A model for collimated outflows in molecular clouds and the case of HH 7–11
Collimated outflows of high-velocity gas, with typical scale lengths of 0.01–0.2 pc, are often observed to be associated with linear chains of optical emission knots1, sometimes connected by faint nebulosities. The flows have been ascribed to the interaction between an energetic wind ejected by a young stellar object and circumstellar material. However, none of the acceleration and collimation mechanisms proposed so far can easily account for the most peculiar properties of the outflows, namely the almost constant spacing between the knots, their radial motion and the abrupt velocity changes along the flow, well illustrated by the prototype we use for our modelling, HH 7–11. We suggest here a new interpretation of the phenomenon, based on flows in a channel of variable cross-sectional area due to Kelvin–Helmholtz instabilities between the flow and the ambient medium; and present solutions of the Mach number equation for such a channel, which possess multiple critical points and shocks identified with the observed optical knots.
New insights into a familiar friend: COJ=2–1 mapping of the bipolar outflow source NGC 1333 (HH 7–11)
We have observed the bipolar outflow source NGC 1333 (HH 7–11) in theJ=2–1 transition of12CO, and find evidence for a strong westerly termination of the red outflow lobe at a velocityVlsr∼27 km s−1, together with maximal mean red-flow velocities Δv centred upon both the driving source SVS 13 and the westerly limit of the outflow zone. As a consequence, we propose a model for the source in which the red-shifted outflow is directly impinging upon a nearby molecular cloud, causing extensive surface erosion and/or diversion of the jet material.
A Two-Component Model of the Quiet Solar Wind with Viscosity, Magnetic Field, and Reduced Heat Conduction
Quiet solar wind two component model, including viscosity, magnetic field and reduced heat conduction