SIMBAD references

Although the presence of circumbinary disks around binary post-AGB stars is now well established, their actual structure, formation, stability and evolution remain largely unknown. We therefore used the MIDI interferometer to observe the disks around a sample of nine post-AGB binaries. These measurements show the very compact nature of the circumstellar environment and confirm the disk interpretation of their spectral energy distribution. In addition, a large diversity is observed in the radial distribution of the crystallinity over the N-band. While some objects show a homogeneous distribution of the crystallinity, for some objects the crystallinity is confined to the innermost regions. Whether this is a result of the formation process or due to annealing during the long storage time in the disk is not clear.