Velocity vectors of a quiescent prominence observed by Hinode/SOT and the MSDP (Meudon)

Context. The dynamics of prominence fine structures present a challenge to our understanding of the formation of cool plasma prominence embedded in the hot corona. Aims. Observations performed by the high resolution Hinode/SOT telescope allow us to compute velocities perpendicular to the lineof-sight or transverse velocities. Combining simultaneous observations obtained in Hα with Hinode/SOT and the MSDP spectrograph operating in the Meudon solar tower, we derive the velocity vectors of a quiescent prominence. Methods. The velocities perpendicular to the line-of-sight are measured using a time-slice technique and the Doppler shifts velocity using the bisector method. Results. The Doppler shifts of bright threads derived from the MSDP show counterstreaming of the order of 5 kms −1 in the prominence and reaching 15 kms −1 at the edges of the prominence. Even though they are minimum values because of seeing effects, they are of the same order as the transverse velocities. Conclusions. These measurements are very important because they suggest that the vertical structures detected by SOT may not be true vertical magnetic structures in the sky plane. The vertical structures could be a pile up of dips in more or less horizontal magnetic field lines in a 3D perspective, as proposed by many MHD modelers. In our analysis, we also calibrate the Hinode Hα data using MSDP observations obtained simultaneously.