MECHANISMS FOR THE PRODUCTION OF BIPOLAR FLOWS AND JETS IN STAR FORMATION REGIONS

Two types of mass ejection are associated with the formation of young stars: poorly collimated bipolar flows and well collimated jets. Some mechanisms which have been suggested for the driving of these flows are reviewed. These include centrifugally driven magnetised winds, magnetic pressure driven winds and bubbles driven by ionised or neutral winds. The idea that the bipolar flows are bubbles driven by a neutral wind seems attractive on both theoretical and observational grounds, but the source of the neutral wind-disk or star-is uncertain. It is possible that the jets are driven by magnetic pressure or by a rapidly rotating magnetic field close to the star. However, no definitive theory exists at the present time.