Radio Metric Observations of Quiescent Filament Cavities

We present in this paper a systematic study of the filament environment in the metric radio range, describing the existence of brightness temperature depressions above quiescent filaments on the disk and on the limb. Using the upgraded Nancay Radioheliograph, Hα data from Meudon Observatory, and EIT and LASCO data from SOHO, we estimate the brightness temperature depressions and show that the most likely source of the depression is the cavity that surrounds the filament. Radio observations are able to locate and probe this cavity on the disk, contrary to other wavelengths. Using a filament eruption as an example, we propose that the cavity is a magnetic structure linked to the filament, in accordance with flux-rope models.