Stellar Wind Models

International audienceI present here some ideas on how jets from low mass stars may evolve as the star evolves from class 0 to the main sequence through classes I, II, III. Analytical models and simulations suggest that the ejection start very early in the life of a low mass star from the edge of the disk. Then, the jet is progressively ejected from a more central part of the system composed by the star and its accretion disk. Once the disk itself evaporates, the jet becomes a mere wind from the star which has reached the main sequence. This wind should be similar to the well known solar wind. To illustrate this point, we show specific applications of meridionally self-similar models to jets from T Tauris with a low mass accretion rate, as well as for the solar wind. We also present numerical simulations of turbulent stellar jets surrounded by a magnetized disk wind, which clearly show that the stellar jet may be an essential ingredient in preventing too fast and too tight collimation of the disk jet. At this point, note that I shall call in the rest of the present review ``stellar jet'', the component of the wind originating from the star and its vicinity, by opposition to the ``disk wind'' or ``disk jet'' that corresponds to the component emerging from the disk and more specifically from the Keplerian disk. The analytical solution can be further extended to the relativistic domain. The same dichotomy seems to exist for extragalactic jets. While sub relativitic winds from Seyferts may correspond to radial winds, radio loud jets are comparable to YSO jets. Nevertheless the distinction between FRI and FRII jets may be more a problem of environment and efficiency of the magnetic rotator as FRI jets evolve in a rich external medium, while the opposite holds for FRII