of Na D and Sr II, a measure of the electron density, yields n_e = 4 x 10^10 1/cm, shows no relation with the V_LOS variation or with height above the limb, and seems to be reduced 16 hr later during the active phase. We apply a new wavelength reference from aureola spectra, which is independent of photospheric velocity fields.