Co outflows from young stars: Confronting the jet and wind models

We have mapped the CO J = 1-0 emission from molecular outflows associated with five young stellar systems of class O to class II/III using the BIMA array and the FCRAO 14 m antenna. The systems, VLA 05487, HH 212, HH 240/241, HH 111, and RNO 91, are all relatively nearby and of low luminosity, and the majority have H₂ emission or optical jet features. The CO outflow generally forms a shell structure around the outflow axis with the higher velocity emission further out from the source. Two distinctive kinematic features are evident in position-velocity (PV) diagrams : a parabolic structure originating at the driving source (e.g., VLA 05487 and HH 111) and a convex spur structure with the high-velocity tip near known H₂ bow shocks (e.g., HH 212, HH 240/241 and HH 111). The parabolic PV structure can be produced by a wide-angle-wind model, while the velocity spur structure can be modeled with a jet-driven bow shock model. VLA 05487, which is not associated with any H₂ bow shocks, shows only the parabolic structure and kinematics consistent with the wide-angle wind-driven model. HH 212, which is associated with a series of H₂ bow shock structures, shows a striking morphological coincidence between the H₂ and CO emission and velocity spurs in the PV diagram. It is our best example of the jet-driven bow shock model, and its kinematics can be qualitatively explained in that context. HH 240/241 is similar to HH 212 and shows a close relationship between the H₂ and CO emission. The kinematics of its western lobe can also be explained with the jet-driven model. The kinematics of RNO 91 are similar to VLA 05487 and are broadly consistent with a wide-angle wind-driven model. HH 111 has both parabolic and spur PV structures, a combination that is not easily explained in the simplest version of either model. Thus, these observations provide examples of systems that support either the wide-angle wind-driven or jet-driven model in the simplest interpretation. More detailed calculations are needed to understand whether one model might be able to fit all systems. It is crucial to know if time-dependent or long-lived jet-driven bow shock models can produce the observed outflow widths and parabolic PV structures, or if a wide-angle wind can produce the shock features and velocity spur structures in our observations.