CORONAL ENVIRONMENT OF QUIESCENT PROMINENCES

With the spectro-coronagraph and the multichannel subtractive double pass spectrograph (MSDP) at the Pic du Midi Observatory two quiescent prominences were observed simultaneously. From the spectro-coronagraph observations 2D maps of He I lambda 10830 angstrom, Fe XIII angstrom 10798 and 10747 angstrom line intensities were obtained. In addition, we obtained 2D maps of the ratio R of the two iron lines. This ratio is used as a diagnostic for determining the density of the hot coronal plasma surrounding prominences. We found that the electron density is higher at the location of the prominences than in the corona, whereas small regions (approximately 40'') of lower electron density are unevenly distributed around the prominences indicating that the surrounding corona is highly inhomogeneous. The density of the cavity is reduced by a factor 1.5 compared to the density of the prominence environment (approximately 5 x 10(8) CM-3). We discuss the existence of cavities around these prominences according to the orientation of their axes relative to the line of sight and according to the velocity field inside the prominences. Constraints on models for prominence formation are derived.