Magnetized accretion-ejection structures. 1. General statements

The structure of accretion disks thread by opened magnetic field lines that drive jets by extracting angular momentum has been investigated. Accretion and ejection are thus complementary processes that cannot be separated, the magnetohydrodynamic (MHD) structure of accretion-ejection must be understood globally. Several classes of such structures have been selected for both active galactic nuclei (AGN) and young stellar objects (YSOs). A continuous transition from a standard hydrodynamic disk to a fully MHD accretion-ejection configuration can be achieved under three circumstances. The first one concerns the innermost radiative part of AGN accretion disks, whereas the other two concern YSOs disks, precisely, the grain and the molecular opacity dominated regions.