Evolution from Spherical AGB Wind to Multipolar Outflow in Pre-planetary Nebula IRAS 17150−3224

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Abstract We have mapped the pre-planetary nebula IRAS 17150−3224 in the 350 GHz continuum and CO J = 3–2 line at an angular resolution of ∼0.″09 using the Atacama Large Millimeter/submillimeter Array. A continuum source is detected at the center of the nebula, elongated along the equatorial plane, likely tracing a dusty torus around the central source. Continuum emission is also detected on both sides of the central continuum source in the equatorial plane, probably resulting from interactions of collimated fast winds (CFWs) with envelope material in the equator. CO emission is detected along the optical lobe. Although the optical lobe appears as bipolar, the CO map shows that it is actually a quadrupolar outflow consisting of two overlapping bipolar outflows. Two additional younger bipolar outflows are also detected in CO, one at the lower latitude and the other along the equatorial plane. In the CO position–velocity maps, blueshifted absorption stripes are detected in the outflow emissions, due to absorption by a series of shells produced by a series of asymptotic giant branch (AGB) wind ejections. By modeling the morphology and kinematics of the AGB wind and outflows, we find that the AGB wind could have ended ∼1300 yr ago, the quadrupolar outflow was ejected ∼350 yr ago, and the two additional bipolar outflows were ejected ∼280 and 200 yr ago, respectively. The outflows could be produced either by bullets coming from an explosion, or by a precessing CFW with a time-dependent ejection velocity.