Velocity difference of ions and neutrals in solar prominences

TL;DR

This study observes ion-neutral velocity differences in solar prominences, revealing quasi-periodic variations, a consistent ion velocity excess, and high-frequency oscillations, contributing to understanding plasma dynamics in solar prominences.

Contribution

It provides detailed measurements of ion-neutral velocity differences in prominences, showing temporal and spatial restrictions and high-frequency oscillations, advancing previous findings.

Findings

Ion velocities show quasi-periodic variations with ions faster than neutrals.

A consistent ion velocity excess ratio of 1.22 was confirmed.

High-frequency oscillations with damped 22 sec periods were detected.

Abstract

Marked velocity excesses of ions relative to neutrals are obtained from two time series of the neighboring emission lines He I 5015 and Fe II 5018 in a quiescent prominence. Their Doppler shifts show time variations of quasi-periodic character where the ions are faster than the neutrals 1.0 < V_macro(Fe II)/V_macro(He I) < 1.35 in series-A and, respectively, <1.25 in series-B. This 'ratio excess' confirms our earlier findings of a 1.22 ion velocity excess, but the present study shows a restriction in space and time of typically 5 Mm and 5 min. The ratio excess is superposed by a time and velocity independent 'difference excess' -0.3 < V_macro(Fe II)-V_macro(He I) < +0.7 km/s in series-A (also indicated in series-B). The high repetition rate of 3.9 sec enables the detection of high frequency oscillations with several damped 22 sec periods in series-A. These show a ratio excess with a maximum of 1.7. We confirm the absence of a significant phase delay of He neutrals with respect to the Fe ions.