Jets and Tori in Proto–Planetary Nebulae

We investigate the time sequence for the appearance of jets and moleculartori in the transition of stars from the Asymptotic Giant Branch to theplanetary nebula phase. Jets and tori are prominent features of this evolution,but their origins are uncertain. Using optical and millimeter line kinematics,we determine the ejection history in a sample of well-observed cases. We findthat jets and tori develop nearly simultaneously. We also find evidence thatjets typically appear slightly later than tori, with a lag time of a fewhundred years. These characteristics provide strong evidence that jets and toriare physically related, and they set new constraints on theories of jetformation. The ejection of a discrete torus followed by jets on a short timescale favors the class of models in which a companion interacts with thecentral star. Models with long time scales, or with jets followed by a torus,are ruled out.Comment: 24 pages, 2 figures, to be published in Ap