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\section{Introduction}   In many areas of astrophysics compact central objects accrete mass and angular momentum from a disk and at the same time they eject a highly collimated jet. This is seen for central objects as massive as AGN or as light as (proto) brown dwarfs. For objects like AGN or accreting neutron stars the jets reach relativistic energies while the velocities are significantly lower in young stellar systems. objects (YSOs).  A large number of jets is observed in near star forming regions, where the jet composition and structure can be studied in great detail \citep[see the review by][]{2014arXiv1402.3553F}.  Jets are launched from the early stages of star formation until the accretion from the circumstellar disk ceeds. Jets from very young stars (class I) are the most powerful and can be traced for long distances up to a parsec from the source, but the central engine is still deeply embedded in a dense envelope of gas and dust and thus cannot be observed directly. As the young stellar objects evolve, mass from the envelope becomes thinner and accretes onto the circumstellar disk. In this stage young, low-mass stars that actively accrete from their circum-stellar disk are called classical T Tauri stars \citep[for a review see][]{2013AN....334...67G}. Their jets often only reach a few hundred AU (and are thus sometimes called ``mircojets'' in comparison to the outflows from younger objects), but the lower column density makes the jet acessibly to observations just a few tens of AU from the central star.