Shaping the envelope of the asymptotic giant branch star W43A with a collimated fast jet.
TAFOYA D., IMAI H., GOMEZ J.F., NAKASHIMA J.-I., OROSZ G. and YUNG B.H.K.
Abstract (from CDS):
One of the major puzzles in the study of stellar evolution is the formation process of bipolar and multipolar planetary nebulae. There is growing consensus that collimated jets create cavities with dense walls in the slowly expanding (10-20 km s–1) envelope ejected in previous evolutionary phases, leading to the observed morphologies. However, the launching of the jet and the way it interacts with the circumstellar material to create such asymmetric morphologies have remained poorly known. Here we present for the first time CO emission from the asymptotic giant branch star W43A that traces the whole stream of a jet, from the vicinity of its driving stellar system out to the regions where it shapes the circumstellar envelope. We found that the jet has a launch velocity of 175 km s–1 and decelerates to a velocity of 130 km s–1 as it interacts with circumstellar material. The continuum emission reveals a bipolar shell with a compact bright dot in the center that pinpoints the location of the driving source of the jet. The kinematical ages of the jet and the bipolar shell are equal, τ ∼ 60 yr, indicating that they were created simultaneously, probably by a common underlying mechanism, and in an extremely short time. These results provide key initial conditions for the theoretical models that aim to explain the formation of bipolar morphologies in the circumstellar envelopes of low- and intermediate-mass stars.