Broad-band Halpha HI coronagraphic observations

Broad-band full-limb H-alpha images of the inner corona are obtained since the beginning of the solar cycle 23 using one of the Pic-du-Midi coronagraph. A tool to process the complete set of stored images and to automatically extract the properties and the evolutions of the observed cold HI structures over a large range of sizes and light fluxes, from small jets and/or spikes to large prominences, was developed. We briefly remind the recognition techniques implemented in our software and discuss its use, including the best possible removal of the parasitic diffraction ring produced by the set of different occulting disks used along the Year. Following a statistical analysis of the occurrence of structure parameters applied to a large sample of observations, some new results are presented. It illustrates the capabilities of this software when applied to our database. Strong activity-asymmetries over the solar poles are shown. We also discuss the distribution of relative to the solar disk intensities light fluxes of these structures over a wide range of sizes and surfaces. In addition, full disk H-alpha images are obtained since 2005, on the same mount, to calibrate the height of the extended chromosphere and of off-limb structures, which seems to be an important parameter for predicting the occurrence of CMEs.

See also: http://bass2000.bagn.obs-mip.fr