Which jet launching mechanism(s) in T Tauri stars

Aims. We examine whether ejection phenomena from accreting T Tauri stars can be described by only one type of self-collimated jet model. Methods. We present analytical kinematic predictions valid soon after the Alfven surface for all types of steady magnetically s elf-confined jets. Results. We show that extended disc winds, X-winds, and stellar winds occupy distinct regions in the poloidal speed vs. specific an gular momentum plane. Comparisons with current observations of T Tauri jets yield quantitative constraints on the range of la unching radii, magnetic lever arms, and specific energy input in disc and stellar wind s. Implications on the origin of jet asymmetries and disc magnetic fields are outlined. Conclusions. We argue that ejection phenomena from accreting T Tauri stars most likely include three dynamical components: (1) an outer self-collimated steady disc wind carrying most of the mass-flux in the optical jet (when present), confining (2) a pressur e-driven coronal stellar wind and (3) a hot inner flow made of blobs sporadically ejecte d from the magnetopause. If the stellar magnetic moment is parallel to the disc magnetic field, then the highly variable inner flow resem bles a "Reconnection X-wind", that has been proven to effi ciently brake down an accreting and contracting young star. If the magnetic moment is anti-parallel, then larger versions of the solar coro nal mass ejections are likely to occur. The relative importance of these three components in the observed outflows and the range of radii involve d in the disc wind are expected to vary with time, from the stage of embedded source to the optically revealed T Tauri star phase.