Velocity Difference of Ions and Neutrals in Solar Prominences

Abstract

Abstract Marked velocity excesses of ions relative to neutrals are obtained from two time series of the neighboring emission lines He i 5015 Å and Fe ii 5018 Å 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 ≤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 minutes. The ratio excess is superposed by a time- and velocity-independent “difference excess” of −0.3 ≤ V macro(Fe ii)−V macro(He i) ≤ +0.7 km s−1 in series A (also indicated in series B). The high repetition rate of 3.9 s enables the detection of high-frequency oscillations with several damped 22 s 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.