The shaping effect of collimated fast outflows in the egg nebula

Abstract

We present high angular resolution observations of the HC 3N J = 5-4 line from the Egg nebula, which is the archetype of proto-planetary nebulae (PPNs). We find that the HC 3N emission in the approaching and receding portion of the envelope traces a clumpy hollow shell, similar to that seen in normal carbon-rich envelopes. Near the systemic velocity, the hollow shell is fragmented into several large blobs or arcs with missing portions correspond spatially to locations of previously reported high-velocity outflows in the Egg nebula. This provides direct evidence for the disruption of the slowly expanding envelope ejected during the AGB phase by the collimated fast outflows initiated during the transition to the PPN phase. From modeling the HC 3N distribution, we could reproduce qualitatively the spatial kinematics of the HC 3N J = 5-4 emission using a HC 3N shell with two pairs of cavities cleared by the collimated high-velocity outflows along the polar direction and in the equatorial plane. We infer a relatively high abundance of HC 3N/H 2 3 × 10 -6 for an estimated mass-loss rate of 3 × 10 -5 M⊙ yr -1 in the HC 3N shell. The high abundance of HC 3N and the presence of some weaker J = 5-4 emission in the vicinity of the central post-AGB star suggest an unusually efficient formation of this molecule in the Egg nebula. © 2009. The American Astronomical Society.