Classical T Tauri stars are low mass young forming stars that are surroundedby a circumstellar accretion disc from which they gain mass. Despite thisaccretion and their own contraction that should both lead to their spin up,these stars seem to conserve instead an almost constant rotational period aslong as the disc is maintained. Several scenarios have been proposed in theliterature in order to explain this puzzling "disc-locking" situation: eitherdeposition in the disc of the stellar angular momentum by the stellarmagnetosphere or its ejection through winds, providing thereby an explanationof jets from Young Stellar Objects. In this lecture, these various mechanisms will be critically detailed, fromthe physics of the star-disc interaction to the launching of self-confined jets(disc winds, stellar winds, X-winds, conical winds). It will be shown that nosimple model can account alone for the whole bulk of observational data andthat "disc locking" requires a combination of some of them.
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