Line-of-sight velocity fluctuations of a quiescent prominence

Series of H alpha spectra and slit-jaw H alpha filtergrams of a quiescent p rominence taken at Pic du Midi Observatory on 7 November 1977 are studied. The observations have been digitized by means of an automated Joyce Loebl m icrodensitometer. The image processing of the H alpha filtergrams reveals a n internal structure of the prominence consisting of several arches. Series of high-resolution H alpha spectra obtained with the slit position located on a selected part of one of the prominence arches have been chosen for Do ppler-shift analysis. The obtained time series of the line-of-sight velocit y reveal large velocity variations near the periphery of the arch and a str ong dependence of the velocity (in sign and magnitude) on the position alon g the slit. The prominence arch shows also cyclic displacements along the l ine-of-sight direction implying Alfven string-mode oscillations.