The prominence-corona Interface

Abstract

The existence of cool and dense material in the hot and diluted corona implies specific mass and energy transfers between the two media. This is true for all steps in prominence lifetime : formation, quiescence and disappearance. Much theoretical work has been done recently on the formation by coronal condensation, but observational signatures are scarce, probably because of the long duration involved. On the contrary, the “Disparition Brusque” phenomenon has been observed in different wavelengths (temperatures) and shown to be either essentially magnetic or thermal. Line ratios have been used for the density diagnostics of eruptive prominences and point to a small filling factor. As for the quiet PCTR, the increase of Differential Emission Measure at lower temperatures, extensively studied with Skylab, is still a puzzle. With the help of both u-v (HRTS) and radio (VLA) new data, temperature gradients have been derived. The DEM increase could be explained by such heating process as waves or transients and also (at low temperature) by the reduction of radiative losses in optically thick lines. UVSP,observations on SMM indicate upflows and downflows in the PCTR. Their positions with respect to the magnetic field lines are unknown simply because no magnetic measurement exists in the PCTR. There is much activity in modeling prominences as a superposition of fine structures (threads, loops,..) in thermal equilibrium and in comparing with the uv emission. Obviously, we now have some information on pressure and temperature gradient in the PCTR but we do not know the geometry, the magnetic field nor the heating process. Further decisive progress will be made with the spectrometers and coronagraphs on SOHO.