The arch systems, cavities and prominences in the helmet streamer observed at the solar eclipse, November 12, 1966

Abstract

Arch systems lying above quiescent prominences in the solar corona have long drawn the attention of eclipse observers, and such formations have been investigated since the end of the last century. Almost every eclipse photograph shows one or more arches, and in most cases the arch system is accompanied by a quiescent prominence below it and a helmet streamer above it. Also, in some cases there is a dark cavity between the arch systern and the prominence.On large-scale photographs obtained at the November 12, 1966 eclipse, detailed photometry has been carried out on a formation in the corona composed of a helmet streamer straddling two multiplearch systems each with a dark cavity and a quiescent prominence. The excess of electrons in the arches and the deficiency in the cavities are evaluated. We find that the formation of a prominence requires much more material than available in the cavity before depletion. Consequently the condensation theory of coronal matter into prominences seems to have difficulties explaining the necessary amount of matter in the cases where coronal arches -delineating magnetic field lines above the cavity -may exclude inflow of matcrial from the corona. We comment on the low velocity of solar wind in the helmet streamer.

Multi wavelength investigation of the eruption of a sigmoidal quiescent filament

“…A cavity is a natural way to do this. Cavities are known to exist in the vicinity of filaments in white light during eclipses or in Xray observations (Saito & Tandberg-Hanssen 1973;Vaiana et al 1973). The density in such structures is thought to be 2 to 4 times lower than in the surrounding corona, as indicated by Engvold (1988).…”

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

“…However, a significant question remains: how can the cool plasma inside the field lines be transported into the corona and kept there? It is recognized that this material should come from the chromosphere by either levitation or injection (Saito & Tandberg-Hanssen 1973). Sufficient mass must be extracted from the chromosphere by either magnetic forces that inject or lift the plasma or pressure forces that evaporate the plasma and then cool it to prominence temperatures.…”

Total Solar Eclipse Observations of Hot Prominence Shrouds

“…Their immediate surroundings are frequently characterized by reduced white light emission, which has led to the commonly used term of "prominence cavity." A system of concentric arch-like arcades is found to overlie the cavities (Saito & Tandberg-Hanssen 1973). When observed against the solar disk, prominences are called filaments, and both filaments and their associated cavities appear in absorption rather than emission.…”