Jets and Brets in Planetary Nebulae

Abstract

The presence of high-velocity, collimated outflows in planetary nebulae (PNe) has been observationaly established in recent years. Furthermore, these collimated outflows, or jets, are usually found to be symmetric with respect to the nucleus. In some cases, their morphology and spatial distribution indicates episodic outbursts and rotation of the symmetry axis. In these cases, the bipolar, rotating, episodic jets are identified as BRETs. The existence of bipolar jets in PNe has been considered perplexing since the mechanisms for their formation are unclear. However, substantial progress in their study has been made in the last few years, from both theoretical and observational grounds. Consequently, new results in the field are rapidly coming out, as it can be noticed from the number of related works in this symposium. We still need to reach solid answers in many aspects of this field, but its influence in the study of PNe has already modified the traditional views of PNe shaping and evolution. The main characteristics of some of these phenomena are discussed here, together with prototypical cases, including a compilation of PNe with BRETs charateristics.