Jets and Bipolar Outflows from Young Stars: Theory and Observational Tests

Jets and outflows from young stars are an integral part of the star formation process. A particular framework for explaining these phenomena is the X-wind theory. Since PPIV, we have made good progress in modeling the jet phenomena and their associated fundamental physical processes, in both deeply embedded Class I objects and more revealed classical T Tauri stars. In particular, we have improved the treatment of the atomic physics and chemistry for modeling jet emission, including reaction rates and interaction cross-sections, as well as ambipolar diffusion between ions and neutrals. We have broadened the original X-wind picture to include the winds driven magnetocentrifugally from the innermost disk regions. We have carried numerical simulations that follow the wind evolution from the launching surface to large, observable distances. The interaction between the magnetocentrifugal wind and a realistic ambient medium was also investigated. It allows us to generalize the shell model of Shu et al. (1991) to unify the the jet-driven and wind-driven scenarios for molecular outflow production. In addition, we review related theoretical works on jets and outflows from young stars, and make connection between theory and recent observations, particularly those from HST/STIS, VLA and SMA. 1